text: /*
   * Matroska muxer
   * Copyright (c) 2007 David Conrad
   *
   * This file is part of FFmpeg.
   *
   * FFmpeg is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or (at your option) any later version.
   *
   * FFmpeg is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with FFmpeg; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
   */
  
  #include <stdint.h>
  
  #include "avc.h"
  #include "hevc.h"
  #include "avformat.h"
  #include "avio_internal.h"
  #include "avlanguage.h"
  #include "flacenc.h"
  #include "internal.h"
  #include "isom.h"
  #include "matroska.h"
  #include "riff.h"
  #include "subtitles.h"
  #include "vorbiscomment.h"
  #include "wv.h"
  
  #include "libavutil/avstring.h"
  #include "libavutil/channel_layout.h"
  #include "libavutil/crc.h"
  #include "libavutil/dict.h"
  #include "libavutil/intfloat.h"
  #include "libavutil/intreadwrite.h"
  #include "libavutil/lfg.h"
  #include "libavutil/mastering_display_metadata.h"
  #include "libavutil/mathematics.h"
  #include "libavutil/opt.h"
  #include "libavutil/parseutils.h"
  #include "libavutil/random_seed.h"
  #include "libavutil/rational.h"
  #include "libavutil/samplefmt.h"
  #include "libavutil/sha.h"
  #include "libavutil/stereo3d.h"
  
  #include "libavcodec/xiph.h"
  #include "libavcodec/mpeg4audio.h"
  #include "libavcodec/internal.h"
  
  typedef struct ebml_master {
      int64_t         pos;                ///< absolute offset in the file where the master's elements start
      int             sizebytes;          ///< how many bytes were reserved for the size
  } ebml_master;
  
  typedef struct mkv_seekhead_entry {
      unsigned int    elementid;
      uint64_t        segmentpos;
  } mkv_seekhead_entry;
  
  typedef struct mkv_seekhead {
      int64_t                 filepos;
      int64_t                 segment_offset;     ///< the file offset to the beginning of the segment
      int                     reserved_size;      ///< -1 if appending to file
      int                     max_entries;
      mkv_seekhead_entry      *entries;
      int                     num_entries;
  } mkv_seekhead;
  
  typedef struct mkv_cuepoint {
      uint64_t        pts;
      int             stream_idx;
      int             tracknum;
      int64_t         cluster_pos;        ///< file offset of the cluster containing the block
      int64_t         relative_pos;       ///< relative offset from the position of the cluster containing the block
      int64_t         duration;           ///< duration of the block according to time base
  } mkv_cuepoint;
  
  typedef struct mkv_cues {
      int64_t         segment_offset;
      mkv_cuepoint    *entries;
      int             num_entries;
  } mkv_cues;
  
  typedef struct mkv_track {
      int             write_dts;
      int             has_cue;
      int             sample_rate;
      int64_t         sample_rate_offset;
      int64_t         codecpriv_offset;
      int64_t         ts_offset;
  } mkv_track;
  
  typedef struct mkv_attachment {
      int             stream_idx;
      uint32_t        fileuid;
  } mkv_attachment;
  
  typedef struct mkv_attachments {
      mkv_attachment  *entries;
      int             num_entries;
  } mkv_attachments;
  
  #define MODE_MATROSKAv2 0x01
  #define MODE_WEBM       0x02
  
  /** Maximum number of tracks allowed in a Matroska file (with track numbers in
   * range 1 to 126 (inclusive) */
  #define MAX_TRACKS 126
  
  typedef struct MatroskaMuxContext {
      const AVClass  *class;
      int             mode;
      AVIOContext   *dyn_bc;
      AVIOContext     *tags_bc;
      ebml_master     tags;
      AVIOContext     *info_bc;
      ebml_master     info;
      AVIOContext     *tracks_bc;
      ebml_master     tracks_master;
      ebml_master     segment;
      int64_t         segment_offset;
      ebml_master     cluster;
      int64_t         cluster_pos;        ///< file offset of the current cluster
      int64_t         cluster_pts;
      int64_t         duration_offset;
      int64_t         duration;
      mkv_seekhead    *main_seekhead;
      mkv_cues        *cues;
      mkv_track       *tracks;
      mkv_attachments *attachments;
  
      AVPacket        cur_audio_pkt;
  
      int have_attachments;
      int have_video;
  
      int reserve_cues_space;
      int cluster_size_limit;
      int64_t cues_pos;
      int64_t cluster_time_limit;
      int is_dash;
      int dash_track_number;
      int is_live;
      int write_crc;
  
      uint32_t chapter_id_offset;
      int wrote_chapters;
  
      int64_t last_track_timestamp[MAX_TRACKS];
  
      int64_t* stream_durations;
      int64_t* stream_duration_offsets;
  
      int allow_raw_vfw;
  } MatroskaMuxContext;
  
  
  /** 2 bytes * 3 for EBML IDs, 3 1-byte EBML lengths, 8 bytes for 64 bit
   * offset, 4 bytes for target EBML ID */
  #define MAX_SEEKENTRY_SIZE 21
  
  /** per-cuepoint-track - 5 1-byte EBML IDs, 5 1-byte EBML sizes, 4
   * 8-byte uint max */
  #define MAX_CUETRACKPOS_SIZE 42
  
  /** per-cuepoint - 2 1-byte EBML IDs, 2 1-byte EBML sizes, 8-byte uint max */
  #define MAX_CUEPOINT_SIZE(num_tracks) 12 + MAX_CUETRACKPOS_SIZE * num_tracks
  
  /** Seek preroll value for opus */
  #define OPUS_SEEK_PREROLL 80000000
  
  static int ebml_id_size(unsigned int id)
  {
      return (av_log2(id + 1) - 1) / 7 + 1;
  }
  
  static void put_ebml_id(AVIOContext *pb, unsigned int id)
  {
      int i = ebml_id_size(id);
      while (i--)
          avio_w8(pb, (uint8_t)(id >> (i * 8)));
  }
  
  /**
   * Write an EBML size meaning "unknown size".
   *
   * @param bytes The number of bytes the size should occupy (maximum: 8).
   */
  static void put_ebml_size_unknown(AVIOContext *pb, int bytes)
  {
      av_assert0(bytes <= 8);
      avio_w8(pb, 0x1ff >> bytes);
      ffio_fill(pb, 0xff, bytes - 1);
  }
  
  /**
   * Calculate how many bytes are needed to represent a given number in EBML.
   */
  static int ebml_num_size(uint64_t num)
  {
      int bytes = 1;
      while ((num + 1) >> bytes * 7)
          bytes++;
      return bytes;
  }
  
  /**
   * Write a number in EBML variable length format.
   *
   * @param bytes The number of bytes that need to be used to write the number.
   *              If zero, any number of bytes can be used.
   */
  static void put_ebml_num(AVIOContext *pb, uint64_t num, int bytes)
  {
      int i, needed_bytes = ebml_num_size(num);
  
      // sizes larger than this are currently undefined in EBML
      av_assert0(num < (1ULL << 56) - 1);
  
      if (bytes == 0)
          // don't care how many bytes are used, so use the min
          bytes = needed_bytes;
      // the bytes needed to write the given size would exceed the bytes
      // that we need to use, so write unknown size. This shouldn't happen.
      av_assert0(bytes >= needed_bytes);
  
      num |= 1ULL << bytes * 7;
      for (i = bytes - 1; i >= 0; i--)
          avio_w8(pb, (uint8_t)(num >> i * 8));
  }
  
  static void put_ebml_uint(AVIOContext *pb, unsigned int elementid, uint64_t val)
  {
      int i, bytes = 1;
      uint64_t tmp = val;
      while (tmp >>= 8)
          bytes++;
  
      put_ebml_id(pb, elementid);
      put_ebml_num(pb, bytes, 0);
      for (i = bytes - 1; i >= 0; i--)
          avio_w8(pb, (uint8_t)(val >> i * 8));
  }
  
  static void put_ebml_sint(AVIOContext *pb, unsigned int elementid, int64_t val)
  {
      int i, bytes = 1;
      uint64_t tmp = 2*(val < 0 ? val^-1 : val);
  
      while (tmp>>=8) bytes++;
  
      put_ebml_id(pb, elementid);
      put_ebml_num(pb, bytes, 0);
      for (i = bytes - 1; i >= 0; i--)
          avio_w8(pb, (uint8_t)(val >> i * 8));
  }
  
  static void put_ebml_float(AVIOContext *pb, unsigned int elementid, double val)
  {
      put_ebml_id(pb, elementid);
      put_ebml_num(pb, 8, 0);
      avio_wb64(pb, av_double2int(val));
  }
  
  static void put_ebml_binary(AVIOContext *pb, unsigned int elementid,
                              const void *buf, int size)
  {
      put_ebml_id(pb, elementid);
      put_ebml_num(pb, size, 0);
      avio_write(pb, buf, size);
  }
  
  static void put_ebml_string(AVIOContext *pb, unsigned int elementid,
                              const char *str)
  {
      put_ebml_binary(pb, elementid, str, strlen(str));
  }
  
  /**
   * Write a void element of a given size. Useful for reserving space in
   * the file to be written to later.
   *
   * @param size The number of bytes to reserve, which must be at least 2.
   */
  static void put_ebml_void(AVIOContext *pb, uint64_t size)
  {
      int64_t currentpos = avio_tell(pb);
  
      av_assert0(size >= 2);
  
      put_ebml_id(pb, EBML_ID_VOID);
      // we need to subtract the length needed to store the size from the
      // size we need to reserve so 2 cases, we use 8 bytes to store the
      // size if possible, 1 byte otherwise
      if (size < 10)
          put_ebml_num(pb, size - 2, 0);
      else
          put_ebml_num(pb, size - 9, 8);
      ffio_fill(pb, 0, currentpos + size - avio_tell(pb));
  }
  
  static ebml_master start_ebml_master(AVIOContext *pb, unsigned int elementid,
                                       uint64_t expectedsize)
  {
      int bytes = expectedsize ? ebml_num_size(expectedsize) : 8;
      put_ebml_id(pb, elementid);
      put_ebml_size_unknown(pb, bytes);
      return (ebml_master) {avio_tell(pb), bytes };
  }
  
  static void end_ebml_master(AVIOContext *pb, ebml_master master)
  {
      int64_t pos = avio_tell(pb);
  
      if (avio_seek(pb, master.pos - master.sizebytes, SEEK_SET) < 0)
          return;
      put_ebml_num(pb, pos - master.pos, master.sizebytes);
      avio_seek(pb, pos, SEEK_SET);
  }
  
  static int start_ebml_master_crc32(AVIOContext *pb, AVIOContext **dyn_cp, MatroskaMuxContext *mkv,
                                     ebml_master *master, unsigned int elementid, uint64_t expectedsize)
  {
      int ret;
  
      if ((ret = avio_open_dyn_buf(dyn_cp)) < 0)
          return ret;
  
      if (pb->seekable & AVIO_SEEKABLE_NORMAL) {
          *master = start_ebml_master(pb, elementid, expectedsize);
          if (mkv->write_crc && mkv->mode != MODE_WEBM)
              put_ebml_void(*dyn_cp, 6); /* Reserve space for CRC32 so position/size calculations using avio_tell() take it into account */
      } else
          *master = start_ebml_master(*dyn_cp, elementid, expectedsize);
  
      return 0;
  }
  
  static void end_ebml_master_crc32(AVIOContext *pb, AVIOContext **dyn_cp, MatroskaMuxContext *mkv,
                                    ebml_master master)
  {
      uint8_t *buf, crc[4];
      int size, skip = 0;
  
      if (pb->seekable & AVIO_SEEKABLE_NORMAL) {
          size = avio_close_dyn_buf(*dyn_cp, &buf);
          if (mkv->write_crc && mkv->mode != MODE_WEBM) {
              skip = 6; /* Skip reserved 6-byte long void element from the dynamic buffer. */
              AV_WL32(crc, av_crc(av_crc_get_table(AV_CRC_32_IEEE_LE), UINT32_MAX, buf + skip, size - skip) ^ UINT32_MAX);
              put_ebml_binary(pb, EBML_ID_CRC32, crc, sizeof(crc));
          }
          avio_write(pb, buf + skip, size - skip);
          end_ebml_master(pb, master);
      } else {
          end_ebml_master(*dyn_cp, master);
          size = avio_close_dyn_buf(*dyn_cp, &buf);
          avio_write(pb, buf, size);
      }
      av_free(buf);
      *dyn_cp = NULL;
  }
  
  /**
  * Complete ebml master whithout destroying the buffer, allowing for later updates
  */
  static void end_ebml_master_crc32_preliminary(AVIOContext *pb, AVIOContext **dyn_cp, MatroskaMuxContext *mkv,
      ebml_master master)
  {
      if (pb->seekable & AVIO_SEEKABLE_NORMAL) {
  
          uint8_t *buf;
          int size = avio_get_dyn_buf(*dyn_cp, &buf);
  
          avio_write(pb, buf, size);
          end_ebml_master(pb, master);
      }
  }
  
  static void put_xiph_size(AVIOContext *pb, int size)
  {
      ffio_fill(pb, 255, size / 255);
      avio_w8(pb, size % 255);
  }
  
  /**
   * Free the members allocated in the mux context.
   */
  static void mkv_free(MatroskaMuxContext *mkv) {
      uint8_t* buf;
      if (mkv->dyn_bc) {
          avio_close_dyn_buf(mkv->dyn_bc, &buf);
          av_free(buf);
      }
      if (mkv->info_bc) {
          avio_close_dyn_buf(mkv->info_bc, &buf);
          av_free(buf);
      }
      if (mkv->tracks_bc) {
          avio_close_dyn_buf(mkv->tracks_bc, &buf);
          av_free(buf);
      }
      if (mkv->tags_bc) {
          avio_close_dyn_buf(mkv->tags_bc, &buf);
          av_free(buf);
      }
      if (mkv->main_seekhead) {
          av_freep(&mkv->main_seekhead->entries);
          av_freep(&mkv->main_seekhead);
      }
      if (mkv->cues) {
          av_freep(&mkv->cues->entries);
          av_freep(&mkv->cues);
      }
      if (mkv->attachments) {
          av_freep(&mkv->attachments->entries);
          av_freep(&mkv->attachments);
      }
      av_freep(&mkv->tracks);
      av_freep(&mkv->stream_durations);
      av_freep(&mkv->stream_duration_offsets);
  }
  
  /**
   * Initialize a mkv_seekhead element to be ready to index level 1 Matroska
   * elements. If a maximum number of elements is specified, enough space
   * will be reserved at the current file location to write a seek head of
   * that size.
   *
   * @param segment_offset The absolute offset to the position in the file
   *                       where the segment begins.
   * @param numelements The maximum number of elements that will be indexed
   *                    by this seek head, 0 if unlimited.
   */
  static mkv_seekhead *mkv_start_seekhead(AVIOContext *pb, int64_t segment_offset,
                                          int numelements)
  {
      mkv_seekhead *new_seekhead = av_mallocz(sizeof(mkv_seekhead));
      if (!new_seekhead)
          return NULL;
  
      new_seekhead->segment_offset = segment_offset;
  
      if (numelements > 0) {
          new_seekhead->filepos = avio_tell(pb);
          // 21 bytes max for a seek entry, 10 bytes max for the SeekHead ID
          // and size, 6 bytes for a CRC32 element, and 3 bytes to guarantee
          // that an EBML void element will fit afterwards
          new_seekhead->reserved_size = numelements * MAX_SEEKENTRY_SIZE + 19;
          new_seekhead->max_entries   = numelements;
          put_ebml_void(pb, new_seekhead->reserved_size);
      }
      return new_seekhead;
  }
  
  static int mkv_add_seekhead_entry(mkv_seekhead *seekhead, unsigned int elementid, uint64_t filepos)
  {
      mkv_seekhead_entry *entries = seekhead->entries;
  
