text: /*
   * Matroska file demuxer
   * Copyright (c) 2003-2008 The FFmpeg Project
   *
   * 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
   */
  
  /**
   * @file
   * Matroska file demuxer
   * @author Ronald Bultje <rbultje@ronald.bitfreak.net>
   * @author with a little help from Moritz Bunkus <moritz@bunkus.org>
   * @author totally reworked by Aurelien Jacobs <aurel@gnuage.org>
   * @see specs available on the Matroska project page: http://www.matroska.org/
   */
  
  #include <stdio.h>
  #include "avformat.h"
  #include "internal.h"
  #include "avio_internal.h"
  /* For ff_codec_get_id(). */
  #include "riff.h"
  #include "isom.h"
  #include "rm.h"
  #include "matroska.h"
  #include "libavcodec/mpeg4audio.h"
  #include "libavutil/intfloat.h"
  #include "libavutil/intreadwrite.h"
  #include "libavutil/avstring.h"
  #include "libavutil/lzo.h"
  #include "libavutil/dict.h"
  #if CONFIG_ZLIB
  #include <zlib.h>
  #endif
  #if CONFIG_BZLIB
  #include <bzlib.h>
  #endif
  
  typedef enum {
      EBML_NONE,
      EBML_UINT,
      EBML_FLOAT,
      EBML_STR,
      EBML_UTF8,
      EBML_BIN,
      EBML_NEST,
      EBML_PASS,
      EBML_STOP,
      EBML_TYPE_COUNT
  } EbmlType;
  
  typedef const struct EbmlSyntax {
      uint32_t id;
      EbmlType type;
      int list_elem_size;
      int data_offset;
      union {
          uint64_t    u;
          double      f;
          const char *s;
          const struct EbmlSyntax *n;
      } def;
  } EbmlSyntax;
  
  typedef struct {
      int nb_elem;
      void *elem;
  } EbmlList;
  
  typedef struct {
      int      size;
      uint8_t *data;
      int64_t  pos;
  } EbmlBin;
  
  typedef struct {
      uint64_t version;
      uint64_t max_size;
      uint64_t id_length;
      char    *doctype;
      uint64_t doctype_version;
  } Ebml;
  
  typedef struct {
      uint64_t algo;
      EbmlBin  settings;
  } MatroskaTrackCompression;
  
  typedef struct {
      uint64_t scope;
      uint64_t type;
      MatroskaTrackCompression compression;
  } MatroskaTrackEncoding;
  
  typedef struct {
      double   frame_rate;
      uint64_t display_width;
      uint64_t display_height;
      uint64_t pixel_width;
      uint64_t pixel_height;
      EbmlBin color_space;
      uint64_t stereo_mode;
  } MatroskaTrackVideo;
  
  typedef struct {
      double   samplerate;
      double   out_samplerate;
      uint64_t bitdepth;
      uint64_t channels;
  
      /* real audio header (extracted from extradata) */
      int      coded_framesize;
      int      sub_packet_h;
      int      frame_size;
      int      sub_packet_size;
      int      sub_packet_cnt;
      int      pkt_cnt;
      uint64_t buf_timecode;
      uint8_t *buf;
  } MatroskaTrackAudio;
  
  typedef struct {
      uint64_t uid;
      uint64_t type;
  } MatroskaTrackPlane;
  
  typedef struct {
      EbmlList combine_planes;
  } MatroskaTrackOperation;
  
  typedef struct {
      uint64_t num;
      uint64_t uid;
      uint64_t type;
      char    *name;
      char    *codec_id;
      EbmlBin  codec_priv;
      char    *language;
      double time_scale;
      uint64_t default_duration;
      uint64_t flag_default;
      uint64_t flag_forced;
      MatroskaTrackVideo video;
      MatroskaTrackAudio audio;
      MatroskaTrackOperation operation;
      EbmlList encodings;
  
      AVStream *stream;
      int64_t end_timecode;
      int ms_compat;
  } MatroskaTrack;
  
  typedef struct {
      uint64_t uid;
      char *filename;
      char *mime;
      EbmlBin bin;
  
      AVStream *stream;
  } MatroskaAttachement;
  
  typedef struct {
      uint64_t start;
      uint64_t end;
      uint64_t uid;
      char    *title;
  
      AVChapter *chapter;
  } MatroskaChapter;
  
  typedef struct {
      uint64_t track;
      uint64_t pos;
  } MatroskaIndexPos;
  
  typedef struct {
      uint64_t time;
      EbmlList pos;
  } MatroskaIndex;
  
  typedef struct {
      char *name;
      char *string;
      char *lang;
      uint64_t def;
      EbmlList sub;
  } MatroskaTag;
  
  typedef struct {
      char    *type;
      uint64_t typevalue;
      uint64_t trackuid;
      uint64_t chapteruid;
      uint64_t attachuid;
  } MatroskaTagTarget;
  
  typedef struct {
      MatroskaTagTarget target;
      EbmlList tag;
  } MatroskaTags;
  
  typedef struct {
      uint64_t id;
      uint64_t pos;
  } MatroskaSeekhead;
  
  typedef struct {
      uint64_t start;
      uint64_t length;
  } MatroskaLevel;
  
  typedef struct {
      AVFormatContext *ctx;
  
      /* EBML stuff */
      int num_levels;
      MatroskaLevel levels[EBML_MAX_DEPTH];
      int level_up;
      uint32_t current_id;
  
      uint64_t time_scale;
      double   duration;
      char    *title;
      EbmlList tracks;
      EbmlList attachments;
      EbmlList chapters;
      EbmlList index;
      EbmlList tags;
      EbmlList seekhead;
  
      /* byte position of the segment inside the stream */
      int64_t segment_start;
  
      /* the packet queue */
      AVPacket **packets;
      int num_packets;
      AVPacket *prev_pkt;
  
      int done;
  
      /* What to skip before effectively reading a packet. */
      int skip_to_keyframe;
      uint64_t skip_to_timecode;
  
      /* File has a CUES element, but we defer parsing until it is needed. */
      int cues_parsing_deferred;
  } MatroskaDemuxContext;
  
  typedef struct {
      uint64_t duration;
      int64_t  reference;
      uint64_t non_simple;
      EbmlBin  bin;
  } MatroskaBlock;
  
  typedef struct {
      uint64_t timecode;
      EbmlList blocks;
  } MatroskaCluster;
  
  static EbmlSyntax ebml_header[] = {
      { EBML_ID_EBMLREADVERSION,        EBML_UINT, 0, offsetof(Ebml,version), {.u=EBML_VERSION} },
      { EBML_ID_EBMLMAXSIZELENGTH,      EBML_UINT, 0, offsetof(Ebml,max_size), {.u=8} },
      { EBML_ID_EBMLMAXIDLENGTH,        EBML_UINT, 0, offsetof(Ebml,id_length), {.u=4} },
      { EBML_ID_DOCTYPE,                EBML_STR,  0, offsetof(Ebml,doctype), {.s="(none)"} },
      { EBML_ID_DOCTYPEREADVERSION,     EBML_UINT, 0, offsetof(Ebml,doctype_version), {.u=1} },
      { EBML_ID_EBMLVERSION,            EBML_NONE },
      { EBML_ID_DOCTYPEVERSION,         EBML_NONE },
      { 0 }
  };
  
  static EbmlSyntax ebml_syntax[] = {
      { EBML_ID_HEADER,                 EBML_NEST, 0, 0, {.n=ebml_header} },
      { 0 }
  };
  
  static EbmlSyntax matroska_info[] = {
      { MATROSKA_ID_TIMECODESCALE,      EBML_UINT,  0, offsetof(MatroskaDemuxContext,time_scale), {.u=1000000} },
      { MATROSKA_ID_DURATION,           EBML_FLOAT, 0, offsetof(MatroskaDemuxContext,duration) },
      { MATROSKA_ID_TITLE,              EBML_UTF8,  0, offsetof(MatroskaDemuxContext,title) },
      { MATROSKA_ID_WRITINGAPP,         EBML_NONE },
      { MATROSKA_ID_MUXINGAPP,          EBML_NONE },
      { MATROSKA_ID_DATEUTC,            EBML_NONE },
      { MATROSKA_ID_SEGMENTUID,         EBML_NONE },
      { 0 }
  };
  
  static EbmlSyntax matroska_track_video[] = {
      { MATROSKA_ID_VIDEOFRAMERATE,     EBML_FLOAT,0, offsetof(MatroskaTrackVideo,frame_rate) },
      { MATROSKA_ID_VIDEODISPLAYWIDTH,  EBML_UINT, 0, offsetof(MatroskaTrackVideo,display_width) },
      { MATROSKA_ID_VIDEODISPLAYHEIGHT, EBML_UINT, 0, offsetof(MatroskaTrackVideo,display_height) },
      { MATROSKA_ID_VIDEOPIXELWIDTH,    EBML_UINT, 0, offsetof(MatroskaTrackVideo,pixel_width) },
      { MATROSKA_ID_VIDEOPIXELHEIGHT,   EBML_UINT, 0, offsetof(MatroskaTrackVideo,pixel_height) },
      { MATROSKA_ID_VIDEOCOLORSPACE,    EBML_BIN,  0, offsetof(MatroskaTrackVideo,color_space) },
      { MATROSKA_ID_VIDEOSTEREOMODE,    EBML_UINT, 0, offsetof(MatroskaTrackVideo,stereo_mode) },
      { MATROSKA_ID_VIDEOPIXELCROPB,    EBML_NONE },
      { MATROSKA_ID_VIDEOPIXELCROPT,    EBML_NONE },
      { MATROSKA_ID_VIDEOPIXELCROPL,    EBML_NONE },
      { MATROSKA_ID_VIDEOPIXELCROPR,    EBML_NONE },
      { MATROSKA_ID_VIDEODISPLAYUNIT,   EBML_NONE },
      { MATROSKA_ID_VIDEOFLAGINTERLACED,EBML_NONE },
      { MATROSKA_ID_VIDEOASPECTRATIO,   EBML_NONE },
      { 0 }
  };
  
  static EbmlSyntax matroska_track_audio[] = {
      { MATROSKA_ID_AUDIOSAMPLINGFREQ,  EBML_FLOAT,0, offsetof(MatroskaTrackAudio,samplerate), {.f=8000.0} },
      { MATROSKA_ID_AUDIOOUTSAMPLINGFREQ,EBML_FLOAT,0,offsetof(MatroskaTrackAudio,out_samplerate) },
      { MATROSKA_ID_AUDIOBITDEPTH,      EBML_UINT, 0, offsetof(MatroskaTrackAudio,bitdepth) },
      { MATROSKA_ID_AUDIOCHANNELS,      EBML_UINT, 0, offsetof(MatroskaTrackAudio,channels), {.u=1} },
      { 0 }
  };
  
  static EbmlSyntax matroska_track_encoding_compression[] = {
      { MATROSKA_ID_ENCODINGCOMPALGO,   EBML_UINT, 0, offsetof(MatroskaTrackCompression,algo), {.u=0} },
      { MATROSKA_ID_ENCODINGCOMPSETTINGS,EBML_BIN, 0, offsetof(MatroskaTrackCompression,settings) },
      { 0 }
  };
  
  static EbmlSyntax matroska_track_encoding[] = {
      { MATROSKA_ID_ENCODINGSCOPE,      EBML_UINT, 0, offsetof(MatroskaTrackEncoding,scope), {.u=1} },
      { MATROSKA_ID_ENCODINGTYPE,       EBML_UINT, 0, offsetof(MatroskaTrackEncoding,type), {.u=0} },
      { MATROSKA_ID_ENCODINGCOMPRESSION,EBML_NEST, 0, offsetof(MatroskaTrackEncoding,compression), {.n=matroska_track_encoding_compression} },
      { MATROSKA_ID_ENCODINGORDER,      EBML_NONE },
      { 0 }
  };
  
  static EbmlSyntax matroska_track_encodings[] = {
      { MATROSKA_ID_TRACKCONTENTENCODING, EBML_NEST, sizeof(MatroskaTrackEncoding), offsetof(MatroskaTrack,encodings), {.n=matroska_track_encoding} },
      { 0 }
  };
  
  static EbmlSyntax matroska_track_plane[] = {
      { MATROSKA_ID_TRACKPLANEUID,  EBML_UINT, 0, offsetof(MatroskaTrackPlane,uid) },
      { MATROSKA_ID_TRACKPLANETYPE, EBML_UINT, 0, offsetof(MatroskaTrackPlane,type) },
      { 0 }
  };
  
  static EbmlSyntax matroska_track_combine_planes[] = {
      { MATROSKA_ID_TRACKPLANE, EBML_NEST, sizeof(MatroskaTrackPlane), offsetof(MatroskaTrackOperation,combine_planes), {.n=matroska_track_plane} },
      { 0 }
  };
  