      // don't store more elements than we reserved space for
      if (seekhead->max_entries > 0 && seekhead->max_entries <= seekhead->num_entries)
          return -1;
  
      entries = av_realloc_array(entries, seekhead->num_entries + 1, sizeof(mkv_seekhead_entry));
      if (!entries)
          return AVERROR(ENOMEM);
      seekhead->entries = entries;
  
      seekhead->entries[seekhead->num_entries].elementid    = elementid;
      seekhead->entries[seekhead->num_entries++].segmentpos = filepos - seekhead->segment_offset;
  
      return 0;
  }
  
  /**
   * Write the seek head to the file and free it. If a maximum number of
   * elements was specified to mkv_start_seekhead(), the seek head will
   * be written at the location reserved for it. Otherwise, it is written
   * at the current location in the file.
   *
   * @return The file offset where the seekhead was written,
   * -1 if an error occurred.
   */
  static int64_t mkv_write_seekhead(AVIOContext *pb, MatroskaMuxContext *mkv)
  {
      AVIOContext *dyn_cp;
      mkv_seekhead *seekhead = mkv->main_seekhead;
      ebml_master metaseek, seekentry;
      int64_t currentpos;
      int i;
  
      currentpos = avio_tell(pb);
  
      if (seekhead->reserved_size > 0) {
          if (avio_seek(pb, seekhead->filepos, SEEK_SET) < 0) {
              currentpos = -1;
              goto fail;
          }
      }
  
      if (start_ebml_master_crc32(pb, &dyn_cp, mkv, &metaseek, MATROSKA_ID_SEEKHEAD,
                                  seekhead->reserved_size) < 0) {
          currentpos = -1;
          goto fail;
      }
  
      for (i = 0; i < seekhead->num_entries; i++) {
          mkv_seekhead_entry *entry = &seekhead->entries[i];
  
          seekentry = start_ebml_master(dyn_cp, MATROSKA_ID_SEEKENTRY, MAX_SEEKENTRY_SIZE);
  
          put_ebml_id(dyn_cp, MATROSKA_ID_SEEKID);
          put_ebml_num(dyn_cp, ebml_id_size(entry->elementid), 0);
          put_ebml_id(dyn_cp, entry->elementid);
  
          put_ebml_uint(dyn_cp, MATROSKA_ID_SEEKPOSITION, entry->segmentpos);
          end_ebml_master(dyn_cp, seekentry);
      }
      end_ebml_master_crc32(pb, &dyn_cp, mkv, metaseek);
  
      if (seekhead->reserved_size > 0) {
          uint64_t remaining = seekhead->filepos + seekhead->reserved_size - avio_tell(pb);
          put_ebml_void(pb, remaining);
          avio_seek(pb, currentpos, SEEK_SET);
  
          currentpos = seekhead->filepos;
      }
  fail:
      av_freep(&mkv->main_seekhead->entries);
      av_freep(&mkv->main_seekhead);
  
      return currentpos;
  }
  
  static mkv_cues *mkv_start_cues(int64_t segment_offset)
  {
      mkv_cues *cues = av_mallocz(sizeof(mkv_cues));
      if (!cues)
          return NULL;
  
      cues->segment_offset = segment_offset;
      return cues;
  }
  
  static int mkv_add_cuepoint(mkv_cues *cues, int stream, int tracknum, int64_t ts,
                              int64_t cluster_pos, int64_t relative_pos, int64_t duration)
  {
      mkv_cuepoint *entries = cues->entries;
  
      if (ts < 0)
          return 0;
  
      entries = av_realloc_array(entries, cues->num_entries + 1, sizeof(mkv_cuepoint));
      if (!entries)
          return AVERROR(ENOMEM);
      cues->entries = entries;
  
      cues->entries[cues->num_entries].pts           = ts;
      cues->entries[cues->num_entries].stream_idx    = stream;
      cues->entries[cues->num_entries].tracknum      = tracknum;
      cues->entries[cues->num_entries].cluster_pos   = cluster_pos - cues->segment_offset;
      cues->entries[cues->num_entries].relative_pos  = relative_pos;
      cues->entries[cues->num_entries++].duration    = duration;
  
      return 0;
  }
  
  static int64_t mkv_write_cues(AVFormatContext *s, mkv_cues *cues, mkv_track *tracks, int num_tracks)
  {
      MatroskaMuxContext *mkv = s->priv_data;
      AVIOContext *dyn_cp, *pb = s->pb;
      ebml_master cues_element;
      int64_t currentpos;
      int i, j, ret;
  
      currentpos = avio_tell(pb);
      ret = start_ebml_master_crc32(pb, &dyn_cp, mkv, &cues_element, MATROSKA_ID_CUES, 0);
      if (ret < 0)
          return ret;
  
      for (i = 0; i < cues->num_entries; i++) {
          ebml_master cuepoint, track_positions;
          mkv_cuepoint *entry = &cues->entries[i];
          uint64_t pts = entry->pts;
          int ctp_nb = 0;
  
          // Calculate the number of entries, so we know the element size
          for (j = 0; j < num_tracks; j++)
              tracks[j].has_cue = 0;
          for (j = 0; j < cues->num_entries - i && entry[j].pts == pts; j++) {
              int tracknum = entry[j].stream_idx;
              av_assert0(tracknum>=0 && tracknum<num_tracks);
              if (tracks[tracknum].has_cue && s->streams[tracknum]->codecpar->codec_type != AVMEDIA_TYPE_SUBTITLE)
                  continue;
              tracks[tracknum].has_cue = 1;
              ctp_nb ++;
          }
  
          cuepoint = start_ebml_master(dyn_cp, MATROSKA_ID_POINTENTRY, MAX_CUEPOINT_SIZE(ctp_nb));
          put_ebml_uint(dyn_cp, MATROSKA_ID_CUETIME, pts);
  
          // put all the entries from different tracks that have the exact same
          // timestamp into the same CuePoint
          for (j = 0; j < num_tracks; j++)
              tracks[j].has_cue = 0;
          for (j = 0; j < cues->num_entries - i && entry[j].pts == pts; j++) {
              int tracknum = entry[j].stream_idx;
              av_assert0(tracknum>=0 && tracknum<num_tracks);
              if (tracks[tracknum].has_cue && s->streams[tracknum]->codecpar->codec_type != AVMEDIA_TYPE_SUBTITLE)
                  continue;
              tracks[tracknum].has_cue = 1;
              track_positions = start_ebml_master(dyn_cp, MATROSKA_ID_CUETRACKPOSITION, MAX_CUETRACKPOS_SIZE);
              put_ebml_uint(dyn_cp, MATROSKA_ID_CUETRACK           , entry[j].tracknum   );
              put_ebml_uint(dyn_cp, MATROSKA_ID_CUECLUSTERPOSITION , entry[j].cluster_pos);
              put_ebml_uint(dyn_cp, MATROSKA_ID_CUERELATIVEPOSITION, entry[j].relative_pos);
              if (entry[j].duration != -1)
                  put_ebml_uint(dyn_cp, MATROSKA_ID_CUEDURATION    , entry[j].duration);
              end_ebml_master(dyn_cp, track_positions);
          }
          i += j - 1;
          end_ebml_master(dyn_cp, cuepoint);
      }
      end_ebml_master_crc32(pb, &dyn_cp, mkv, cues_element);
  
      return currentpos;
  }
  
  static int put_xiph_codecpriv(AVFormatContext *s, AVIOContext *pb, AVCodecParameters *par)
  {
      const uint8_t *header_start[3];
      int header_len[3];
      int first_header_size;
      int j;
  
      if (par->codec_id == AV_CODEC_ID_VORBIS)
          first_header_size = 30;
      else
          first_header_size = 42;
  
      if (avpriv_split_xiph_headers(par->extradata, par->extradata_size,
                                first_header_size, header_start, header_len) < 0) {
          av_log(s, AV_LOG_ERROR, "Extradata corrupt.\n");
          return -1;
      }
  
      avio_w8(pb, 2);                    // number packets - 1
      for (j = 0; j < 2; j++) {
          put_xiph_size(pb, header_len[j]);
      }
      for (j = 0; j < 3; j++)
          avio_write(pb, header_start[j], header_len[j]);
  
      return 0;
  }
  
  static int put_wv_codecpriv(AVIOContext *pb, AVCodecParameters *par)
  {
      if (par->extradata && par->extradata_size == 2)
          avio_write(pb, par->extradata, 2);
      else
          avio_wl16(pb, 0x403); // fallback to the version mentioned in matroska specs
      return 0;
  }
  
  static int put_flac_codecpriv(AVFormatContext *s,
                                AVIOContext *pb, AVCodecParameters *par)
  {
      int write_comment = (par->channel_layout &&
                           !(par->channel_layout & ~0x3ffffULL) &&
                           !ff_flac_is_native_layout(par->channel_layout));
      int ret = ff_flac_write_header(pb, par->extradata, par->extradata_size,
                                     !write_comment);
  
      if (ret < 0)
          return ret;
  
      if (write_comment) {
          const char *vendor = (s->flags & AVFMT_FLAG_BITEXACT) ?
                               "Lavf" : LIBAVFORMAT_IDENT;
          AVDictionary *dict = NULL;
          uint8_t buf[32], *data, *p;
          int64_t len;
  
          snprintf(buf, sizeof(buf), "0x%"PRIx64, par->channel_layout);
          av_dict_set(&dict, "WAVEFORMATEXTENSIBLE_CHANNEL_MASK", buf, 0);
  
          len = ff_vorbiscomment_length(dict, vendor);
          if (len >= ((1<<24) - 4))
              return AVERROR(EINVAL);
  
          data = av_malloc(len + 4);
          if (!data) {
              av_dict_free(&dict);
              return AVERROR(ENOMEM);
          }
  
          data[0] = 0x84;
          AV_WB24(data + 1, len);
  
          p = data + 4;
          ff_vorbiscomment_write(&p, &dict, vendor);
  
          avio_write(pb, data, len + 4);
  
          av_freep(&data);
          av_dict_free(&dict);
      }
  
      return 0;
  }
  
  static int get_aac_sample_rates(AVFormatContext *s, uint8_t *extradata, int extradata_size,
                                  int *sample_rate, int *output_sample_rate)
  {
      MPEG4AudioConfig mp4ac;
      int ret;
  
      ret = avpriv_mpeg4audio_get_config(&mp4ac, extradata,
                                         extradata_size * 8, 1);
      /* Don't abort if the failure is because of missing extradata. Assume in that
       * case a bitstream filter will provide the muxer with the extradata in the
       * first packet.
       * Abort however if s->pb is not seekable, as we would not be able to seek back
       * to write the sample rate elements once the extradata shows up, anyway. */
      if (ret < 0 && (extradata_size || !(s->pb->seekable & AVIO_SEEKABLE_NORMAL))) {
          av_log(s, AV_LOG_ERROR,
                 "Error parsing AAC extradata, unable to determine samplerate.\n");
          return AVERROR(EINVAL);
      }
  
      if (ret < 0) {
          /* This will only happen when this function is called while writing the
           * header and no extradata is available. The space for this element has
           * to be reserved for when this function is called again after the
           * extradata shows up in the first packet, as there's no way to know if
           * output_sample_rate will be different than sample_rate or not. */
          *output_sample_rate = *sample_rate;
      } else {
          *sample_rate        = mp4ac.sample_rate;
          *output_sample_rate = mp4ac.ext_sample_rate;
      }
      return 0;
  }
  
  static int mkv_write_native_codecprivate(AVFormatContext *s, AVIOContext *pb,
                                           AVCodecParameters *par,
                                           AVIOContext *dyn_cp)
  {
      switch (par->codec_id) {
      case AV_CODEC_ID_VORBIS:
      case AV_CODEC_ID_THEORA:
          return put_xiph_codecpriv(s, dyn_cp, par);
      case AV_CODEC_ID_FLAC:
          return put_flac_codecpriv(s, dyn_cp, par);
      case AV_CODEC_ID_WAVPACK:
          return put_wv_codecpriv(dyn_cp, par);
      case AV_CODEC_ID_H264:
          return ff_isom_write_avcc(dyn_cp, par->extradata,
                                    par->extradata_size);
      case AV_CODEC_ID_HEVC:
          ff_isom_write_hvcc(dyn_cp, par->extradata,
                             par->extradata_size, 0);
          return 0;
      case AV_CODEC_ID_ALAC:
          if (par->extradata_size < 36) {
              av_log(s, AV_LOG_ERROR,
                     "Invalid extradata found, ALAC expects a 36-byte "
                     "QuickTime atom.");
              return AVERROR_INVALIDDATA;
          } else
              avio_write(dyn_cp, par->extradata + 12,
                         par->extradata_size - 12);
          break;
      case AV_CODEC_ID_AAC:
          if (par->extradata_size)
              avio_write(dyn_cp, par->extradata, par->extradata_size);
          else
              put_ebml_void(pb, MAX_PCE_SIZE + 2 + 4);
          break;
      default:
          if (par->codec_id == AV_CODEC_ID_PRORES &&
              ff_codec_get_id(ff_codec_movvideo_tags, par->codec_tag) == AV_CODEC_ID_PRORES) {
              avio_wl32(dyn_cp, par->codec_tag);
          } else if (par->extradata_size && par->codec_id != AV_CODEC_ID_TTA)
              avio_write(dyn_cp, par->extradata, par->extradata_size);
      }
  
      return 0;
  }
  
  static int mkv_write_codecprivate(AVFormatContext *s, AVIOContext *pb,
                                    AVCodecParameters *par,
                                    int native_id, int qt_id)
  {
      AVIOContext *dyn_cp;
      uint8_t *codecpriv;
      int ret, codecpriv_size;
  
      ret = avio_open_dyn_buf(&dyn_cp);
      if (ret < 0)
          return ret;
  
      if (native_id) {
          ret = mkv_write_native_codecprivate(s, pb, par, dyn_cp);
      } else if (par->codec_type == AVMEDIA_TYPE_VIDEO) {
          if (qt_id) {
              if (!par->codec_tag)
                  par->codec_tag = ff_codec_get_tag(ff_codec_movvideo_tags,
                                                      par->codec_id);
              if (   ff_codec_get_id(ff_codec_movvideo_tags, par->codec_tag) == par->codec_id
                  && (!par->extradata_size || ff_codec_get_id(ff_codec_movvideo_tags, AV_RL32(par->extradata + 4)) != par->codec_id)
              ) {
                  int i;
                  avio_wb32(dyn_cp, 0x5a + par->extradata_size);
                  avio_wl32(dyn_cp, par->codec_tag);
                  for(i = 0; i < 0x5a - 8; i++)
                      avio_w8(dyn_cp, 0);
              }
              avio_write(dyn_cp, par->extradata, par->extradata_size);
          } else {
              if (!ff_codec_get_tag(ff_codec_bmp_tags, par->codec_id))
                  av_log(s, AV_LOG_WARNING, "codec %s is not supported by this format\n",
                         avcodec_get_name(par->codec_id));
  
              if (!par->codec_tag)
                  par->codec_tag = ff_codec_get_tag(ff_codec_bmp_tags,
                                                    par->codec_id);
              if (!par->codec_tag && par->codec_id != AV_CODEC_ID_RAWVIDEO) {
                  av_log(s, AV_LOG_ERROR, "No bmp codec tag found for codec %s\n",
                         avcodec_get_name(par->codec_id));
                  ret = AVERROR(EINVAL);
              }
  