  static EbmlSyntax matroska_track_operation[] = {
      { MATROSKA_ID_TRACKCOMBINEPLANES, EBML_NEST, 0, 0, {.n=matroska_track_combine_planes} },
      { 0 }
  };
  
  static EbmlSyntax matroska_track[] = {
      { MATROSKA_ID_TRACKNUMBER,          EBML_UINT, 0, offsetof(MatroskaTrack,num) },
      { MATROSKA_ID_TRACKNAME,            EBML_UTF8, 0, offsetof(MatroskaTrack,name) },
      { MATROSKA_ID_TRACKUID,             EBML_UINT, 0, offsetof(MatroskaTrack,uid) },
      { MATROSKA_ID_TRACKTYPE,            EBML_UINT, 0, offsetof(MatroskaTrack,type) },
      { MATROSKA_ID_CODECID,              EBML_STR,  0, offsetof(MatroskaTrack,codec_id) },
      { MATROSKA_ID_CODECPRIVATE,         EBML_BIN,  0, offsetof(MatroskaTrack,codec_priv) },
      { MATROSKA_ID_TRACKLANGUAGE,        EBML_UTF8, 0, offsetof(MatroskaTrack,language), {.s="eng"} },
      { MATROSKA_ID_TRACKDEFAULTDURATION, EBML_UINT, 0, offsetof(MatroskaTrack,default_duration) },
      { MATROSKA_ID_TRACKTIMECODESCALE,   EBML_FLOAT,0, offsetof(MatroskaTrack,time_scale), {.f=1.0} },
      { MATROSKA_ID_TRACKFLAGDEFAULT,     EBML_UINT, 0, offsetof(MatroskaTrack,flag_default), {.u=1} },
      { MATROSKA_ID_TRACKFLAGFORCED,      EBML_UINT, 0, offsetof(MatroskaTrack,flag_forced), {.u=0} },
      { MATROSKA_ID_TRACKVIDEO,           EBML_NEST, 0, offsetof(MatroskaTrack,video), {.n=matroska_track_video} },
      { MATROSKA_ID_TRACKAUDIO,           EBML_NEST, 0, offsetof(MatroskaTrack,audio), {.n=matroska_track_audio} },
      { MATROSKA_ID_TRACKOPERATION,       EBML_NEST, 0, offsetof(MatroskaTrack,operation), {.n=matroska_track_operation} },
      { MATROSKA_ID_TRACKCONTENTENCODINGS,EBML_NEST, 0, 0, {.n=matroska_track_encodings} },
      { MATROSKA_ID_TRACKFLAGENABLED,     EBML_NONE },
      { MATROSKA_ID_TRACKFLAGLACING,      EBML_NONE },
      { MATROSKA_ID_CODECNAME,            EBML_NONE },
      { MATROSKA_ID_CODECDECODEALL,       EBML_NONE },
      { MATROSKA_ID_CODECINFOURL,         EBML_NONE },
      { MATROSKA_ID_CODECDOWNLOADURL,     EBML_NONE },
      { MATROSKA_ID_TRACKMINCACHE,        EBML_NONE },
      { MATROSKA_ID_TRACKMAXCACHE,        EBML_NONE },
      { MATROSKA_ID_TRACKMAXBLKADDID,     EBML_NONE },
      { 0 }
  };
  
  static EbmlSyntax matroska_tracks[] = {
      { MATROSKA_ID_TRACKENTRY,         EBML_NEST, sizeof(MatroskaTrack), offsetof(MatroskaDemuxContext,tracks), {.n=matroska_track} },
      { 0 }
  };
  
  static EbmlSyntax matroska_attachment[] = {
      { MATROSKA_ID_FILEUID,            EBML_UINT, 0, offsetof(MatroskaAttachement,uid) },
      { MATROSKA_ID_FILENAME,           EBML_UTF8, 0, offsetof(MatroskaAttachement,filename) },
      { MATROSKA_ID_FILEMIMETYPE,       EBML_STR,  0, offsetof(MatroskaAttachement,mime) },
      { MATROSKA_ID_FILEDATA,           EBML_BIN,  0, offsetof(MatroskaAttachement,bin) },
      { MATROSKA_ID_FILEDESC,           EBML_NONE },
      { 0 }
  };
  
  static EbmlSyntax matroska_attachments[] = {
      { MATROSKA_ID_ATTACHEDFILE,       EBML_NEST, sizeof(MatroskaAttachement), offsetof(MatroskaDemuxContext,attachments), {.n=matroska_attachment} },
      { 0 }
  };
  
  static EbmlSyntax matroska_chapter_display[] = {
      { MATROSKA_ID_CHAPSTRING,         EBML_UTF8, 0, offsetof(MatroskaChapter,title) },
      { MATROSKA_ID_CHAPLANG,           EBML_NONE },
      { 0 }
  };
  
  static EbmlSyntax matroska_chapter_entry[] = {
      { MATROSKA_ID_CHAPTERTIMESTART,   EBML_UINT, 0, offsetof(MatroskaChapter,start), {.u=AV_NOPTS_VALUE} },
      { MATROSKA_ID_CHAPTERTIMEEND,     EBML_UINT, 0, offsetof(MatroskaChapter,end), {.u=AV_NOPTS_VALUE} },
      { MATROSKA_ID_CHAPTERUID,         EBML_UINT, 0, offsetof(MatroskaChapter,uid) },
      { MATROSKA_ID_CHAPTERDISPLAY,     EBML_NEST, 0, 0, {.n=matroska_chapter_display} },
      { MATROSKA_ID_CHAPTERFLAGHIDDEN,  EBML_NONE },
      { MATROSKA_ID_CHAPTERFLAGENABLED, EBML_NONE },
      { MATROSKA_ID_CHAPTERPHYSEQUIV,   EBML_NONE },
      { MATROSKA_ID_CHAPTERATOM,        EBML_NONE },
      { 0 }
  };
  
  static EbmlSyntax matroska_chapter[] = {
      { MATROSKA_ID_CHAPTERATOM,        EBML_NEST, sizeof(MatroskaChapter), offsetof(MatroskaDemuxContext,chapters), {.n=matroska_chapter_entry} },
      { MATROSKA_ID_EDITIONUID,         EBML_NONE },
      { MATROSKA_ID_EDITIONFLAGHIDDEN,  EBML_NONE },
      { MATROSKA_ID_EDITIONFLAGDEFAULT, EBML_NONE },
      { MATROSKA_ID_EDITIONFLAGORDERED, EBML_NONE },
      { 0 }
  };
  
  static EbmlSyntax matroska_chapters[] = {
      { MATROSKA_ID_EDITIONENTRY,       EBML_NEST, 0, 0, {.n=matroska_chapter} },
      { 0 }
  };
  
  static EbmlSyntax matroska_index_pos[] = {
      { MATROSKA_ID_CUETRACK,           EBML_UINT, 0, offsetof(MatroskaIndexPos,track) },
      { MATROSKA_ID_CUECLUSTERPOSITION, EBML_UINT, 0, offsetof(MatroskaIndexPos,pos)   },
      { MATROSKA_ID_CUEBLOCKNUMBER,     EBML_NONE },
      { 0 }
  };
  
  static EbmlSyntax matroska_index_entry[] = {
      { MATROSKA_ID_CUETIME,            EBML_UINT, 0, offsetof(MatroskaIndex,time) },
      { MATROSKA_ID_CUETRACKPOSITION,   EBML_NEST, sizeof(MatroskaIndexPos), offsetof(MatroskaIndex,pos), {.n=matroska_index_pos} },
      { 0 }
  };
  
  static EbmlSyntax matroska_index[] = {
      { MATROSKA_ID_POINTENTRY,         EBML_NEST, sizeof(MatroskaIndex), offsetof(MatroskaDemuxContext,index), {.n=matroska_index_entry} },
      { 0 }
  };
  
  static EbmlSyntax matroska_simpletag[] = {
      { MATROSKA_ID_TAGNAME,            EBML_UTF8, 0, offsetof(MatroskaTag,name) },
      { MATROSKA_ID_TAGSTRING,          EBML_UTF8, 0, offsetof(MatroskaTag,string) },
      { MATROSKA_ID_TAGLANG,            EBML_STR,  0, offsetof(MatroskaTag,lang), {.s="und"} },
      { MATROSKA_ID_TAGDEFAULT,         EBML_UINT, 0, offsetof(MatroskaTag,def) },
      { MATROSKA_ID_TAGDEFAULT_BUG,     EBML_UINT, 0, offsetof(MatroskaTag,def) },
      { MATROSKA_ID_SIMPLETAG,          EBML_NEST, sizeof(MatroskaTag), offsetof(MatroskaTag,sub), {.n=matroska_simpletag} },
      { 0 }
  };
  
  static EbmlSyntax matroska_tagtargets[] = {
      { MATROSKA_ID_TAGTARGETS_TYPE,      EBML_STR,  0, offsetof(MatroskaTagTarget,type) },
      { MATROSKA_ID_TAGTARGETS_TYPEVALUE, EBML_UINT, 0, offsetof(MatroskaTagTarget,typevalue), {.u=50} },
      { MATROSKA_ID_TAGTARGETS_TRACKUID,  EBML_UINT, 0, offsetof(MatroskaTagTarget,trackuid) },
      { MATROSKA_ID_TAGTARGETS_CHAPTERUID,EBML_UINT, 0, offsetof(MatroskaTagTarget,chapteruid) },
      { MATROSKA_ID_TAGTARGETS_ATTACHUID, EBML_UINT, 0, offsetof(MatroskaTagTarget,attachuid) },
      { 0 }
  };
  
  static EbmlSyntax matroska_tag[] = {
      { MATROSKA_ID_SIMPLETAG,          EBML_NEST, sizeof(MatroskaTag), offsetof(MatroskaTags,tag), {.n=matroska_simpletag} },
      { MATROSKA_ID_TAGTARGETS,         EBML_NEST, 0, offsetof(MatroskaTags,target), {.n=matroska_tagtargets} },
      { 0 }
  };
  
  static EbmlSyntax matroska_tags[] = {
      { MATROSKA_ID_TAG,                EBML_NEST, sizeof(MatroskaTags), offsetof(MatroskaDemuxContext,tags), {.n=matroska_tag} },
      { 0 }
  };
  
  static EbmlSyntax matroska_seekhead_entry[] = {
      { MATROSKA_ID_SEEKID,             EBML_UINT, 0, offsetof(MatroskaSeekhead,id) },
      { MATROSKA_ID_SEEKPOSITION,       EBML_UINT, 0, offsetof(MatroskaSeekhead,pos), {.u=-1} },
      { 0 }
  };
  
  static EbmlSyntax matroska_seekhead[] = {
      { MATROSKA_ID_SEEKENTRY,          EBML_NEST, sizeof(MatroskaSeekhead), offsetof(MatroskaDemuxContext,seekhead), {.n=matroska_seekhead_entry} },
      { 0 }
  };
  
  static EbmlSyntax matroska_segment[] = {
      { MATROSKA_ID_INFO,           EBML_NEST, 0, 0, {.n=matroska_info       } },
      { MATROSKA_ID_TRACKS,         EBML_NEST, 0, 0, {.n=matroska_tracks     } },
      { MATROSKA_ID_ATTACHMENTS,    EBML_NEST, 0, 0, {.n=matroska_attachments} },
      { MATROSKA_ID_CHAPTERS,       EBML_NEST, 0, 0, {.n=matroska_chapters   } },
      { MATROSKA_ID_CUES,           EBML_NEST, 0, 0, {.n=matroska_index      } },
      { MATROSKA_ID_TAGS,           EBML_NEST, 0, 0, {.n=matroska_tags       } },
      { MATROSKA_ID_SEEKHEAD,       EBML_NEST, 0, 0, {.n=matroska_seekhead   } },
      { MATROSKA_ID_CLUSTER,        EBML_STOP },
      { 0 }
  };
  
  static EbmlSyntax matroska_segments[] = {
      { MATROSKA_ID_SEGMENT,        EBML_NEST, 0, 0, {.n=matroska_segment    } },
      { 0 }
  };
  
  static EbmlSyntax matroska_blockgroup[] = {
      { MATROSKA_ID_BLOCK,          EBML_BIN,  0, offsetof(MatroskaBlock,bin) },
      { MATROSKA_ID_SIMPLEBLOCK,    EBML_BIN,  0, offsetof(MatroskaBlock,bin) },
      { MATROSKA_ID_BLOCKDURATION,  EBML_UINT, 0, offsetof(MatroskaBlock,duration) },
      { MATROSKA_ID_BLOCKREFERENCE, EBML_UINT, 0, offsetof(MatroskaBlock,reference) },
      { 1,                          EBML_UINT, 0, offsetof(MatroskaBlock,non_simple), {.u=1} },
      { 0 }
  };
  