              ff_put_bmp_header(dyn_cp, par, 0, 0);
          }
      } else if (par->codec_type == AVMEDIA_TYPE_AUDIO) {
          unsigned int tag;
          tag = ff_codec_get_tag(ff_codec_wav_tags, par->codec_id);
          if (!tag) {
              av_log(s, AV_LOG_ERROR, "No wav codec tag found for codec %s\n",
                     avcodec_get_name(par->codec_id));
              ret = AVERROR(EINVAL);
          }
          if (!par->codec_tag)
              par->codec_tag = tag;
  
          ff_put_wav_header(s, dyn_cp, par, FF_PUT_WAV_HEADER_FORCE_WAVEFORMATEX);
      }
  
      codecpriv_size = avio_close_dyn_buf(dyn_cp, &codecpriv);
      if (codecpriv_size)
          put_ebml_binary(pb, MATROSKA_ID_CODECPRIVATE, codecpriv,
                          codecpriv_size);
      av_free(codecpriv);
      return ret;
  }
  
  static int mkv_write_video_color(AVIOContext *pb, AVCodecParameters *par, AVStream *st) {
      AVIOContext *dyn_cp;
      uint8_t *colorinfo_ptr;
      int side_data_size = 0;
      int ret, colorinfo_size;
      const uint8_t *side_data;
  
      ret = avio_open_dyn_buf(&dyn_cp);
      if (ret < 0)
          return ret;
  
      if (par->color_trc != AVCOL_TRC_UNSPECIFIED &&
          par->color_trc < AVCOL_TRC_NB) {
          put_ebml_uint(dyn_cp, MATROSKA_ID_VIDEOCOLORTRANSFERCHARACTERISTICS,
                        par->color_trc);
      }
      if (par->color_space != AVCOL_SPC_UNSPECIFIED &&
          par->color_space < AVCOL_SPC_NB) {
          put_ebml_uint(dyn_cp, MATROSKA_ID_VIDEOCOLORMATRIXCOEFF, par->color_space);
      }
      if (par->color_primaries != AVCOL_PRI_UNSPECIFIED &&
          par->color_primaries < AVCOL_PRI_NB) {
          put_ebml_uint(dyn_cp, MATROSKA_ID_VIDEOCOLORPRIMARIES, par->color_primaries);
      }
      if (par->color_range != AVCOL_RANGE_UNSPECIFIED &&
          par->color_range < AVCOL_RANGE_NB) {
          put_ebml_uint(dyn_cp, MATROSKA_ID_VIDEOCOLORRANGE, par->color_range);
      }
      if (par->chroma_location != AVCHROMA_LOC_UNSPECIFIED &&
          par->chroma_location <= AVCHROMA_LOC_TOP) {
          int xpos, ypos;
  
          avcodec_enum_to_chroma_pos(&xpos, &ypos, par->chroma_location);
          put_ebml_uint(dyn_cp, MATROSKA_ID_VIDEOCOLORCHROMASITINGHORZ, (xpos >> 7) + 1);
          put_ebml_uint(dyn_cp, MATROSKA_ID_VIDEOCOLORCHROMASITINGVERT, (ypos >> 7) + 1);
      }
  
      side_data = av_stream_get_side_data(st, AV_PKT_DATA_CONTENT_LIGHT_LEVEL,
                                          &side_data_size);
      if (side_data_size) {
          const AVContentLightMetadata *metadata =
              (const AVContentLightMetadata*)side_data;
          put_ebml_uint(dyn_cp, MATROSKA_ID_VIDEOCOLORMAXCLL,  metadata->MaxCLL);
          put_ebml_uint(dyn_cp, MATROSKA_ID_VIDEOCOLORMAXFALL, metadata->MaxFALL);
      }
  
      side_data = av_stream_get_side_data(st, AV_PKT_DATA_MASTERING_DISPLAY_METADATA,
                                          &side_data_size);
      if (side_data_size == sizeof(AVMasteringDisplayMetadata)) {
          ebml_master meta_element = start_ebml_master(
              dyn_cp, MATROSKA_ID_VIDEOCOLORMASTERINGMETA, 0);
          const AVMasteringDisplayMetadata *metadata =
              (const AVMasteringDisplayMetadata*)side_data;
          if (metadata->has_primaries) {
              put_ebml_float(dyn_cp, MATROSKA_ID_VIDEOCOLOR_RX,
                             av_q2d(metadata->display_primaries[0][0]));
              put_ebml_float(dyn_cp, MATROSKA_ID_VIDEOCOLOR_RY,
                             av_q2d(metadata->display_primaries[0][1]));
              put_ebml_float(dyn_cp, MATROSKA_ID_VIDEOCOLOR_GX,
                             av_q2d(metadata->display_primaries[1][0]));
              put_ebml_float(dyn_cp, MATROSKA_ID_VIDEOCOLOR_GY,
                             av_q2d(metadata->display_primaries[1][1]));
              put_ebml_float(dyn_cp, MATROSKA_ID_VIDEOCOLOR_BX,
                             av_q2d(metadata->display_primaries[2][0]));
              put_ebml_float(dyn_cp, MATROSKA_ID_VIDEOCOLOR_BY,
                             av_q2d(metadata->display_primaries[2][1]));
              put_ebml_float(dyn_cp, MATROSKA_ID_VIDEOCOLOR_WHITEX,
                             av_q2d(metadata->white_point[0]));
              put_ebml_float(dyn_cp, MATROSKA_ID_VIDEOCOLOR_WHITEY,
                             av_q2d(metadata->white_point[1]));
          }
          if (metadata->has_luminance) {
              put_ebml_float(dyn_cp, MATROSKA_ID_VIDEOCOLOR_LUMINANCEMAX,
                             av_q2d(metadata->max_luminance));
              put_ebml_float(dyn_cp, MATROSKA_ID_VIDEOCOLOR_LUMINANCEMIN,
                             av_q2d(metadata->min_luminance));
          }
          end_ebml_master(dyn_cp, meta_element);
      }
  
      colorinfo_size = avio_close_dyn_buf(dyn_cp, &colorinfo_ptr);
      if (colorinfo_size) {
          ebml_master colorinfo = start_ebml_master(pb, MATROSKA_ID_VIDEOCOLOR, colorinfo_size);
          avio_write(pb, colorinfo_ptr, colorinfo_size);
          end_ebml_master(pb, colorinfo);
      }
      av_free(colorinfo_ptr);
      return 0;
  }
  
  static int mkv_write_video_projection(AVFormatContext *s, AVIOContext *pb,
                                        AVStream *st)
  {
      AVIOContext b;
      AVIOContext *dyn_cp;
      int side_data_size = 0;
      int ret, projection_size;
      uint8_t *projection_ptr;
      uint8_t private[20];
  
      const AVSphericalMapping *spherical =
          (const AVSphericalMapping *)av_stream_get_side_data(st, AV_PKT_DATA_SPHERICAL,
                                                              &side_data_size);
  
      if (!side_data_size)
          return 0;
  
      ret = avio_open_dyn_buf(&dyn_cp);
      if (ret < 0)
          return ret;
  
      switch (spherical->projection) {
      case AV_SPHERICAL_EQUIRECTANGULAR:
          put_ebml_uint(dyn_cp, MATROSKA_ID_VIDEOPROJECTIONTYPE,
                        MATROSKA_VIDEO_PROJECTION_TYPE_EQUIRECTANGULAR);
          break;
      case AV_SPHERICAL_EQUIRECTANGULAR_TILE:
          ffio_init_context(&b, private, 20, 1, NULL, NULL, NULL, NULL);
          put_ebml_uint(dyn_cp, MATROSKA_ID_VIDEOPROJECTIONTYPE,
                        MATROSKA_VIDEO_PROJECTION_TYPE_EQUIRECTANGULAR);
          avio_wb32(&b, 0); // version + flags
          avio_wb32(&b, spherical->bound_top);
          avio_wb32(&b, spherical->bound_bottom);
          avio_wb32(&b, spherical->bound_left);
          avio_wb32(&b, spherical->bound_right);
          put_ebml_binary(dyn_cp, MATROSKA_ID_VIDEOPROJECTIONPRIVATE,
                          private, avio_tell(&b));
          break;
      case AV_SPHERICAL_CUBEMAP:
          ffio_init_context(&b, private, 12, 1, NULL, NULL, NULL, NULL);
          put_ebml_uint(dyn_cp, MATROSKA_ID_VIDEOPROJECTIONTYPE,
                        MATROSKA_VIDEO_PROJECTION_TYPE_CUBEMAP);
          avio_wb32(&b, 0); // version + flags
          avio_wb32(&b, 0); // layout
          avio_wb32(&b, spherical->padding);
          put_ebml_binary(dyn_cp, MATROSKA_ID_VIDEOPROJECTIONPRIVATE,
                          private, avio_tell(&b));
          break;
      default:
          av_log(s, AV_LOG_WARNING, "Unknown projection type\n");
          goto end;
      }
  
      if (spherical->yaw)
          put_ebml_float(dyn_cp, MATROSKA_ID_VIDEOPROJECTIONPOSEYAW,
                         (double) spherical->yaw   / (1 << 16));
      if (spherical->pitch)
          put_ebml_float(dyn_cp, MATROSKA_ID_VIDEOPROJECTIONPOSEPITCH,
                         (double) spherical->pitch / (1 << 16));
      if (spherical->roll)
          put_ebml_float(dyn_cp, MATROSKA_ID_VIDEOPROJECTIONPOSEROLL,
                         (double) spherical->roll  / (1 << 16));
  
  end:
      projection_size = avio_close_dyn_buf(dyn_cp, &projection_ptr);
      if (projection_size) {
          ebml_master projection = start_ebml_master(pb,
                                                     MATROSKA_ID_VIDEOPROJECTION,
                                                     projection_size);
          avio_write(pb, projection_ptr, projection_size);
          end_ebml_master(pb, projection);
      }
      av_freep(&projection_ptr);
  
      return 0;
  }
  
  static void mkv_write_field_order(AVIOContext *pb, int mode,
                                    enum AVFieldOrder field_order)
  {
      switch (field_order) {
      case AV_FIELD_UNKNOWN:
          break;
      case AV_FIELD_PROGRESSIVE:
          put_ebml_uint(pb, MATROSKA_ID_VIDEOFLAGINTERLACED,
                        MATROSKA_VIDEO_INTERLACE_FLAG_PROGRESSIVE);
          break;
      case AV_FIELD_TT:
      case AV_FIELD_BB:
      case AV_FIELD_TB:
      case AV_FIELD_BT:
          put_ebml_uint(pb, MATROSKA_ID_VIDEOFLAGINTERLACED,
                        MATROSKA_VIDEO_INTERLACE_FLAG_INTERLACED);
          if (mode != MODE_WEBM) {
              switch (field_order) {
              case AV_FIELD_TT:
                  put_ebml_uint(pb, MATROSKA_ID_VIDEOFIELDORDER,
                                MATROSKA_VIDEO_FIELDORDER_TT);
                  break;
              case AV_FIELD_BB:
                  put_ebml_uint(pb, MATROSKA_ID_VIDEOFIELDORDER,
                                MATROSKA_VIDEO_FIELDORDER_BB);
                  break;
              case AV_FIELD_TB:
                  put_ebml_uint(pb, MATROSKA_ID_VIDEOFIELDORDER,
                                MATROSKA_VIDEO_FIELDORDER_TB);
                  break;
              case AV_FIELD_BT:
                  put_ebml_uint(pb, MATROSKA_ID_VIDEOFIELDORDER,
                                MATROSKA_VIDEO_FIELDORDER_BT);
                  break;
              }
          }
      }
  }
  
  static int mkv_write_stereo_mode(AVFormatContext *s, AVIOContext *pb,
                                   AVStream *st, int mode, int *h_width, int *h_height)
  {
      int i;
      int ret = 0;
      AVDictionaryEntry *tag;
      MatroskaVideoStereoModeType format = MATROSKA_VIDEO_STEREOMODE_TYPE_NB;
  
      *h_width = 1;
      *h_height = 1;
      // convert metadata into proper side data and add it to the stream
      if ((tag = av_dict_get(st->metadata, "stereo_mode", NULL, 0)) ||
          (tag = av_dict_get( s->metadata, "stereo_mode", NULL, 0))) {
          int stereo_mode = atoi(tag->value);
  
          for (i=0; i<MATROSKA_VIDEO_STEREOMODE_TYPE_NB; i++)
              if (!strcmp(tag->value, ff_matroska_video_stereo_mode[i])){
                  stereo_mode = i;
                  break;
              }
  
          if (stereo_mode < MATROSKA_VIDEO_STEREOMODE_TYPE_NB &&
              stereo_mode != 10 && stereo_mode != 12) {
              int ret = ff_mkv_stereo3d_conv(st, stereo_mode);
              if (ret < 0)
                  return ret;
          }
      }
  
      // iterate to find the stereo3d side data
      for (i = 0; i < st->nb_side_data; i++) {
          AVPacketSideData sd = st->side_data[i];
          if (sd.type == AV_PKT_DATA_STEREO3D) {
              AVStereo3D *stereo = (AVStereo3D *)sd.data;
  
              switch (stereo->type) {
              case AV_STEREO3D_2D:
                  format = MATROSKA_VIDEO_STEREOMODE_TYPE_MONO;
                  break;
              case AV_STEREO3D_SIDEBYSIDE:
                  format = (stereo->flags & AV_STEREO3D_FLAG_INVERT)
                      ? MATROSKA_VIDEO_STEREOMODE_TYPE_RIGHT_LEFT
                      : MATROSKA_VIDEO_STEREOMODE_TYPE_LEFT_RIGHT;
                  *h_width = 2;
                  break;
              case AV_STEREO3D_TOPBOTTOM:
                  format = MATROSKA_VIDEO_STEREOMODE_TYPE_TOP_BOTTOM;
                  if (stereo->flags & AV_STEREO3D_FLAG_INVERT)
                      format--;
                  *h_height = 2;
                  break;
              case AV_STEREO3D_CHECKERBOARD:
                  format = MATROSKA_VIDEO_STEREOMODE_TYPE_CHECKERBOARD_LR;
                  if (stereo->flags & AV_STEREO3D_FLAG_INVERT)
                      format--;
                  break;
              case AV_STEREO3D_LINES:
                  format = MATROSKA_VIDEO_STEREOMODE_TYPE_ROW_INTERLEAVED_LR;
                  if (stereo->flags & AV_STEREO3D_FLAG_INVERT)
                      format--;
                  *h_height = 2;
                  break;
              case AV_STEREO3D_COLUMNS:
                  format = MATROSKA_VIDEO_STEREOMODE_TYPE_COL_INTERLEAVED_LR;
                  if (stereo->flags & AV_STEREO3D_FLAG_INVERT)
                      format--;
                  *h_width = 2;
                  break;
              case AV_STEREO3D_FRAMESEQUENCE:
                  format = MATROSKA_VIDEO_STEREOMODE_TYPE_BOTH_EYES_BLOCK_LR;
                  if (stereo->flags & AV_STEREO3D_FLAG_INVERT)
                      format++;
                  break;
              }
              break;
          }
      }
  
      if (format == MATROSKA_VIDEO_STEREOMODE_TYPE_NB)
          return ret;
  
      // if webm, do not write unsupported modes
      if ((mode == MODE_WEBM &&
          format > MATROSKA_VIDEO_STEREOMODE_TYPE_TOP_BOTTOM &&
          format != MATROSKA_VIDEO_STEREOMODE_TYPE_RIGHT_LEFT)
          || format >= MATROSKA_VIDEO_STEREOMODE_TYPE_NB) {
          av_log(s, AV_LOG_ERROR,
                 "The specified stereo mode is not valid.\n");
          format = MATROSKA_VIDEO_STEREOMODE_TYPE_NB;
          return AVERROR(EINVAL);
      }
  