  static EbmlSyntax matroska_cluster[] = {
      { MATROSKA_ID_CLUSTERTIMECODE,EBML_UINT,0, offsetof(MatroskaCluster,timecode) },
      { MATROSKA_ID_BLOCKGROUP,     EBML_NEST, sizeof(MatroskaBlock), offsetof(MatroskaCluster,blocks), {.n=matroska_blockgroup} },
      { MATROSKA_ID_SIMPLEBLOCK,    EBML_PASS, sizeof(MatroskaBlock), offsetof(MatroskaCluster,blocks), {.n=matroska_blockgroup} },
      { MATROSKA_ID_CLUSTERPOSITION,EBML_NONE },
      { MATROSKA_ID_CLUSTERPREVSIZE,EBML_NONE },
      { 0 }
  };
  
  static EbmlSyntax matroska_clusters[] = {
      { MATROSKA_ID_CLUSTER,        EBML_NEST, 0, 0, {.n=matroska_cluster} },
      { MATROSKA_ID_INFO,           EBML_NONE },
      { MATROSKA_ID_CUES,           EBML_NONE },
      { MATROSKA_ID_TAGS,           EBML_NONE },
      { MATROSKA_ID_SEEKHEAD,       EBML_NONE },
      { 0 }
  };
  
  static const char *matroska_doctypes[] = { "matroska", "webm" };
  
  /*
   * Return: Whether we reached the end of a level in the hierarchy or not.
   */
  static int ebml_level_end(MatroskaDemuxContext *matroska)
  {
      AVIOContext *pb = matroska->ctx->pb;
      int64_t pos = avio_tell(pb);
  
      if (matroska->num_levels > 0) {
          MatroskaLevel *level = &matroska->levels[matroska->num_levels - 1];
          if (pos - level->start >= level->length || matroska->current_id) {
              matroska->num_levels--;
              return 1;
          }
      }
      return 0;
  }
  
  /*
   * Read: an "EBML number", which is defined as a variable-length
   * array of bytes. The first byte indicates the length by giving a
   * number of 0-bits followed by a one. The position of the first
   * "one" bit inside the first byte indicates the length of this
   * number.
   * Returns: number of bytes read, < 0 on error
   */
  static int ebml_read_num(MatroskaDemuxContext *matroska, AVIOContext *pb,
                           int max_size, uint64_t *number)
  {
      int read = 1, n = 1;
      uint64_t total = 0;
  
      /* The first byte tells us the length in bytes - avio_r8() can normally
       * return 0, but since that's not a valid first ebmlID byte, we can
       * use it safely here to catch EOS. */
      if (!(total = avio_r8(pb))) {
          /* we might encounter EOS here */
          if (!url_feof(pb)) {
              int64_t pos = avio_tell(pb);
              av_log(matroska->ctx, AV_LOG_ERROR,
                     "Read error at pos. %"PRIu64" (0x%"PRIx64")\n",
                     pos, pos);
          }
          return AVERROR(EIO); /* EOS or actual I/O error */
      }
  
      /* get the length of the EBML number */
      read = 8 - ff_log2_tab[total];
      if (read > max_size) {
          int64_t pos = avio_tell(pb) - 1;
          av_log(matroska->ctx, AV_LOG_ERROR,
                 "Invalid EBML number size tag 0x%02x at pos %"PRIu64" (0x%"PRIx64")\n",
                 (uint8_t) total, pos, pos);
          return AVERROR_INVALIDDATA;
      }
  
      /* read out length */
      total ^= 1 << ff_log2_tab[total];
      while (n++ < read)
          total = (total << 8) | avio_r8(pb);
  
      *number = total;
  
      return read;
  }
  
  /**
   * Read a EBML length value.
   * This needs special handling for the "unknown length" case which has multiple
   * encodings.
   */
  static int ebml_read_length(MatroskaDemuxContext *matroska, AVIOContext *pb,
                              uint64_t *number)
  {
      int res = ebml_read_num(matroska, pb, 8, number);
      if (res > 0 && *number + 1 == 1ULL << (7 * res))
          *number = 0xffffffffffffffULL;
      return res;
  }
  
  /*
   * Read the next element as an unsigned int.
   * 0 is success, < 0 is failure.
   */
  static int ebml_read_uint(AVIOContext *pb, int size, uint64_t *num)
  {
      int n = 0;
  
      if (size > 8)
          return AVERROR_INVALIDDATA;
  
      /* big-endian ordering; build up number */
      *num = 0;
      while (n++ < size)
          *num = (*num << 8) | avio_r8(pb);
  
      return 0;
  }
  
  /*
   * Read the next element as a float.
   * 0 is success, < 0 is failure.
   */
  static int ebml_read_float(AVIOContext *pb, int size, double *num)
  {
      if (size == 0) {
          *num = 0;
      } else if (size == 4) {
          *num = av_int2float(avio_rb32(pb));
      } else if (size == 8){
          *num = av_int2double(avio_rb64(pb));
      } else
          return AVERROR_INVALIDDATA;
  
      return 0;
  }
  
  /*
   * Read the next element as an ASCII string.
   * 0 is success, < 0 is failure.
   */
  static int ebml_read_ascii(AVIOContext *pb, int size, char **str)
  {
      av_free(*str);
      /* EBML strings are usually not 0-terminated, so we allocate one
       * byte more, read the string and NULL-terminate it ourselves. */
      if (!(*str = av_malloc(size + 1)))
          return AVERROR(ENOMEM);
      if (avio_read(pb, (uint8_t *) *str, size) != size) {
          av_freep(str);
          return AVERROR(EIO);
      }
      (*str)[size] = '\0';
  
      return 0;
  }
  
  /*
   * Read the next element as binary data.
   * 0 is success, < 0 is failure.
   */
  static int ebml_read_binary(AVIOContext *pb, int length, EbmlBin *bin)
  {
      av_free(bin->data);
      if (!(bin->data = av_malloc(length)))
          return AVERROR(ENOMEM);
  
      bin->size = length;
      bin->pos  = avio_tell(pb);
      if (avio_read(pb, bin->data, length) != length) {
          av_freep(&bin->data);
          return AVERROR(EIO);
      }
  