      // write StereoMode if format is valid
      put_ebml_uint(pb, MATROSKA_ID_VIDEOSTEREOMODE, format);
  
      return ret;
  }
  
  static int mkv_write_track(AVFormatContext *s, MatroskaMuxContext *mkv,
                             int i, AVIOContext *pb, int default_stream_exists)
  {
      AVStream *st = s->streams[i];
      AVCodecParameters *par = st->codecpar;
      ebml_master subinfo, track;
      int native_id = 0;
      int qt_id = 0;
      int bit_depth = av_get_bits_per_sample(par->codec_id);
      int sample_rate = par->sample_rate;
      int output_sample_rate = 0;
      int display_width_div = 1;
      int display_height_div = 1;
      int j, ret;
      AVDictionaryEntry *tag;
  
      if (par->codec_type == AVMEDIA_TYPE_ATTACHMENT) {
          mkv->have_attachments = 1;
          return 0;
      }
  
      if (par->codec_type == AVMEDIA_TYPE_AUDIO) {
          if (!bit_depth && par->codec_id != AV_CODEC_ID_ADPCM_G726) {
              if (par->bits_per_raw_sample)
                  bit_depth = par->bits_per_raw_sample;
              else
                  bit_depth = av_get_bytes_per_sample(par->format) << 3;
          }
          if (!bit_depth)
              bit_depth = par->bits_per_coded_sample;
      }
  
      if (par->codec_id == AV_CODEC_ID_AAC) {
          ret = get_aac_sample_rates(s, par->extradata, par->extradata_size, &sample_rate,
                                     &output_sample_rate);
          if (ret < 0)
              return ret;
      }
  
      track = start_ebml_master(pb, MATROSKA_ID_TRACKENTRY, 0);
      put_ebml_uint (pb, MATROSKA_ID_TRACKNUMBER,
                     mkv->is_dash ? mkv->dash_track_number : i + 1);
      put_ebml_uint (pb, MATROSKA_ID_TRACKUID,
                     mkv->is_dash ? mkv->dash_track_number : i + 1);
      put_ebml_uint (pb, MATROSKA_ID_TRACKFLAGLACING , 0);    // no lacing (yet)
  
      if ((tag = av_dict_get(st->metadata, "title", NULL, 0)))
          put_ebml_string(pb, MATROSKA_ID_TRACKNAME, tag->value);
      tag = av_dict_get(st->metadata, "language", NULL, 0);
      if (mkv->mode != MODE_WEBM || par->codec_id != AV_CODEC_ID_WEBVTT) {
          put_ebml_string(pb, MATROSKA_ID_TRACKLANGUAGE, tag && tag->value ? tag->value:"und");
      } else if (tag && tag->value) {
          put_ebml_string(pb, MATROSKA_ID_TRACKLANGUAGE, tag->value);
      }
  
      // The default value for TRACKFLAGDEFAULT is 1, so add element
      // if we need to clear it.
      if (default_stream_exists && !(st->disposition & AV_DISPOSITION_DEFAULT))
          put_ebml_uint(pb, MATROSKA_ID_TRACKFLAGDEFAULT, !!(st->disposition & AV_DISPOSITION_DEFAULT));
  
      if (st->disposition & AV_DISPOSITION_FORCED)
          put_ebml_uint(pb, MATROSKA_ID_TRACKFLAGFORCED, 1);
  
      if (mkv->mode == MODE_WEBM && par->codec_id == AV_CODEC_ID_WEBVTT) {
          const char *codec_id;
          if (st->disposition & AV_DISPOSITION_CAPTIONS) {
              codec_id = "D_WEBVTT/CAPTIONS";
              native_id = MATROSKA_TRACK_TYPE_SUBTITLE;
          } else if (st->disposition & AV_DISPOSITION_DESCRIPTIONS) {
              codec_id = "D_WEBVTT/DESCRIPTIONS";
              native_id = MATROSKA_TRACK_TYPE_METADATA;
          } else if (st->disposition & AV_DISPOSITION_METADATA) {
              codec_id = "D_WEBVTT/METADATA";
              native_id = MATROSKA_TRACK_TYPE_METADATA;
          } else {
              codec_id = "D_WEBVTT/SUBTITLES";
              native_id = MATROSKA_TRACK_TYPE_SUBTITLE;
          }
          put_ebml_string(pb, MATROSKA_ID_CODECID, codec_id);
      } else {
          // look for a codec ID string specific to mkv to use,
          // if none are found, use AVI codes
          if (par->codec_id != AV_CODEC_ID_RAWVIDEO || par->codec_tag) {
              for (j = 0; ff_mkv_codec_tags[j].id != AV_CODEC_ID_NONE; j++) {
                  if (ff_mkv_codec_tags[j].id == par->codec_id && par->codec_id != AV_CODEC_ID_FFV1) {
                      put_ebml_string(pb, MATROSKA_ID_CODECID, ff_mkv_codec_tags[j].str);
                      native_id = 1;
                      break;
                  }
              }
          } else {
              if (mkv->allow_raw_vfw) {
                  native_id = 0;
              } else {
                  av_log(s, AV_LOG_ERROR, "Raw RGB is not supported Natively in Matroska, you can use AVI or NUT or\n"
                                          "If you would like to store it anyway using VFW mode, enable allow_raw_vfw (-allow_raw_vfw 1)\n");
                  return AVERROR(EINVAL);
              }
          }
      }
  
      if (par->codec_type == AVMEDIA_TYPE_AUDIO && par->initial_padding && par->codec_id == AV_CODEC_ID_OPUS) {
          int64_t codecdelay = av_rescale_q(par->initial_padding,
                                            (AVRational){ 1, 48000 },
                                            (AVRational){ 1, 1000000000 });
          if (codecdelay < 0) {
              av_log(s, AV_LOG_ERROR, "Initial padding is invalid\n");
              return AVERROR(EINVAL);
          }
  //         mkv->tracks[i].ts_offset = av_rescale_q(par->initial_padding,
  //                                                 (AVRational){ 1, par->sample_rate },
  //                                                 st->time_base);
  
          put_ebml_uint(pb, MATROSKA_ID_CODECDELAY, codecdelay);
      }
      if (par->codec_id == AV_CODEC_ID_OPUS) {
          put_ebml_uint(pb, MATROSKA_ID_SEEKPREROLL, OPUS_SEEK_PREROLL);
      }
  
      if (mkv->mode == MODE_WEBM && !(par->codec_id == AV_CODEC_ID_VP8 ||
                                      par->codec_id == AV_CODEC_ID_VP9 ||
                                      par->codec_id == AV_CODEC_ID_OPUS ||
                                      par->codec_id == AV_CODEC_ID_VORBIS ||
                                      par->codec_id == AV_CODEC_ID_WEBVTT)) {
          av_log(s, AV_LOG_ERROR,
                 "Only VP8 or VP9 video and Vorbis or Opus audio and WebVTT subtitles are supported for WebM.\n");
          return AVERROR(EINVAL);
      }
  
      switch (par->codec_type) {
      case AVMEDIA_TYPE_VIDEO:
          mkv->have_video = 1;
          put_ebml_uint(pb, MATROSKA_ID_TRACKTYPE, MATROSKA_TRACK_TYPE_VIDEO);
  
          if(   st->avg_frame_rate.num > 0 && st->avg_frame_rate.den > 0
             && av_cmp_q(av_inv_q(st->avg_frame_rate), st->time_base) > 0)
              put_ebml_uint(pb, MATROSKA_ID_TRACKDEFAULTDURATION, 1000000000LL * st->avg_frame_rate.den / st->avg_frame_rate.num);
  
          if (!native_id &&
              ff_codec_get_tag(ff_codec_movvideo_tags, par->codec_id) &&
              ((!ff_codec_get_tag(ff_codec_bmp_tags,   par->codec_id) && par->codec_id != AV_CODEC_ID_RAWVIDEO) ||
               par->codec_id == AV_CODEC_ID_SVQ1 ||
               par->codec_id == AV_CODEC_ID_SVQ3 ||
               par->codec_id == AV_CODEC_ID_CINEPAK))
              qt_id = 1;
  
          if (qt_id)
              put_ebml_string(pb, MATROSKA_ID_CODECID, "V_QUICKTIME");
          else if (!native_id) {
              // if there is no mkv-specific codec ID, use VFW mode
              put_ebml_string(pb, MATROSKA_ID_CODECID, "V_MS/VFW/FOURCC");
              mkv->tracks[i].write_dts = 1;
              s->internal->avoid_negative_ts_use_pts = 0;
          }
  
          subinfo = start_ebml_master(pb, MATROSKA_ID_TRACKVIDEO, 0);
  
          put_ebml_uint (pb, MATROSKA_ID_VIDEOPIXELWIDTH , par->width);
          put_ebml_uint (pb, MATROSKA_ID_VIDEOPIXELHEIGHT, par->height);
  
          mkv_write_field_order(pb, mkv->mode, par->field_order);
  
          // check both side data and metadata for stereo information,
          // write the result to the bitstream if any is found
          ret = mkv_write_stereo_mode(s, pb, st, mkv->mode,
                                      &display_width_div,
                                      &display_height_div);
          if (ret < 0)
              return ret;
  
          if (((tag = av_dict_get(st->metadata, "alpha_mode", NULL, 0)) && atoi(tag->value)) ||
              ((tag = av_dict_get( s->metadata, "alpha_mode", NULL, 0)) && atoi(tag->value)) ||
              (par->format == AV_PIX_FMT_YUVA420P)) {
              put_ebml_uint(pb, MATROSKA_ID_VIDEOALPHAMODE, 1);
          }
  
          // write DisplayWidth and DisplayHeight, they contain the size of
          // a single source view and/or the display aspect ratio
          if (st->sample_aspect_ratio.num) {
              int64_t d_width = av_rescale(par->width, st->sample_aspect_ratio.num, st->sample_aspect_ratio.den);
              if (d_width > INT_MAX) {
                  av_log(s, AV_LOG_ERROR, "Overflow in display width\n");
                  return AVERROR(EINVAL);
              }
              if (d_width != par->width || display_width_div != 1 || display_height_div != 1) {
                  if (mkv->mode == MODE_WEBM || display_width_div != 1 || display_height_div != 1) {
                      put_ebml_uint(pb, MATROSKA_ID_VIDEODISPLAYWIDTH , d_width / display_width_div);
                      put_ebml_uint(pb, MATROSKA_ID_VIDEODISPLAYHEIGHT, par->height / display_height_div);
                  } else {
                      AVRational display_aspect_ratio;
                      av_reduce(&display_aspect_ratio.num, &display_aspect_ratio.den,
                                par->width  * (int64_t)st->sample_aspect_ratio.num,
                                par->height * (int64_t)st->sample_aspect_ratio.den,
                                1024 * 1024);
                      put_ebml_uint(pb, MATROSKA_ID_VIDEODISPLAYWIDTH,  display_aspect_ratio.num);
                      put_ebml_uint(pb, MATROSKA_ID_VIDEODISPLAYHEIGHT, display_aspect_ratio.den);
                      put_ebml_uint(pb, MATROSKA_ID_VIDEODISPLAYUNIT, MATROSKA_VIDEO_DISPLAYUNIT_DAR);
                  }
              }
          } else if (display_width_div != 1 || display_height_div != 1) {
              put_ebml_uint(pb, MATROSKA_ID_VIDEODISPLAYWIDTH , par->width / display_width_div);
              put_ebml_uint(pb, MATROSKA_ID_VIDEODISPLAYHEIGHT, par->height / display_height_div);
          } else if (mkv->mode != MODE_WEBM)
              put_ebml_uint(pb, MATROSKA_ID_VIDEODISPLAYUNIT, MATROSKA_VIDEO_DISPLAYUNIT_UNKNOWN);
  
          if (par->codec_id == AV_CODEC_ID_RAWVIDEO) {
              uint32_t color_space = av_le2ne32(par->codec_tag);
              put_ebml_binary(pb, MATROSKA_ID_VIDEOCOLORSPACE, &color_space, sizeof(color_space));
          }
          ret = mkv_write_video_color(pb, par, st);
          if (ret < 0)
              return ret;
          ret = mkv_write_video_projection(s, pb, st);
          if (ret < 0)
              return ret;
          end_ebml_master(pb, subinfo);
          break;
  
      case AVMEDIA_TYPE_AUDIO:
          put_ebml_uint(pb, MATROSKA_ID_TRACKTYPE, MATROSKA_TRACK_TYPE_AUDIO);
  
          if (!native_id)
              // no mkv-specific ID, use ACM mode
              put_ebml_string(pb, MATROSKA_ID_CODECID, "A_MS/ACM");
  
          subinfo = start_ebml_master(pb, MATROSKA_ID_TRACKAUDIO, 0);
          put_ebml_uint  (pb, MATROSKA_ID_AUDIOCHANNELS    , par->channels);
  
          mkv->tracks[i].sample_rate_offset = avio_tell(pb);
          put_ebml_float (pb, MATROSKA_ID_AUDIOSAMPLINGFREQ, sample_rate);
          if (output_sample_rate)
              put_ebml_float(pb, MATROSKA_ID_AUDIOOUTSAMPLINGFREQ, output_sample_rate);
          if (bit_depth)
              put_ebml_uint(pb, MATROSKA_ID_AUDIOBITDEPTH, bit_depth);
          end_ebml_master(pb, subinfo);
          break;
  
      case AVMEDIA_TYPE_SUBTITLE:
          if (!native_id) {
              av_log(s, AV_LOG_ERROR, "Subtitle codec %d is not supported.\n", par->codec_id);
              return AVERROR(ENOSYS);
          }
  
          if (mkv->mode != MODE_WEBM || par->codec_id != AV_CODEC_ID_WEBVTT)
              native_id = MATROSKA_TRACK_TYPE_SUBTITLE;
  
          put_ebml_uint(pb, MATROSKA_ID_TRACKTYPE, native_id);
          break;
      default:
          av_log(s, AV_LOG_ERROR, "Only audio, video, and subtitles are supported for Matroska.\n");
          return AVERROR(EINVAL);
      }
  
      if (mkv->mode != MODE_WEBM || par->codec_id != AV_CODEC_ID_WEBVTT) {
          mkv->tracks[i].codecpriv_offset = avio_tell(pb);
          ret = mkv_write_codecprivate(s, pb, par, native_id, qt_id);
          if (ret < 0)
              return ret;
      }
  
      end_ebml_master(pb, track);
  
      return 0;
  }
  
  static int mkv_write_tracks(AVFormatContext *s)
  {
      MatroskaMuxContext *mkv = s->priv_data;
      AVIOContext *pb = s->pb;
      int i, ret, default_stream_exists = 0;
  
      ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_TRACKS, avio_tell(pb));
      if (ret < 0)
          return ret;
  
      ret = start_ebml_master_crc32(pb, &mkv->tracks_bc, mkv, &mkv->tracks_master, MATROSKA_ID_TRACKS, 0);
      if (ret < 0)
          return ret;
  
      for (i = 0; i < s->nb_streams; i++) {
          AVStream *st = s->streams[i];
          default_stream_exists |= st->disposition & AV_DISPOSITION_DEFAULT;
      }
      for (i = 0; i < s->nb_streams; i++) {
          ret = mkv_write_track(s, mkv, i, mkv->tracks_bc, default_stream_exists);
          if (ret < 0)
              return ret;
      }
  
      if ((pb->seekable & AVIO_SEEKABLE_NORMAL) && !mkv->is_live)
          end_ebml_master_crc32_preliminary(pb, &mkv->tracks_bc, mkv, mkv->tracks_master);
      else
          end_ebml_master_crc32(pb, &mkv->tracks_bc, mkv, mkv->tracks_master);
  
      return 0;
  }
  
  static int mkv_write_chapters(AVFormatContext *s)
  {
      MatroskaMuxContext *mkv = s->priv_data;
      AVIOContext *dyn_cp, *pb = s->pb;
      ebml_master chapters, editionentry;
      AVRational scale = {1, 1E9};
      int i, ret;
  
      if (!s->nb_chapters || mkv->wrote_chapters)
          return 0;
  
      ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_CHAPTERS, avio_tell(pb));
      if (ret < 0) return ret;
  
      ret = start_ebml_master_crc32(pb, &dyn_cp, mkv, &chapters, MATROSKA_ID_CHAPTERS, 0);
      if (ret < 0) return ret;
  
      editionentry = start_ebml_master(dyn_cp, MATROSKA_ID_EDITIONENTRY, 0);
      if (mkv->mode != MODE_WEBM) {
          put_ebml_uint(dyn_cp, MATROSKA_ID_EDITIONFLAGDEFAULT, 1);
          put_ebml_uint(dyn_cp, MATROSKA_ID_EDITIONFLAGHIDDEN , 0);
      }
      for (i = 0; i < s->nb_chapters; i++) {
          ebml_master chapteratom, chapterdisplay;
          AVChapter *c     = s->chapters[i];
          int64_t chapterstart = av_rescale_q(c->start, c->time_base, scale);
          int64_t chapterend   = av_rescale_q(c->end,   c->time_base, scale);
          AVDictionaryEntry *t = NULL;
          if (chapterstart < 0 || chapterstart > chapterend || chapterend < 0) {
              av_log(s, AV_LOG_ERROR,
                     "Invalid chapter start (%"PRId64") or end (%"PRId64").\n",
                     chapterstart, chapterend);
              return AVERROR_INVALIDDATA;
          }
  
          chapteratom = start_ebml_master(dyn_cp, MATROSKA_ID_CHAPTERATOM, 0);
          put_ebml_uint(dyn_cp, MATROSKA_ID_CHAPTERUID, c->id + mkv->chapter_id_offset);
          put_ebml_uint(dyn_cp, MATROSKA_ID_CHAPTERTIMESTART, chapterstart);
          put_ebml_uint(dyn_cp, MATROSKA_ID_CHAPTERTIMEEND, chapterend);
          if (mkv->mode != MODE_WEBM) {
              put_ebml_uint(dyn_cp, MATROSKA_ID_CHAPTERFLAGHIDDEN , 0);
              put_ebml_uint(dyn_cp, MATROSKA_ID_CHAPTERFLAGENABLED, 1);
          }
          if ((t = av_dict_get(c->metadata, "title", NULL, 0))) {
              chapterdisplay = start_ebml_master(dyn_cp, MATROSKA_ID_CHAPTERDISPLAY, 0);
              put_ebml_string(dyn_cp, MATROSKA_ID_CHAPSTRING, t->value);
              put_ebml_string(dyn_cp, MATROSKA_ID_CHAPLANG  , "und");
              end_ebml_master(dyn_cp, chapterdisplay);
          }
          end_ebml_master(dyn_cp, chapteratom);
      }
      end_ebml_master(dyn_cp, editionentry);
      end_ebml_master_crc32(pb, &dyn_cp, mkv, chapters);
  
      mkv->wrote_chapters = 1;
      return 0;
  }
  
  static int mkv_write_simpletag(AVIOContext *pb, AVDictionaryEntry *t)
  {
      uint8_t *key = av_strdup(t->key);
      uint8_t *p   = key;
      const uint8_t *lang = NULL;
      ebml_master tag;
  
      if (!key)
          return AVERROR(ENOMEM);
  
      if ((p = strrchr(p, '-')) &&
          (lang = ff_convert_lang_to(p + 1, AV_LANG_ISO639_2_BIBL)))
          *p = 0;
  
      p = key;
      while (*p) {
          if (*p == ' ')
              *p = '_';
          else if (*p >= 'a' && *p <= 'z')
              *p -= 'a' - 'A';
          p++;
      }
  
      tag = start_ebml_master(pb, MATROSKA_ID_SIMPLETAG, 0);
      put_ebml_string(pb, MATROSKA_ID_TAGNAME, key);
      if (lang)
          put_ebml_string(pb, MATROSKA_ID_TAGLANG, lang);
      put_ebml_string(pb, MATROSKA_ID_TAGSTRING, t->value);
      end_ebml_master(pb, tag);
  
      av_freep(&key);
      return 0;
  }
  
  static int mkv_write_tag_targets(AVFormatContext *s,
                                   unsigned int elementid, unsigned int uid,
                                   ebml_master *tags, ebml_master* tag)
  {
      AVIOContext *pb;
      MatroskaMuxContext *mkv = s->priv_data;
      ebml_master targets;
      int ret;
  
      if (!tags->pos) {
          ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_TAGS, avio_tell(s->pb));
          if (ret < 0) return ret;
  
          start_ebml_master_crc32(s->pb, &mkv->tags_bc, mkv, tags, MATROSKA_ID_TAGS, 0);
      }
      pb = mkv->tags_bc;
  
      *tag     = start_ebml_master(pb, MATROSKA_ID_TAG,       0);
      targets = start_ebml_master(pb, MATROSKA_ID_TAGTARGETS, 0);
      if (elementid)
          put_ebml_uint(pb, elementid, uid);
      end_ebml_master(pb, targets);
      return 0;
  }
  
  static int mkv_check_tag_name(const char *name, unsigned int elementid)
  {
      return av_strcasecmp(name, "title") &&
             av_strcasecmp(name, "stereo_mode") &&
             av_strcasecmp(name, "creation_time") &&
             av_strcasecmp(name, "encoding_tool") &&
             av_strcasecmp(name, "duration") &&
             (elementid != MATROSKA_ID_TAGTARGETS_TRACKUID ||
              av_strcasecmp(name, "language")) &&
             (elementid != MATROSKA_ID_TAGTARGETS_ATTACHUID ||
              (av_strcasecmp(name, "filename") &&
               av_strcasecmp(name, "mimetype")));
  }
  
  static int mkv_write_tag(AVFormatContext *s, AVDictionary *m, unsigned int elementid,
                           unsigned int uid, ebml_master *tags)
  {
      MatroskaMuxContext *mkv = s->priv_data;
      ebml_master tag;
      int ret;
      AVDictionaryEntry *t = NULL;
  
      ret = mkv_write_tag_targets(s, elementid, uid, tags, &tag);
      if (ret < 0)
          return ret;
  
      while ((t = av_dict_get(m, "", t, AV_DICT_IGNORE_SUFFIX))) {
          if (mkv_check_tag_name(t->key, elementid)) {
              ret = mkv_write_simpletag(mkv->tags_bc, t);
              if (ret < 0)
                  return ret;
          }
      }
  
      end_ebml_master(mkv->tags_bc, tag);
      return 0;
  }
  
  static int mkv_check_tag(AVDictionary *m, unsigned int elementid)
  {
      AVDictionaryEntry *t = NULL;
  
      while ((t = av_dict_get(m, "", t, AV_DICT_IGNORE_SUFFIX)))
          if (mkv_check_tag_name(t->key, elementid))
              return 1;
  
      return 0;
  }
  
  static int mkv_write_tags(AVFormatContext *s)
  {
      MatroskaMuxContext *mkv = s->priv_data;
      int i, ret;
  
      ff_metadata_conv_ctx(s, ff_mkv_metadata_conv, NULL);
  
      if (mkv_check_tag(s->metadata, 0)) {
          ret = mkv_write_tag(s, s->metadata, 0, 0, &mkv->tags);
          if (ret < 0) return ret;
      }
  
      for (i = 0; i < s->nb_streams; i++) {
          AVStream *st = s->streams[i];
  
          if (st->codecpar->codec_type == AVMEDIA_TYPE_ATTACHMENT)
              continue;
  
          if (!mkv_check_tag(st->metadata, MATROSKA_ID_TAGTARGETS_TRACKUID))
              continue;
  
          ret = mkv_write_tag(s, st->metadata, MATROSKA_ID_TAGTARGETS_TRACKUID, i + 1, &mkv->tags);
          if (ret < 0) return ret;
      }
  
      if ((s->pb->seekable & AVIO_SEEKABLE_NORMAL) && !mkv->is_live) {
          for (i = 0; i < s->nb_streams; i++) {
              AVIOContext *pb;
              AVStream *st = s->streams[i];
              ebml_master tag_target;
              ebml_master tag;
  
              if (st->codecpar->codec_type == AVMEDIA_TYPE_ATTACHMENT)
                  continue;
  
              mkv_write_tag_targets(s, MATROSKA_ID_TAGTARGETS_TRACKUID, i + 1, &mkv->tags, &tag_target);
              pb = mkv->tags_bc;
  
              tag = start_ebml_master(pb, MATROSKA_ID_SIMPLETAG, 0);
              put_ebml_string(pb, MATROSKA_ID_TAGNAME, "DURATION");
              mkv->stream_duration_offsets[i] = avio_tell(pb);
  
              // Reserve space to write duration as a 20-byte string.
              // 2 (ebml id) + 1 (data size) + 20 (data)
              put_ebml_void(pb, 23);
              end_ebml_master(pb, tag);
              end_ebml_master(pb, tag_target);
          }
      }
  
      if (mkv->mode != MODE_WEBM) {
          for (i = 0; i < s->nb_chapters; i++) {
              AVChapter *ch = s->chapters[i];
  
              if (!mkv_check_tag(ch->metadata, MATROSKA_ID_TAGTARGETS_CHAPTERUID))
                  continue;
  
              ret = mkv_write_tag(s, ch->metadata, MATROSKA_ID_TAGTARGETS_CHAPTERUID, ch->id + mkv->chapter_id_offset, &mkv->tags);
              if (ret < 0)
                  return ret;
          }
      }
  
      if (mkv->have_attachments && mkv->mode != MODE_WEBM) {
          for (i = 0; i < mkv->attachments->num_entries; i++) {
              mkv_attachment *attachment = &mkv->attachments->entries[i];
              AVStream *st = s->streams[attachment->stream_idx];
  
              if (!mkv_check_tag(st->metadata, MATROSKA_ID_TAGTARGETS_ATTACHUID))
                  continue;
  
              ret = mkv_write_tag(s, st->metadata, MATROSKA_ID_TAGTARGETS_ATTACHUID, attachment->fileuid, &mkv->tags);
              if (ret < 0)
                  return ret;
          }
      }
  
      if (mkv->tags.pos) {
          if ((s->pb->seekable & AVIO_SEEKABLE_NORMAL) && !mkv->is_live)
              end_ebml_master_crc32_preliminary(s->pb, &mkv->tags_bc, mkv, mkv->tags);
          else
              end_ebml_master_crc32(s->pb, &mkv->tags_bc, mkv, mkv->tags);
      }
      return 0;
  }
  
  static int mkv_write_attachments(AVFormatContext *s)
  {
      MatroskaMuxContext *mkv = s->priv_data;
      AVIOContext *dyn_cp, *pb = s->pb;
      ebml_master attachments;
      AVLFG c;
      int i, ret;
  
      if (!mkv->have_attachments)
          return 0;
  
      mkv->attachments = av_mallocz(sizeof(*mkv->attachments));
      if (!mkv->attachments)
          return AVERROR(ENOMEM);
  
      av_lfg_init(&c, av_get_random_seed());
  
      ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_ATTACHMENTS, avio_tell(pb));
      if (ret < 0) return ret;
  
      ret = start_ebml_master_crc32(pb, &dyn_cp, mkv, &attachments, MATROSKA_ID_ATTACHMENTS, 0);
      if (ret < 0) return ret;
  
      for (i = 0; i < s->nb_streams; i++) {
          AVStream *st = s->streams[i];
          ebml_master attached_file;
          mkv_attachment *attachment = mkv->attachments->entries;
          AVDictionaryEntry *t;
          const char *mimetype = NULL;
          uint32_t fileuid;
  
          if (st->codecpar->codec_type != AVMEDIA_TYPE_ATTACHMENT)
              continue;
  
          attachment = av_realloc_array(attachment, mkv->attachments->num_entries + 1, sizeof(mkv_attachment));
          if (!attachment)
              return AVERROR(ENOMEM);
          mkv->attachments->entries = attachment;
  
          attached_file = start_ebml_master(dyn_cp, MATROSKA_ID_ATTACHEDFILE, 0);
  
          if (t = av_dict_get(st->metadata, "title", NULL, 0))
              put_ebml_string(dyn_cp, MATROSKA_ID_FILEDESC, t->value);
          if (!(t = av_dict_get(st->metadata, "filename", NULL, 0))) {
              av_log(s, AV_LOG_ERROR, "Attachment stream %d has no filename tag.\n", i);
              return AVERROR(EINVAL);
          }
          put_ebml_string(dyn_cp, MATROSKA_ID_FILENAME, t->value);
          if (t = av_dict_get(st->metadata, "mimetype", NULL, 0))
              mimetype = t->value;
          else if (st->codecpar->codec_id != AV_CODEC_ID_NONE ) {
              int i;
              for (i = 0; ff_mkv_mime_tags[i].id != AV_CODEC_ID_NONE; i++)
                  if (ff_mkv_mime_tags[i].id == st->codecpar->codec_id) {
                      mimetype = ff_mkv_mime_tags[i].str;
                      break;
                  }
              for (i = 0; ff_mkv_image_mime_tags[i].id != AV_CODEC_ID_NONE; i++)
                  if (ff_mkv_image_mime_tags[i].id == st->codecpar->codec_id) {
                      mimetype = ff_mkv_image_mime_tags[i].str;
                      break;
                  }
          }
          if (!mimetype) {
              av_log(s, AV_LOG_ERROR, "Attachment stream %d has no mimetype tag and "
                                      "it cannot be deduced from the codec id.\n", i);
              return AVERROR(EINVAL);
          }
  
          if (s->flags & AVFMT_FLAG_BITEXACT) {
              struct AVSHA *sha = av_sha_alloc();
              uint8_t digest[20];
              if (!sha)
                  return AVERROR(ENOMEM);
              av_sha_init(sha, 160);
              av_sha_update(sha, st->codecpar->extradata, st->codecpar->extradata_size);
              av_sha_final(sha, digest);
              av_free(sha);
              fileuid = AV_RL32(digest);
          } else {
              fileuid = av_lfg_get(&c);
          }
          av_log(s, AV_LOG_VERBOSE, "Using %.8"PRIx32" for attachment %d\n",
                 fileuid, mkv->attachments->num_entries);
  
          put_ebml_string(dyn_cp, MATROSKA_ID_FILEMIMETYPE, mimetype);
          put_ebml_binary(dyn_cp, MATROSKA_ID_FILEDATA, st->codecpar->extradata, st->codecpar->extradata_size);
          put_ebml_uint(dyn_cp, MATROSKA_ID_FILEUID, fileuid);
          end_ebml_master(dyn_cp, attached_file);
  
          mkv->attachments->entries[mkv->attachments->num_entries].stream_idx = i;
          mkv->attachments->entries[mkv->attachments->num_entries++].fileuid  = fileuid;
      }
      end_ebml_master_crc32(pb, &dyn_cp, mkv, attachments);
  
      return 0;
  }
  
  static int64_t get_metadata_duration(AVFormatContext *s)
  {
      int i = 0;
      int64_t max = 0;
      int64_t us;
  