      return 0;
  }
  
  /*
   * Read the next element, but only the header. The contents
   * are supposed to be sub-elements which can be read separately.
   * 0 is success, < 0 is failure.
   */
  static int ebml_read_master(MatroskaDemuxContext *matroska, uint64_t length)
  {
      AVIOContext *pb = matroska->ctx->pb;
      MatroskaLevel *level;
  
      if (matroska->num_levels >= EBML_MAX_DEPTH) {
          av_log(matroska->ctx, AV_LOG_ERROR,
                 "File moves beyond max. allowed depth (%d)\n", EBML_MAX_DEPTH);
          return AVERROR(ENOSYS);
      }
  
      level = &matroska->levels[matroska->num_levels++];
      level->start = avio_tell(pb);
      level->length = length;
  
      return 0;
  }
  
  /*
   * Read signed/unsigned "EBML" numbers.
   * Return: number of bytes processed, < 0 on error
   */
  static int matroska_ebmlnum_uint(MatroskaDemuxContext *matroska,
                                   uint8_t *data, uint32_t size, uint64_t *num)
  {
      AVIOContext pb;
      ffio_init_context(&pb, data, size, 0, NULL, NULL, NULL, NULL);
      return ebml_read_num(matroska, &pb, FFMIN(size, 8), num);
  }
  
  /*
   * Same as above, but signed.
   */
  static int matroska_ebmlnum_sint(MatroskaDemuxContext *matroska,
                                   uint8_t *data, uint32_t size, int64_t *num)
  {
      uint64_t unum;
      int res;
  
      /* read as unsigned number first */
      if ((res = matroska_ebmlnum_uint(matroska, data, size, &unum)) < 0)
          return res;
  
      /* make signed (weird way) */
      *num = unum - ((1LL << (7*res - 1)) - 1);
  
      return res;
  }
  
  static int ebml_parse_elem(MatroskaDemuxContext *matroska,
                             EbmlSyntax *syntax, void *data);
  
  static int ebml_parse_id(MatroskaDemuxContext *matroska, EbmlSyntax *syntax,
                           uint32_t id, void *data)
  {
      int i;
      for (i=0; syntax[i].id; i++)
          if (id == syntax[i].id)
              break;
      if (!syntax[i].id && id == MATROSKA_ID_CLUSTER &&
          matroska->num_levels > 0 &&
          matroska->levels[matroska->num_levels-1].length == 0xffffffffffffff)
          return 0;  // we reached the end of an unknown size cluster
      if (!syntax[i].id && id != EBML_ID_VOID && id != EBML_ID_CRC32)
          av_log(matroska->ctx, AV_LOG_INFO, "Unknown entry 0x%X\n", id);
      return ebml_parse_elem(matroska, &syntax[i], data);
  }
  
  static int ebml_parse(MatroskaDemuxContext *matroska, EbmlSyntax *syntax,
                        void *data)
  {
      if (!matroska->current_id) {
          uint64_t id;
          int res = ebml_read_num(matroska, matroska->ctx->pb, 4, &id);
          if (res < 0)
              return res;
          matroska->current_id = id | 1 << 7*res;
      }
      return ebml_parse_id(matroska, syntax, matroska->current_id, data);
  }
  
  static int ebml_parse_nest(MatroskaDemuxContext *matroska, EbmlSyntax *syntax,
                             void *data)
  {
      int i, res = 0;
  
      for (i=0; syntax[i].id; i++)
          switch (syntax[i].type) {
          case EBML_UINT:
              *(uint64_t *)((char *)data+syntax[i].data_offset) = syntax[i].def.u;
              break;
          case EBML_FLOAT:
              *(double   *)((char *)data+syntax[i].data_offset) = syntax[i].def.f;
              break;
          case EBML_STR:
          case EBML_UTF8:
              *(char    **)((char *)data+syntax[i].data_offset) = av_strdup(syntax[i].def.s);
              break;
          }
  
      while (!res && !ebml_level_end(matroska))
          res = ebml_parse(matroska, syntax, data);
  
      return res;
  }
  
  static int ebml_parse_elem(MatroskaDemuxContext *matroska,
                             EbmlSyntax *syntax, void *data)
  {
      static const uint64_t max_lengths[EBML_TYPE_COUNT] = {
          [EBML_UINT]  = 8,
          [EBML_FLOAT] = 8,
          // max. 16 MB for strings
          [EBML_STR]   = 0x1000000,
          [EBML_UTF8]  = 0x1000000,
          // max. 256 MB for binary data
          [EBML_BIN]   = 0x10000000,
          // no limits for anything else
      };
      AVIOContext *pb = matroska->ctx->pb;
      uint32_t id = syntax->id;
      uint64_t length;
      int res;
      void *newelem;
  
      data = (char *)data + syntax->data_offset;
      if (syntax->list_elem_size) {
          EbmlList *list = data;
          newelem = av_realloc(list->elem, (list->nb_elem+1)*syntax->list_elem_size);
          if (!newelem)
              return AVERROR(ENOMEM);
          list->elem = newelem;
          data = (char*)list->elem + list->nb_elem*syntax->list_elem_size;
          memset(data, 0, syntax->list_elem_size);
          list->nb_elem++;
      }
  
      if (syntax->type != EBML_PASS && syntax->type != EBML_STOP) {
          matroska->current_id = 0;
          if ((res = ebml_read_length(matroska, pb, &length)) < 0)
              return res;
          if (max_lengths[syntax->type] && length > max_lengths[syntax->type]) {
              av_log(matroska->ctx, AV_LOG_ERROR,
                     "Invalid length 0x%"PRIx64" > 0x%"PRIx64" for syntax element %i\n",
                     length, max_lengths[syntax->type], syntax->type);
              return AVERROR_INVALIDDATA;
          }
      }
  
      switch (syntax->type) {
      case EBML_UINT:  res = ebml_read_uint  (pb, length, data);  break;
      case EBML_FLOAT: res = ebml_read_float (pb, length, data);  break;
      case EBML_STR:
      case EBML_UTF8:  res = ebml_read_ascii (pb, length, data);  break;
      case EBML_BIN:   res = ebml_read_binary(pb, length, data);  break;
      case EBML_NEST:  if ((res=ebml_read_master(matroska, length)) < 0)
                           return res;
                       if (id == MATROSKA_ID_SEGMENT)
                           matroska->segment_start = avio_tell(matroska->ctx->pb);
                       return ebml_parse_nest(matroska, syntax->def.n, data);
      case EBML_PASS:  return ebml_parse_id(matroska, syntax->def.n, id, data);
      case EBML_STOP:  return 1;
      default:         return avio_skip(pb,length)<0 ? AVERROR(EIO) : 0;
      }
      if (res == AVERROR_INVALIDDATA)
          av_log(matroska->ctx, AV_LOG_ERROR, "Invalid element\n");
      else if (res == AVERROR(EIO))
          av_log(matroska->ctx, AV_LOG_ERROR, "Read error\n");
      return res;
  }
  