      AVDictionaryEntry *explicitDuration = av_dict_get(s->metadata, "DURATION", NULL, 0);
      if (explicitDuration && (av_parse_time(&us, explicitDuration->value, 1) == 0) && us > 0) {
          av_log(s, AV_LOG_DEBUG, "get_metadata_duration found duration in context metadata: %" PRId64 "\n", us);
          return us;
      }
  
      for (i = 0; i < s->nb_streams; i++) {
          int64_t us;
          AVDictionaryEntry *duration = av_dict_get(s->streams[i]->metadata, "DURATION", NULL, 0);
  
          if (duration && (av_parse_time(&us, duration->value, 1) == 0))
              max = FFMAX(max, us);
      }
  
      av_log(s, AV_LOG_DEBUG, "get_metadata_duration returned: %" PRId64 "\n", max);
      return max;
  }
  
  static int mkv_write_header(AVFormatContext *s)
  {
      MatroskaMuxContext *mkv = s->priv_data;
      AVIOContext *pb = s->pb;
      ebml_master ebml_header;
      AVDictionaryEntry *tag;
      int ret, i, version = 2;
      int64_t creation_time;
  
      if (!strcmp(s->oformat->name, "webm"))
          mkv->mode = MODE_WEBM;
      else
          mkv->mode = MODE_MATROSKAv2;
  
      if (mkv->mode != MODE_WEBM ||
          av_dict_get(s->metadata, "stereo_mode", NULL, 0) ||
          av_dict_get(s->metadata, "alpha_mode", NULL, 0))
          version = 4;
  
      for (i = 0; i < s->nb_streams; i++) {
          if (s->streams[i]->codecpar->codec_id == AV_CODEC_ID_OPUS ||
              av_dict_get(s->streams[i]->metadata, "stereo_mode", NULL, 0) ||
              av_dict_get(s->streams[i]->metadata, "alpha_mode", NULL, 0))
              version = 4;
      }
  
      mkv->tracks = av_mallocz_array(s->nb_streams, sizeof(*mkv->tracks));
      if (!mkv->tracks) {
          ret = AVERROR(ENOMEM);
          goto fail;
      }
      ebml_header = start_ebml_master(pb, EBML_ID_HEADER, 0);
      put_ebml_uint   (pb, EBML_ID_EBMLVERSION        ,           1);
      put_ebml_uint   (pb, EBML_ID_EBMLREADVERSION    ,           1);
      put_ebml_uint   (pb, EBML_ID_EBMLMAXIDLENGTH    ,           4);
      put_ebml_uint   (pb, EBML_ID_EBMLMAXSIZELENGTH  ,           8);
      put_ebml_string (pb, EBML_ID_DOCTYPE            , s->oformat->name);
      put_ebml_uint   (pb, EBML_ID_DOCTYPEVERSION     ,     version);
      put_ebml_uint   (pb, EBML_ID_DOCTYPEREADVERSION ,           2);
      end_ebml_master(pb, ebml_header);
  
      mkv->segment = start_ebml_master(pb, MATROSKA_ID_SEGMENT, 0);
      mkv->segment_offset = avio_tell(pb);
  
      // we write 2 seek heads - one at the end of the file to point to each
      // cluster, and one at the beginning to point to all other level one
      // elements (including the seek head at the end of the file), which
      // isn't more than 10 elements if we only write one of each other
      // currently defined level 1 element
      mkv->main_seekhead    = mkv_start_seekhead(pb, mkv->segment_offset, 10);
      if (!mkv->main_seekhead) {
          ret = AVERROR(ENOMEM);
          goto fail;
      }
  
      ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_INFO, avio_tell(pb));
      if (ret < 0) goto fail;
  
      ret = start_ebml_master_crc32(pb, &mkv->info_bc, mkv, &mkv->info, MATROSKA_ID_INFO, 0);
      if (ret < 0)
          return ret;
      pb = mkv->info_bc;
  
      put_ebml_uint(pb, MATROSKA_ID_TIMECODESCALE, 1000000);
      if ((tag = av_dict_get(s->metadata, "title", NULL, 0)))
          put_ebml_string(pb, MATROSKA_ID_TITLE, tag->value);
      if (!(s->flags & AVFMT_FLAG_BITEXACT)) {
          put_ebml_string(pb, MATROSKA_ID_MUXINGAPP, LIBAVFORMAT_IDENT);
          if ((tag = av_dict_get(s->metadata, "encoding_tool", NULL, 0)))
              put_ebml_string(pb, MATROSKA_ID_WRITINGAPP, tag->value);
          else
              put_ebml_string(pb, MATROSKA_ID_WRITINGAPP, LIBAVFORMAT_IDENT);
  
          if (mkv->mode != MODE_WEBM) {
              uint32_t segment_uid[4];
              AVLFG lfg;
  
              av_lfg_init(&lfg, av_get_random_seed());
  
              for (i = 0; i < 4; i++)
                  segment_uid[i] = av_lfg_get(&lfg);
  
              put_ebml_binary(pb, MATROSKA_ID_SEGMENTUID, segment_uid, 16);
          }
      } else {
          const char *ident = "Lavf";
          put_ebml_string(pb, MATROSKA_ID_MUXINGAPP , ident);
          put_ebml_string(pb, MATROSKA_ID_WRITINGAPP, ident);
      }
  
      if (ff_parse_creation_time_metadata(s, &creation_time, 0) > 0) {
          // Adjust time so it's relative to 2001-01-01 and convert to nanoseconds.
          int64_t date_utc = (creation_time - 978307200000000LL) * 1000;
          uint8_t date_utc_buf[8];
          AV_WB64(date_utc_buf, date_utc);
          put_ebml_binary(pb, MATROSKA_ID_DATEUTC, date_utc_buf, 8);
      }
  
      // reserve space for the duration
      mkv->duration = 0;
      mkv->duration_offset = avio_tell(pb);
      if (!mkv->is_live) {
          int64_t metadata_duration = get_metadata_duration(s);
  
          if (s->duration > 0) {
              int64_t scaledDuration = av_rescale(s->duration, 1000, AV_TIME_BASE);
              put_ebml_float(pb, MATROSKA_ID_DURATION, scaledDuration);
              av_log(s, AV_LOG_DEBUG, "Write early duration from recording time = %" PRIu64 "\n", scaledDuration);
          } else if (metadata_duration > 0) {
              int64_t scaledDuration = av_rescale(metadata_duration, 1000, AV_TIME_BASE);
              put_ebml_float(pb, MATROSKA_ID_DURATION, scaledDuration);
              av_log(s, AV_LOG_DEBUG, "Write early duration from metadata = %" PRIu64 "\n", scaledDuration);
          } else {
              put_ebml_void(pb, 11);              // assumes double-precision float to be written
          }
      }
      if ((s->pb->seekable & AVIO_SEEKABLE_NORMAL) && !mkv->is_live)
          end_ebml_master_crc32_preliminary(s->pb, &mkv->info_bc, mkv, mkv->info);
      else
          end_ebml_master_crc32(s->pb, &mkv->info_bc, mkv, mkv->info);
      pb = s->pb;
  
      // initialize stream_duration fields
      mkv->stream_durations = av_mallocz(s->nb_streams * sizeof(int64_t));
      mkv->stream_duration_offsets = av_mallocz(s->nb_streams * sizeof(int64_t));
      if (!mkv->stream_durations || !mkv->stream_duration_offsets) {
          ret = AVERROR(ENOMEM);
          goto fail;
      }
  
      ret = mkv_write_tracks(s);
      if (ret < 0)
          goto fail;
  
      for (i = 0; i < s->nb_chapters; i++)
          mkv->chapter_id_offset = FFMAX(mkv->chapter_id_offset, 1LL - s->chapters[i]->id);
  
      ret = mkv_write_chapters(s);
      if (ret < 0)
          goto fail;
  
      if (mkv->mode != MODE_WEBM) {
          ret = mkv_write_attachments(s);
          if (ret < 0)
              goto fail;
      }
  
      ret = mkv_write_tags(s);
      if (ret < 0)
          goto fail;
  
      if (!(s->pb->seekable & AVIO_SEEKABLE_NORMAL) && !mkv->is_live)
          mkv_write_seekhead(pb, mkv);
  
      mkv->cues = mkv_start_cues(mkv->segment_offset);
      if (!mkv->cues) {
          ret = AVERROR(ENOMEM);
          goto fail;
      }
      if ((pb->seekable & AVIO_SEEKABLE_NORMAL) && mkv->reserve_cues_space) {
          mkv->cues_pos = avio_tell(pb);
          if (mkv->reserve_cues_space == 1)
              mkv->reserve_cues_space++;
          put_ebml_void(pb, mkv->reserve_cues_space);
      }
  
      av_init_packet(&mkv->cur_audio_pkt);
      mkv->cur_audio_pkt.size = 0;
      mkv->cluster_pos = -1;
  
      avio_flush(pb);
  
      // start a new cluster every 5 MB or 5 sec, or 32k / 1 sec for streaming or
      // after 4k and on a keyframe
      if (pb->seekable & AVIO_SEEKABLE_NORMAL) {
          if (mkv->cluster_time_limit < 0)
              mkv->cluster_time_limit = 5000;
          if (mkv->cluster_size_limit < 0)
              mkv->cluster_size_limit = 5 * 1024 * 1024;
      } else {
          if (mkv->cluster_time_limit < 0)
              mkv->cluster_time_limit = 1000;
          if (mkv->cluster_size_limit < 0)
              mkv->cluster_size_limit = 32 * 1024;
      }
  
      return 0;
  fail:
      mkv_free(mkv);
      return ret;
  }
  
  static int mkv_blockgroup_size(int pkt_size)
  {
      int size = pkt_size + 4;
      size += ebml_num_size(size);
      size += 2;              // EBML ID for block and block duration
      size += 8;              // max size of block duration
      size += ebml_num_size(size);
      size += 1;              // blockgroup EBML ID
      return size;
  }
  
  static int mkv_strip_wavpack(const uint8_t *src, uint8_t **pdst, int *size)
  {
      uint8_t *dst;
      int srclen = *size;
      int offset = 0;
      int ret;
  
      dst = av_malloc(srclen);
      if (!dst)
          return AVERROR(ENOMEM);
  
      while (srclen >= WV_HEADER_SIZE) {
          WvHeader header;
  
          ret = ff_wv_parse_header(&header, src);
          if (ret < 0)
              goto fail;
          src    += WV_HEADER_SIZE;
          srclen -= WV_HEADER_SIZE;
  
          if (srclen < header.blocksize) {
              ret = AVERROR_INVALIDDATA;
              goto fail;
          }
  
          if (header.initial) {
              AV_WL32(dst + offset, header.samples);
              offset += 4;
          }
          AV_WL32(dst + offset,     header.flags);
          AV_WL32(dst + offset + 4, header.crc);
          offset += 8;
  
          if (!(header.initial && header.final)) {
              AV_WL32(dst + offset, header.blocksize);
              offset += 4;
          }
  
          memcpy(dst + offset, src, header.blocksize);
          src    += header.blocksize;
          srclen -= header.blocksize;
          offset += header.blocksize;
      }
  
      *pdst = dst;
      *size = offset;
  
      return 0;
  fail:
      av_freep(&dst);
      return ret;
  }
  
  static void mkv_write_block(AVFormatContext *s, AVIOContext *pb,
                              unsigned int blockid, AVPacket *pkt, int keyframe)
  {
      MatroskaMuxContext *mkv = s->priv_data;
      AVCodecParameters *par = s->streams[pkt->stream_index]->codecpar;
      uint8_t *data = NULL, *side_data = NULL;
      int offset = 0, size = pkt->size, side_data_size = 0;
      int64_t ts = mkv->tracks[pkt->stream_index].write_dts ? pkt->dts : pkt->pts;
      uint64_t additional_id = 0;
      int64_t discard_padding = 0;
      uint8_t track_number = (mkv->is_dash ? mkv->dash_track_number : (pkt->stream_index + 1));
      ebml_master block_group, block_additions, block_more;
  
      ts += mkv->tracks[pkt->stream_index].ts_offset;
  
      av_log(s, AV_LOG_DEBUG, "Writing block at offset %" PRIu64 ", size %d, "
             "pts %" PRId64 ", dts %" PRId64 ", duration %" PRId64 ", keyframe %d\n",
             avio_tell(pb), pkt->size, pkt->pts, pkt->dts, pkt->duration,
             keyframe != 0);
      if (par->codec_id == AV_CODEC_ID_H264 && par->extradata_size > 0 &&
          (AV_RB24(par->extradata) == 1 || AV_RB32(par->extradata) == 1))
          ff_avc_parse_nal_units_buf(pkt->data, &data, &size);
      else if (par->codec_id == AV_CODEC_ID_HEVC && par->extradata_size > 6 &&
               (AV_RB24(par->extradata) == 1 || AV_RB32(par->extradata) == 1))
          /* extradata is Annex B, assume the bitstream is too and convert it */
          ff_hevc_annexb2mp4_buf(pkt->data, &data, &size, 0, NULL);
      else if (par->codec_id == AV_CODEC_ID_WAVPACK) {
          int ret = mkv_strip_wavpack(pkt->data, &data, &size);
          if (ret < 0) {
              av_log(s, AV_LOG_ERROR, "Error stripping a WavPack packet.\n");
              return;
          }
      } else
          data = pkt->data;
  
      if (par->codec_id == AV_CODEC_ID_PRORES && size >= 8) {
          /* Matroska specification requires to remove the first QuickTime atom
           */
          size  -= 8;
          offset = 8;
      }
  
      side_data = av_packet_get_side_data(pkt,
                                          AV_PKT_DATA_SKIP_SAMPLES,
                                          &side_data_size);
  
      if (side_data && side_data_size >= 10) {
          discard_padding = av_rescale_q(AV_RL32(side_data + 4),
                                         (AVRational){1, par->sample_rate},
                                         (AVRational){1, 1000000000});
      }
  
      side_data = av_packet_get_side_data(pkt,
                                          AV_PKT_DATA_MATROSKA_BLOCKADDITIONAL,
                                          &side_data_size);
      if (side_data) {
          additional_id = AV_RB64(side_data);
          side_data += 8;
          side_data_size -= 8;
      }
  
      if ((side_data_size && additional_id == 1) || discard_padding) {
          block_group = start_ebml_master(pb, MATROSKA_ID_BLOCKGROUP, 0);
          blockid = MATROSKA_ID_BLOCK;
      }
  
      put_ebml_id(pb, blockid);
      put_ebml_num(pb, size + 4, 0);
      // this assumes stream_index is less than 126
      avio_w8(pb, 0x80 | track_number);
      avio_wb16(pb, ts - mkv->cluster_pts);
      avio_w8(pb, (blockid == MATROSKA_ID_SIMPLEBLOCK && keyframe) ? (1 << 7) : 0);
      avio_write(pb, data + offset, size);
      if (data != pkt->data)
          av_free(data);
  
      if (blockid == MATROSKA_ID_BLOCK && !keyframe) {
          put_ebml_sint(pb, MATROSKA_ID_BLOCKREFERENCE,
                        mkv->last_track_timestamp[track_number - 1]);
      }
      mkv->last_track_timestamp[track_number - 1] = ts - mkv->cluster_pts;
  
      if (discard_padding) {
          put_ebml_sint(pb, MATROSKA_ID_DISCARDPADDING, discard_padding);
      }
  
      if (side_data_size && additional_id == 1) {
          block_additions = start_ebml_master(pb, MATROSKA_ID_BLOCKADDITIONS, 0);
          block_more = start_ebml_master(pb, MATROSKA_ID_BLOCKMORE, 0);
          put_ebml_uint(pb, MATROSKA_ID_BLOCKADDID, 1);
          put_ebml_id(pb, MATROSKA_ID_BLOCKADDITIONAL);
          put_ebml_num(pb, side_data_size, 0);
          avio_write(pb, side_data, side_data_size);
          end_ebml_master(pb, block_more);
          end_ebml_master(pb, block_additions);
      }
      if ((side_data_size && additional_id == 1) || discard_padding) {
          end_ebml_master(pb, block_group);
      }
  }
  
  static int mkv_write_vtt_blocks(AVFormatContext *s, AVIOContext *pb, AVPacket *pkt)
  {
      MatroskaMuxContext *mkv = s->priv_data;
      ebml_master blockgroup;
      int id_size, settings_size, size;
      uint8_t *id, *settings;
      int64_t ts = mkv->tracks[pkt->stream_index].write_dts ? pkt->dts : pkt->pts;
      const int flags = 0;
  
      id_size = 0;
      id = av_packet_get_side_data(pkt, AV_PKT_DATA_WEBVTT_IDENTIFIER,
                                   &id_size);
  
      settings_size = 0;
      settings = av_packet_get_side_data(pkt, AV_PKT_DATA_WEBVTT_SETTINGS,
                                         &settings_size);
  
      size = id_size + 1 + settings_size + 1 + pkt->size;
  
      av_log(s, AV_LOG_DEBUG, "Writing block at offset %" PRIu64 ", size %d, "
             "pts %" PRId64 ", dts %" PRId64 ", duration %" PRId64 ", flags %d\n",
             avio_tell(pb), size, pkt->pts, pkt->dts, pkt->duration, flags);
  
      blockgroup = start_ebml_master(pb, MATROSKA_ID_BLOCKGROUP, mkv_blockgroup_size(size));
  
      put_ebml_id(pb, MATROSKA_ID_BLOCK);
      put_ebml_num(pb, size + 4, 0);
      avio_w8(pb, 0x80 | (pkt->stream_index + 1));     // this assumes stream_index is less than 126
      avio_wb16(pb, ts - mkv->cluster_pts);
      avio_w8(pb, flags);
      avio_printf(pb, "%.*s\n%.*s\n%.*s", id_size, id, settings_size, settings, pkt->size, pkt->data);
  
      put_ebml_uint(pb, MATROSKA_ID_BLOCKDURATION, pkt->duration);
      end_ebml_master(pb, blockgroup);
  
      return pkt->duration;
  }
  
  static void mkv_start_new_cluster(AVFormatContext *s, AVPacket *pkt)
  {
      MatroskaMuxContext *mkv = s->priv_data;
  
      end_ebml_master_crc32(s->pb, &mkv->dyn_bc, mkv, mkv->cluster);
      mkv->cluster_pos = -1;
      if (s->pb->seekable & AVIO_SEEKABLE_NORMAL)
          av_log(s, AV_LOG_DEBUG,
                 "Starting new cluster at offset %" PRIu64 " bytes, "
                 "pts %" PRIu64 "dts %" PRIu64 "\n",
                 avio_tell(s->pb), pkt->pts, pkt->dts);
      else
          av_log(s, AV_LOG_DEBUG, "Starting new cluster, "
                 "pts %" PRIu64 "dts %" PRIu64 "\n",
                 pkt->pts, pkt->dts);
      avio_flush(s->pb);
  }
  
  static int mkv_check_new_extra_data(AVFormatContext *s, AVPacket *pkt)
  {
      MatroskaMuxContext *mkv = s->priv_data;
      mkv_track *track        = &mkv->tracks[pkt->stream_index];
      AVCodecParameters *par  = s->streams[pkt->stream_index]->codecpar;
      uint8_t *side_data;
      int side_data_size = 0, ret;
  
      side_data = av_packet_get_side_data(pkt, AV_PKT_DATA_NEW_EXTRADATA,
                                          &side_data_size);
  
      switch (par->codec_id) {
      case AV_CODEC_ID_AAC:
          if (side_data_size && (s->pb->seekable & AVIO_SEEKABLE_NORMAL) && !mkv->is_live) {
              int filler, output_sample_rate = 0;
              int64_t curpos;
              ret = get_aac_sample_rates(s, side_data, side_data_size, &track->sample_rate,
                                         &output_sample_rate);
              if (ret < 0)
                  return ret;
              if (!output_sample_rate)
                  output_sample_rate = track->sample_rate; // Space is already reserved, so it's this or a void element.
              av_freep(&par->extradata);
              ret = ff_alloc_extradata(par, side_data_size);
              if (ret < 0)
                  return ret;
              memcpy(par->extradata, side_data, side_data_size);
              curpos = avio_tell(mkv->tracks_bc);
              avio_seek(mkv->tracks_bc, track->codecpriv_offset, SEEK_SET);
              mkv_write_codecprivate(s, mkv->tracks_bc, par, 1, 0);
              filler = MAX_PCE_SIZE + 2 + 4 - (avio_tell(mkv->tracks_bc) - track->codecpriv_offset);
              if (filler)
                  put_ebml_void(mkv->tracks_bc, filler);
              avio_seek(mkv->tracks_bc, track->sample_rate_offset, SEEK_SET);
              put_ebml_float(mkv->tracks_bc, MATROSKA_ID_AUDIOSAMPLINGFREQ, track->sample_rate);
              put_ebml_float(mkv->tracks_bc, MATROSKA_ID_AUDIOOUTSAMPLINGFREQ, output_sample_rate);
              avio_seek(mkv->tracks_bc, curpos, SEEK_SET);
          } else if (!par->extradata_size && !track->sample_rate) {
              // No extradata (codecpar or packet side data).
              av_log(s, AV_LOG_ERROR, "Error parsing AAC extradata, unable to determine samplerate.\n");
              return AVERROR(EINVAL);
          }
          break;
      case AV_CODEC_ID_FLAC:
          if (side_data_size && (s->pb->seekable & AVIO_SEEKABLE_NORMAL) && !mkv->is_live) {
              AVCodecParameters *codecpriv_par;
              int64_t curpos;
              if (side_data_size != par->extradata_size) {
                  av_log(s, AV_LOG_ERROR, "Invalid FLAC STREAMINFO metadata for output stream %d\n",
                         pkt->stream_index);
                  return AVERROR(EINVAL);
              }
              codecpriv_par = avcodec_parameters_alloc();
              if (!codecpriv_par)
                  return AVERROR(ENOMEM);
              ret = avcodec_parameters_copy(codecpriv_par, par);
              if (ret < 0) {
                  avcodec_parameters_free(&codecpriv_par);
                  return ret;
              }
              memcpy(codecpriv_par->extradata, side_data, side_data_size);
              curpos = avio_tell(mkv->tracks_bc);
              avio_seek(mkv->tracks_bc, track->codecpriv_offset, SEEK_SET);
              mkv_write_codecprivate(s, mkv->tracks_bc, codecpriv_par, 1, 0);
              avio_seek(mkv->tracks_bc, curpos, SEEK_SET);
              avcodec_parameters_free(&codecpriv_par);
          }
          break;
      default:
          if (side_data_size)
              av_log(s, AV_LOG_DEBUG, "Ignoring new extradata in a packet for stream %d.\n", pkt->stream_index);
          break;
      }
  
      return 0;
  }
  
  static int mkv_write_packet_internal(AVFormatContext *s, AVPacket *pkt, int add_cue)
  {
      MatroskaMuxContext *mkv = s->priv_data;
      AVIOContext *pb         = s->pb;
      AVCodecParameters *par  = s->streams[pkt->stream_index]->codecpar;
      int keyframe            = !!(pkt->flags & AV_PKT_FLAG_KEY);
      int duration            = pkt->duration;
      int ret;
      int64_t ts = mkv->tracks[pkt->stream_index].write_dts ? pkt->dts : pkt->pts;
      int64_t relative_packet_pos;
      int dash_tracknum = mkv->is_dash ? mkv->dash_track_number : pkt->stream_index + 1;
  
      if (ts == AV_NOPTS_VALUE) {
          av_log(s, AV_LOG_ERROR, "Can't write packet with unknown timestamp\n");
          return AVERROR(EINVAL);
      }
      ts += mkv->tracks[pkt->stream_index].ts_offset;
  
      if (mkv->cluster_pos != -1) {
          int64_t cluster_time = ts - mkv->cluster_pts + mkv->tracks[pkt->stream_index].ts_offset;
          if ((int16_t)cluster_time != cluster_time) {
              av_log(s, AV_LOG_WARNING, "Starting new cluster due to timestamp\n");
              mkv_start_new_cluster(s, pkt);
          }
      }
  
      if (mkv->cluster_pos == -1) {
          mkv->cluster_pos = avio_tell(s->pb);
          ret = start_ebml_master_crc32(s->pb, &mkv->dyn_bc, mkv, &mkv->cluster, MATROSKA_ID_CLUSTER, 0);
          if (ret < 0)
              return ret;
          put_ebml_uint(mkv->dyn_bc, MATROSKA_ID_CLUSTERTIMECODE, FFMAX(0, ts));
          mkv->cluster_pts = FFMAX(0, ts);
      }
      pb = mkv->dyn_bc;
  
      relative_packet_pos = avio_tell(pb);
  
      if (par->codec_type != AVMEDIA_TYPE_SUBTITLE) {
          mkv_write_block(s, pb, MATROSKA_ID_SIMPLEBLOCK, pkt, keyframe);
          if ((s->pb->seekable & AVIO_SEEKABLE_NORMAL) && (par->codec_type == AVMEDIA_TYPE_VIDEO && keyframe || add_cue)) {
              ret = mkv_add_cuepoint(mkv->cues, pkt->stream_index, dash_tracknum, ts, mkv->cluster_pos, relative_packet_pos, -1);
              if (ret < 0) return ret;
          }
      } else {
          if (par->codec_id == AV_CODEC_ID_WEBVTT) {
              duration = mkv_write_vtt_blocks(s, pb, pkt);
          } else {
              ebml_master blockgroup = start_ebml_master(pb, MATROSKA_ID_BLOCKGROUP,
                                                         mkv_blockgroup_size(pkt->size));
  
  #if FF_API_CONVERGENCE_DURATION
  FF_DISABLE_DEPRECATION_WARNINGS
              /* For backward compatibility, prefer convergence_duration. */
              if (pkt->convergence_duration > 0) {
                  duration = pkt->convergence_duration;
              }
  FF_ENABLE_DEPRECATION_WARNINGS
  #endif
              /* All subtitle blocks are considered to be keyframes. */
              mkv_write_block(s, pb, MATROSKA_ID_BLOCK, pkt, 1);
              put_ebml_uint(pb, MATROSKA_ID_BLOCKDURATION, duration);
              end_ebml_master(pb, blockgroup);
          }
  
          if (s->pb->seekable & AVIO_SEEKABLE_NORMAL) {
              ret = mkv_add_cuepoint(mkv->cues, pkt->stream_index, dash_tracknum, ts,
                                     mkv->cluster_pos, relative_packet_pos, duration);
              if (ret < 0)
                  return ret;
          }
      }
  
      mkv->duration = FFMAX(mkv->duration, ts + duration);
  
      if (mkv->stream_durations)
          mkv->stream_durations[pkt->stream_index] =
              FFMAX(mkv->stream_durations[pkt->stream_index], ts + duration);
  
      return 0;
  }
  
  static int mkv_write_packet(AVFormatContext *s, AVPacket *pkt)
  {
      MatroskaMuxContext *mkv = s->priv_data;
      int codec_type          = s->streams[pkt->stream_index]->codecpar->codec_type;
      int keyframe            = !!(pkt->flags & AV_PKT_FLAG_KEY);
      int cluster_size;
      int64_t cluster_time;
      int ret;
      int start_new_cluster;
  
      ret = mkv_check_new_extra_data(s, pkt);
      if (ret < 0)
          return ret;
  
      if (mkv->tracks[pkt->stream_index].write_dts)
          cluster_time = pkt->dts - mkv->cluster_pts;
      else
          cluster_time = pkt->pts - mkv->cluster_pts;
      cluster_time += mkv->tracks[pkt->stream_index].ts_offset;
  
      // start a new cluster every 5 MB or 5 sec, or 32k / 1 sec for streaming or
      // after 4k and on a keyframe
      cluster_size = avio_tell(mkv->dyn_bc);
  
      if (mkv->is_dash && codec_type == AVMEDIA_TYPE_VIDEO) {
          // WebM DASH specification states that the first block of every cluster
          // has to be a key frame. So for DASH video, we only create a cluster
          // on seeing key frames.
          start_new_cluster = keyframe;
      } else if (mkv->is_dash && codec_type == AVMEDIA_TYPE_AUDIO &&
                 (mkv->cluster_pos == -1 ||
                  cluster_time > mkv->cluster_time_limit)) {
          // For DASH audio, we create a Cluster based on cluster_time_limit
          start_new_cluster = 1;
      } else if (!mkv->is_dash &&
                 (cluster_size > mkv->cluster_size_limit ||
                  cluster_time > mkv->cluster_time_limit ||
                  (codec_type == AVMEDIA_TYPE_VIDEO && keyframe &&
                   cluster_size > 4 * 1024))) {
          start_new_cluster = 1;
      } else {
          start_new_cluster = 0;
      }
  
      if (mkv->cluster_pos != -1 && start_new_cluster) {
          mkv_start_new_cluster(s, pkt);
      }
  
      if (!mkv->cluster_pos)
          avio_write_marker(s->pb,
                            av_rescale_q(pkt->dts, s->streams[pkt->stream_index]->time_base, AV_TIME_BASE_Q),
                            keyframe && (mkv->have_video ? codec_type == AVMEDIA_TYPE_VIDEO : 1) ? AVIO_DATA_MARKER_SYNC_POINT : AVIO_DATA_MARKER_BOUNDARY_POINT);
  
      // check if we have an audio packet cached
      if (mkv->cur_audio_pkt.size > 0) {
          // for DASH audio, a CuePoint has to be added when there is a new cluster.
          ret = mkv_write_packet_internal(s, &mkv->cur_audio_pkt,
                                          mkv->is_dash ? start_new_cluster : 0);
          av_packet_unref(&mkv->cur_audio_pkt);
          if (ret < 0) {
              av_log(s, AV_LOG_ERROR,
                     "Could not write cached audio packet ret:%d\n", ret);
              return ret;
          }
      }
  
      // buffer an audio packet to ensure the packet containing the video
      // keyframe's timecode is contained in the same cluster for WebM
      if (codec_type == AVMEDIA_TYPE_AUDIO) {
          ret = av_packet_ref(&mkv->cur_audio_pkt, pkt);
      } else
          ret = mkv_write_packet_internal(s, pkt, 0);
      return ret;
  }
  
  static int mkv_write_flush_packet(AVFormatContext *s, AVPacket *pkt)
  {
      MatroskaMuxContext *mkv = s->priv_data;
  
      if (!pkt) {
          if (mkv->cluster_pos != -1) {
              end_ebml_master_crc32(s->pb, &mkv->dyn_bc, mkv, mkv->cluster);
              mkv->cluster_pos = -1;
              if (s->pb->seekable & AVIO_SEEKABLE_NORMAL)
                  av_log(s, AV_LOG_DEBUG,
                         "Flushing cluster at offset %" PRIu64 " bytes\n",
                         avio_tell(s->pb));
              else
                  av_log(s, AV_LOG_DEBUG, "Flushing cluster\n");
              avio_flush(s->pb);
          }
          return 1;
      }
      return mkv_write_packet(s, pkt);
  }
  
  static int mkv_write_trailer(AVFormatContext *s)
  {
      MatroskaMuxContext *mkv = s->priv_data;
      AVIOContext *pb = s->pb;
      int64_t currentpos, cuespos;
      int ret;
  