  static void ebml_free(EbmlSyntax *syntax, void *data)
  {
      int i, j;
      for (i=0; syntax[i].id; i++) {
          void *data_off = (char *)data + syntax[i].data_offset;
          switch (syntax[i].type) {
          case EBML_STR:
          case EBML_UTF8:  av_freep(data_off);                      break;
          case EBML_BIN:   av_freep(&((EbmlBin *)data_off)->data);  break;
          case EBML_NEST:
              if (syntax[i].list_elem_size) {
                  EbmlList *list = data_off;
                  char *ptr = list->elem;
                  for (j=0; j<list->nb_elem; j++, ptr+=syntax[i].list_elem_size)
                      ebml_free(syntax[i].def.n, ptr);
                  av_free(list->elem);
              } else
                  ebml_free(syntax[i].def.n, data_off);
          default:  break;
          }
      }
  }
  
  
  /*
   * Autodetecting...
   */
  static int matroska_probe(AVProbeData *p)
  {
      uint64_t total = 0;
      int len_mask = 0x80, size = 1, n = 1, i;
  
      /* EBML header? */
      if (AV_RB32(p->buf) != EBML_ID_HEADER)
          return 0;
  
      /* length of header */
      total = p->buf[4];
      while (size <= 8 && !(total & len_mask)) {
          size++;
          len_mask >>= 1;
      }
      if (size > 8)
        return 0;
      total &= (len_mask - 1);
      while (n < size)
          total = (total << 8) | p->buf[4 + n++];
  
      /* Does the probe data contain the whole header? */
      if (p->buf_size < 4 + size + total)
        return 0;
  
      /* The header should contain a known document type. For now,
       * we don't parse the whole header but simply check for the
       * availability of that array of characters inside the header.
       * Not fully fool-proof, but good enough. */
      for (i = 0; i < FF_ARRAY_ELEMS(matroska_doctypes); i++) {
          int probelen = strlen(matroska_doctypes[i]);
          if (total < probelen)
              continue;
          for (n = 4+size; n <= 4+size+total-probelen; n++)
              if (!memcmp(p->buf+n, matroska_doctypes[i], probelen))
                  return AVPROBE_SCORE_MAX;
      }
  
      // probably valid EBML header but no recognized doctype
      return AVPROBE_SCORE_MAX/2;
  }
  
  static MatroskaTrack *matroska_find_track_by_num(MatroskaDemuxContext *matroska,
                                                   int num)
  {
      MatroskaTrack *tracks = matroska->tracks.elem;
      int i;
  
      for (i=0; i < matroska->tracks.nb_elem; i++)
          if (tracks[i].num == num)
              return &tracks[i];
  
      av_log(matroska->ctx, AV_LOG_ERROR, "Invalid track number %d\n", num);
      return NULL;
  }
  
  static int matroska_decode_buffer(uint8_t** buf, int* buf_size,
                                    MatroskaTrack *track)
  {
      MatroskaTrackEncoding *encodings = track->encodings.elem;
      uint8_t* data = *buf;
      int isize = *buf_size;
      uint8_t* pkt_data = NULL;
      uint8_t* newpktdata;
      int pkt_size = isize;
      int result = 0;
      int olen;
  
      if (pkt_size >= 10000000)
          return -1;
  
      switch (encodings[0].compression.algo) {
      case MATROSKA_TRACK_ENCODING_COMP_HEADERSTRIP:
          return encodings[0].compression.settings.size;
      case MATROSKA_TRACK_ENCODING_COMP_LZO:
          do {
              olen = pkt_size *= 3;
              pkt_data = av_realloc(pkt_data, pkt_size+AV_LZO_OUTPUT_PADDING);
              result = av_lzo1x_decode(pkt_data, &olen, data, &isize);
          } while (result==AV_LZO_OUTPUT_FULL && pkt_size<10000000);
          if (result)
              goto failed;
          pkt_size -= olen;
          break;
  #if CONFIG_ZLIB
      case MATROSKA_TRACK_ENCODING_COMP_ZLIB: {
          z_stream zstream = {0};
          if (inflateInit(&zstream) != Z_OK)
              return -1;
          zstream.next_in = data;
          zstream.avail_in = isize;
          do {
              pkt_size *= 3;
              newpktdata = av_realloc(pkt_data, pkt_size);
              if (!newpktdata) {
                  inflateEnd(&zstream);
                  goto failed;
              }
              pkt_data = newpktdata;
              zstream.avail_out = pkt_size - zstream.total_out;
              zstream.next_out = pkt_data + zstream.total_out;
              if (pkt_data) {
                  result = inflate(&zstream, Z_NO_FLUSH);
              } else
                  result = Z_MEM_ERROR;
          } while (result==Z_OK && pkt_size<10000000);
          pkt_size = zstream.total_out;
          inflateEnd(&zstream);
          if (result != Z_STREAM_END)
              goto failed;
          break;
      }
  #endif
  #if CONFIG_BZLIB
      case MATROSKA_TRACK_ENCODING_COMP_BZLIB: {
          bz_stream bzstream = {0};
          if (BZ2_bzDecompressInit(&bzstream, 0, 0) != BZ_OK)
              return -1;
          bzstream.next_in = data;
          bzstream.avail_in = isize;
          do {
              pkt_size *= 3;
              newpktdata = av_realloc(pkt_data, pkt_size);
              if (!newpktdata) {
                  BZ2_bzDecompressEnd(&bzstream);
                  goto failed;
              }
              pkt_data = newpktdata;
              bzstream.avail_out = pkt_size - bzstream.total_out_lo32;
              bzstream.next_out = pkt_data + bzstream.total_out_lo32;
              if (pkt_data) {
                  result = BZ2_bzDecompress(&bzstream);
              } else
                  result = BZ_MEM_ERROR;
          } while (result==BZ_OK && pkt_size<10000000);
          pkt_size = bzstream.total_out_lo32;
          BZ2_bzDecompressEnd(&bzstream);
          if (result != BZ_STREAM_END)
              goto failed;
          break;
      }
  #endif
      default:
          return -1;
      }
  