      // check if we have an audio packet cached
      if (mkv->cur_audio_pkt.size > 0) {
          ret = mkv_write_packet_internal(s, &mkv->cur_audio_pkt, 0);
          av_packet_unref(&mkv->cur_audio_pkt);
          if (ret < 0) {
              av_log(s, AV_LOG_ERROR,
                     "Could not write cached audio packet ret:%d\n", ret);
              return ret;
          }
      }
  
      if (mkv->dyn_bc) {
          end_ebml_master_crc32(pb, &mkv->dyn_bc, mkv, mkv->cluster);
      }
  
      ret = mkv_write_chapters(s);
      if (ret < 0)
          return ret;
  
  
      if ((pb->seekable & AVIO_SEEKABLE_NORMAL) && !mkv->is_live) {
          if (mkv->cues->num_entries) {
              if (mkv->reserve_cues_space) {
                  int64_t cues_end;
  
                  currentpos = avio_tell(pb);
                  avio_seek(pb, mkv->cues_pos, SEEK_SET);
  
                  cuespos  = mkv_write_cues(s, mkv->cues, mkv->tracks, s->nb_streams);
                  cues_end = avio_tell(pb);
                  if (cues_end > cuespos + mkv->reserve_cues_space) {
                      av_log(s, AV_LOG_ERROR,
                             "Insufficient space reserved for cues: %d "
                             "(needed: %" PRId64 ").\n",
                             mkv->reserve_cues_space, cues_end - cuespos);
                      return AVERROR(EINVAL);
                  }
  
                  if (cues_end < cuespos + mkv->reserve_cues_space)
                      put_ebml_void(pb, mkv->reserve_cues_space -
                                    (cues_end - cuespos));
  
                  avio_seek(pb, currentpos, SEEK_SET);
              } else {
                  cuespos = mkv_write_cues(s, mkv->cues, mkv->tracks, s->nb_streams);
              }
  
              ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_CUES,
                                           cuespos);
              if (ret < 0)
                  return ret;
          }
  
          mkv_write_seekhead(pb, mkv);
  
          // update the duration
          av_log(s, AV_LOG_DEBUG, "end duration = %" PRIu64 "\n", mkv->duration);
          currentpos = avio_tell(pb);
          avio_seek(mkv->info_bc, mkv->duration_offset, SEEK_SET);
          put_ebml_float(mkv->info_bc, MATROSKA_ID_DURATION, mkv->duration);
          avio_seek(pb, mkv->info.pos, SEEK_SET);
          end_ebml_master_crc32(pb, &mkv->info_bc, mkv, mkv->info);
  
          // write tracks master
          avio_seek(pb, mkv->tracks_master.pos, SEEK_SET);
          end_ebml_master_crc32(pb, &mkv->tracks_bc, mkv, mkv->tracks_master);
  
          // update stream durations
          if (!mkv->is_live && mkv->stream_durations) {
              int i;
              int64_t curr = avio_tell(mkv->tags_bc);
              for (i = 0; i < s->nb_streams; ++i) {
                  AVStream *st = s->streams[i];
  
                  if (mkv->stream_duration_offsets[i] > 0) {
                      double duration_sec = mkv->stream_durations[i] * av_q2d(st->time_base);
                      char duration_string[20] = "";
  
                      av_log(s, AV_LOG_DEBUG, "stream %d end duration = %" PRIu64 "\n", i,
                             mkv->stream_durations[i]);
  
                      avio_seek(mkv->tags_bc, mkv->stream_duration_offsets[i], SEEK_SET);
  
                      snprintf(duration_string, 20, "%02d:%02d:%012.9f",
                               (int) duration_sec / 3600, ((int) duration_sec / 60) % 60,
                               fmod(duration_sec, 60));
  
                      put_ebml_binary(mkv->tags_bc, MATROSKA_ID_TAGSTRING, duration_string, 20);
                  }
              }
              avio_seek(mkv->tags_bc, curr, SEEK_SET);
          }
          if (mkv->tags.pos && !mkv->is_live) {
              avio_seek(pb, mkv->tags.pos, SEEK_SET);
              end_ebml_master_crc32(pb, &mkv->tags_bc, mkv, mkv->tags);
          }
  
          avio_seek(pb, currentpos, SEEK_SET);
      }
  
      if (!mkv->is_live) {
          end_ebml_master(pb, mkv->segment);
      }
  
      mkv_free(mkv);
      return 0;
  }
  
  static int mkv_query_codec(enum AVCodecID codec_id, int std_compliance)
  {
      int i;
      for (i = 0; ff_mkv_codec_tags[i].id != AV_CODEC_ID_NONE; i++)
          if (ff_mkv_codec_tags[i].id == codec_id)
              return 1;
  
      if (std_compliance < FF_COMPLIANCE_NORMAL) {
          enum AVMediaType type = avcodec_get_type(codec_id);
          // mkv theoretically supports any video/audio through VFW/ACM
          if (type == AVMEDIA_TYPE_VIDEO || type == AVMEDIA_TYPE_AUDIO)
              return 1;
      }
  
      return 0;
  }
  
  static int mkv_init(struct AVFormatContext *s)
  {
      int i;
  
      if (s->nb_streams > MAX_TRACKS) {
          av_log(s, AV_LOG_ERROR,
                 "At most %d streams are supported for muxing in Matroska\n",
                 MAX_TRACKS);
          return AVERROR(EINVAL);
      }
  
      for (i = 0; i < s->nb_streams; i++) {
          if (s->streams[i]->codecpar->codec_id == AV_CODEC_ID_ATRAC3 ||
              s->streams[i]->codecpar->codec_id == AV_CODEC_ID_COOK ||
              s->streams[i]->codecpar->codec_id == AV_CODEC_ID_RA_288 ||
              s->streams[i]->codecpar->codec_id == AV_CODEC_ID_SIPR ||
              s->streams[i]->codecpar->codec_id == AV_CODEC_ID_RV10 ||
              s->streams[i]->codecpar->codec_id == AV_CODEC_ID_RV20) {
              av_log(s, AV_LOG_ERROR,
                     "The Matroska muxer does not yet support muxing %s\n",
                     avcodec_get_name(s->streams[i]->codecpar->codec_id));
              return AVERROR_PATCHWELCOME;
          }
      }
  
      if (s->avoid_negative_ts < 0) {
          s->avoid_negative_ts = 1;
          s->internal->avoid_negative_ts_use_pts = 1;
      }
  
      for (i = 0; i < s->nb_streams; i++) {
          // ms precision is the de-facto standard timescale for mkv files
          avpriv_set_pts_info(s->streams[i], 64, 1, 1000);
      }
  
      return 0;
  }
  
  static int mkv_check_bitstream(struct AVFormatContext *s, const AVPacket *pkt)
  {
      int ret = 1;
      AVStream *st = s->streams[pkt->stream_index];
  
      if (st->codecpar->codec_id == AV_CODEC_ID_AAC) {
          if (pkt->size > 2 && (AV_RB16(pkt->data) & 0xfff0) == 0xfff0)
              ret = ff_stream_add_bitstream_filter(st, "aac_adtstoasc", NULL);
      } else if (st->codecpar->codec_id == AV_CODEC_ID_VP9) {
          ret = ff_stream_add_bitstream_filter(st, "vp9_superframe", NULL);
      }
  
      return ret;
  }
  
  static const AVCodecTag additional_audio_tags[] = {
      { AV_CODEC_ID_ALAC,      0XFFFFFFFF },
      { AV_CODEC_ID_EAC3,      0XFFFFFFFF },
      { AV_CODEC_ID_MLP,       0xFFFFFFFF },
      { AV_CODEC_ID_OPUS,      0xFFFFFFFF },
      { AV_CODEC_ID_PCM_S16BE, 0xFFFFFFFF },
      { AV_CODEC_ID_PCM_S24BE, 0xFFFFFFFF },
      { AV_CODEC_ID_PCM_S32BE, 0xFFFFFFFF },
      { AV_CODEC_ID_QDMC,      0xFFFFFFFF },
      { AV_CODEC_ID_QDM2,      0xFFFFFFFF },
      { AV_CODEC_ID_RA_144,    0xFFFFFFFF },
      { AV_CODEC_ID_RA_288,    0xFFFFFFFF },
      { AV_CODEC_ID_COOK,      0xFFFFFFFF },
      { AV_CODEC_ID_TRUEHD,    0xFFFFFFFF },
      { AV_CODEC_ID_NONE,      0xFFFFFFFF }
  };
  
  static const AVCodecTag additional_video_tags[] = {
      { AV_CODEC_ID_RV10,      0xFFFFFFFF },
      { AV_CODEC_ID_RV20,      0xFFFFFFFF },
      { AV_CODEC_ID_RV30,      0xFFFFFFFF },
      { AV_CODEC_ID_RV40,      0xFFFFFFFF },
      { AV_CODEC_ID_VP9,       0xFFFFFFFF },
      { AV_CODEC_ID_NONE,      0xFFFFFFFF }
  };
  
  static const AVCodecTag additional_subtitle_tags[] = {
      { AV_CODEC_ID_DVB_SUBTITLE,      0xFFFFFFFF },
      { AV_CODEC_ID_HDMV_PGS_SUBTITLE, 0xFFFFFFFF },
      { AV_CODEC_ID_NONE,              0xFFFFFFFF }
  };
  
  #define OFFSET(x) offsetof(MatroskaMuxContext, x)
  #define FLAGS AV_OPT_FLAG_ENCODING_PARAM
  static const AVOption options[] = {
      { "reserve_index_space", "Reserve a given amount of space (in bytes) at the beginning of the file for the index (cues).", OFFSET(reserve_cues_space), AV_OPT_TYPE_INT,   { .i64 = 0 },   0, INT_MAX,   FLAGS },
      { "cluster_size_limit",  "Store at most the provided amount of bytes in a cluster. ",                                     OFFSET(cluster_size_limit), AV_OPT_TYPE_INT  , { .i64 = -1 }, -1, INT_MAX,   FLAGS },
      { "cluster_time_limit",  "Store at most the provided number of milliseconds in a cluster.",                               OFFSET(cluster_time_limit), AV_OPT_TYPE_INT64, { .i64 = -1 }, -1, INT64_MAX, FLAGS },
      { "dash", "Create a WebM file conforming to WebM DASH specification", OFFSET(is_dash), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, FLAGS },
      { "dash_track_number", "Track number for the DASH stream", OFFSET(dash_track_number), AV_OPT_TYPE_INT, { .i64 = 1 }, 0, 127, FLAGS },
      { "live", "Write files assuming it is a live stream.", OFFSET(is_live), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, FLAGS },
      { "allow_raw_vfw", "allow RAW VFW mode", OFFSET(allow_raw_vfw), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, FLAGS },
      { "write_crc32", "write a CRC32 element inside every Level 1 element", OFFSET(write_crc), AV_OPT_TYPE_BOOL, { .i64 = 1 }, 0, 1, FLAGS },
      { NULL },
  };
  
  #if CONFIG_MATROSKA_MUXER
  static const AVClass matroska_class = {
      .class_name = "matroska muxer",
      .item_name  = av_default_item_name,
      .option     = options,
      .version    = LIBAVUTIL_VERSION_INT,
  };
  
  AVOutputFormat ff_matroska_muxer = {
      .name              = "matroska",
      .long_name         = NULL_IF_CONFIG_SMALL("Matroska"),
      .mime_type         = "video/x-matroska",
      .extensions        = "mkv",
      .priv_data_size    = sizeof(MatroskaMuxContext),
      .audio_codec       = CONFIG_LIBVORBIS_ENCODER ?
                           AV_CODEC_ID_VORBIS : AV_CODEC_ID_AC3,
      .video_codec       = CONFIG_LIBX264_ENCODER ?
                           AV_CODEC_ID_H264 : AV_CODEC_ID_MPEG4,
      .init              = mkv_init,
      .write_header      = mkv_write_header,
      .write_packet      = mkv_write_flush_packet,
      .write_trailer     = mkv_write_trailer,
      .flags             = AVFMT_GLOBALHEADER | AVFMT_VARIABLE_FPS |
                           AVFMT_TS_NONSTRICT | AVFMT_ALLOW_FLUSH,
      .codec_tag         = (const AVCodecTag* const []){
           ff_codec_bmp_tags, ff_codec_wav_tags,
           additional_audio_tags, additional_video_tags, additional_subtitle_tags, 0
      },
      .subtitle_codec    = AV_CODEC_ID_ASS,
      .query_codec       = mkv_query_codec,
      .check_bitstream   = mkv_check_bitstream,
      .priv_class        = &matroska_class,
  };
  #endif
  
  #if CONFIG_WEBM_MUXER
  static const AVClass webm_class = {
      .class_name = "webm muxer",
      .item_name  = av_default_item_name,
      .option     = options,
      .version    = LIBAVUTIL_VERSION_INT,
  };
  
  AVOutputFormat ff_webm_muxer = {
      .name              = "webm",
      .long_name         = NULL_IF_CONFIG_SMALL("WebM"),
      .mime_type         = "video/webm",
      .extensions        = "webm",
      .priv_data_size    = sizeof(MatroskaMuxContext),
      .audio_codec       = CONFIG_LIBOPUS_ENCODER ? AV_CODEC_ID_OPUS : AV_CODEC_ID_VORBIS,
      .video_codec       = CONFIG_LIBVPX_VP9_ENCODER? AV_CODEC_ID_VP9 : AV_CODEC_ID_VP8,
      .subtitle_codec    = AV_CODEC_ID_WEBVTT,
      .init              = mkv_init,
      .write_header      = mkv_write_header,
      .write_packet      = mkv_write_flush_packet,
      .write_trailer     = mkv_write_trailer,
      .check_bitstream   = mkv_check_bitstream,
      .flags             = AVFMT_GLOBALHEADER | AVFMT_VARIABLE_FPS |
                           AVFMT_TS_NONSTRICT | AVFMT_ALLOW_FLUSH,
      .priv_class        = &webm_class,
  };
  #endif
  
  #if CONFIG_MATROSKA_AUDIO_MUXER
  static const AVClass mka_class = {
      .class_name = "matroska audio muxer",
      .item_name  = av_default_item_name,
      .option     = options,
      .version    = LIBAVUTIL_VERSION_INT,
  };
  AVOutputFormat ff_matroska_audio_muxer = {
      .name              = "matroska",
      .long_name         = NULL_IF_CONFIG_SMALL("Matroska Audio"),
      .mime_type         = "audio/x-matroska",
      .extensions        = "mka",
      .priv_data_size    = sizeof(MatroskaMuxContext),
      .audio_codec       = CONFIG_LIBVORBIS_ENCODER ?
                           AV_CODEC_ID_VORBIS : AV_CODEC_ID_AC3,
      .video_codec       = AV_CODEC_ID_NONE,
      .init              = mkv_init,
      .write_header      = mkv_write_header,
      .write_packet      = mkv_write_flush_packet,
      .write_trailer     = mkv_write_trailer,
      .check_bitstream   = mkv_check_bitstream,
      .flags             = AVFMT_GLOBALHEADER | AVFMT_TS_NONSTRICT |
                           AVFMT_ALLOW_FLUSH,
      .codec_tag         = (const AVCodecTag* const []){
          ff_codec_wav_tags, additional_audio_tags, 0
      },
      .priv_class        = &mka_class,
  };
  #endif
  