      *buf = pkt_data;
      *buf_size = pkt_size;
      return 0;
   failed:
      av_free(pkt_data);
      return -1;
  }
  
  static void matroska_fix_ass_packet(MatroskaDemuxContext *matroska,
                                      AVPacket *pkt, uint64_t display_duration)
  {
      char *line, *layer, *ptr = pkt->data, *end = ptr+pkt->size;
      for (; *ptr!=',' && ptr<end-1; ptr++);
      if (*ptr == ',')
          ptr++;
      layer = ptr;
      for (; *ptr!=',' && ptr<end-1; ptr++);
      if (*ptr == ',') {
          int64_t end_pts = pkt->pts + display_duration;
          int sc = matroska->time_scale * pkt->pts / 10000000;
          int ec = matroska->time_scale * end_pts  / 10000000;
          int sh, sm, ss, eh, em, es, len;
          sh = sc/360000;  sc -= 360000*sh;
          sm = sc/  6000;  sc -=   6000*sm;
          ss = sc/   100;  sc -=    100*ss;
          eh = ec/360000;  ec -= 360000*eh;
          em = ec/  6000;  ec -=   6000*em;
          es = ec/   100;  ec -=    100*es;
          *ptr++ = '\0';
          len = 50 + end-ptr + FF_INPUT_BUFFER_PADDING_SIZE;
          if (!(line = av_malloc(len)))
              return;
          snprintf(line,len,"Dialogue: %s,%d:%02d:%02d.%02d,%d:%02d:%02d.%02d,%s\r\n",
                   layer, sh, sm, ss, sc, eh, em, es, ec, ptr);
          av_free(pkt->data);
          pkt->data = line;
          pkt->size = strlen(line);
      }
  }
  
  static int matroska_merge_packets(AVPacket *out, AVPacket *in)
  {
      void *newdata = av_realloc(out->data, out->size+in->size);
      if (!newdata)
          return AVERROR(ENOMEM);
      out->data = newdata;
      memcpy(out->data+out->size, in->data, in->size);
      out->size += in->size;
      av_destruct_packet(in);
      av_free(in);
      return 0;
  }
  
  static void matroska_convert_tag(AVFormatContext *s, EbmlList *list,
                                   AVDictionary **metadata, char *prefix)
  {
      MatroskaTag *tags = list->elem;
      char key[1024];
      int i;
  
      for (i=0; i < list->nb_elem; i++) {
          const char *lang = strcmp(tags[i].lang, "und") ? tags[i].lang : NULL;
  
          if (!tags[i].name) {
              av_log(s, AV_LOG_WARNING, "Skipping invalid tag with no TagName.\n");
              continue;
          }
          if (prefix)  snprintf(key, sizeof(key), "%s/%s", prefix, tags[i].name);
          else         av_strlcpy(key, tags[i].name, sizeof(key));
          if (tags[i].def || !lang) {
          av_dict_set(metadata, key, tags[i].string, 0);
          if (tags[i].sub.nb_elem)
              matroska_convert_tag(s, &tags[i].sub, metadata, key);
          }
          if (lang) {
              av_strlcat(key, "-", sizeof(key));
              av_strlcat(key, lang, sizeof(key));
              av_dict_set(metadata, key, tags[i].string, 0);
              if (tags[i].sub.nb_elem)
                  matroska_convert_tag(s, &tags[i].sub, metadata, key);
          }
      }
      ff_metadata_conv(metadata, NULL, ff_mkv_metadata_conv);
  }
  
  static void matroska_convert_tags(AVFormatContext *s)
  {
      MatroskaDemuxContext *matroska = s->priv_data;
      MatroskaTags *tags = matroska->tags.elem;
      int i, j;
  
      for (i=0; i < matroska->tags.nb_elem; i++) {
          if (tags[i].target.attachuid) {
              MatroskaAttachement *attachment = matroska->attachments.elem;
              for (j=0; j<matroska->attachments.nb_elem; j++)
                  if (attachment[j].uid == tags[i].target.attachuid
                      && attachment[j].stream)
                      matroska_convert_tag(s, &tags[i].tag,
                                           &attachment[j].stream->metadata, NULL);
          } else if (tags[i].target.chapteruid) {
              MatroskaChapter *chapter = matroska->chapters.elem;
              for (j=0; j<matroska->chapters.nb_elem; j++)
                  if (chapter[j].uid == tags[i].target.chapteruid
                      && chapter[j].chapter)
                      matroska_convert_tag(s, &tags[i].tag,
                                           &chapter[j].chapter->metadata, NULL);
          } else if (tags[i].target.trackuid) {
              MatroskaTrack *track = matroska->tracks.elem;
              for (j=0; j<matroska->tracks.nb_elem; j++)
                  if (track[j].uid == tags[i].target.trackuid && track[j].stream)
                      matroska_convert_tag(s, &tags[i].tag,
                                           &track[j].stream->metadata, NULL);
          } else {
              matroska_convert_tag(s, &tags[i].tag, &s->metadata,
                                   tags[i].target.type);
          }
      }
  }
  
  static int matroska_parse_seekhead_entry(MatroskaDemuxContext *matroska, int idx)
  {
      EbmlList *seekhead_list = &matroska->seekhead;
      MatroskaSeekhead *seekhead = seekhead_list->elem;
      uint32_t level_up = matroska->level_up;
      int64_t before_pos = avio_tell(matroska->ctx->pb);
      uint32_t saved_id = matroska->current_id;
      MatroskaLevel level;
      int64_t offset;
      int ret = 0;
  
      if (idx >= seekhead_list->nb_elem
              || seekhead[idx].id == MATROSKA_ID_SEEKHEAD
              || seekhead[idx].id == MATROSKA_ID_CLUSTER)
          return 0;
  
      /* seek */
      offset = seekhead[idx].pos + matroska->segment_start;
      if (avio_seek(matroska->ctx->pb, offset, SEEK_SET) == offset) {
          /* We don't want to lose our seekhead level, so we add
           * a dummy. This is a crude hack. */
          if (matroska->num_levels == EBML_MAX_DEPTH) {
              av_log(matroska->ctx, AV_LOG_INFO,
                     "Max EBML element depth (%d) reached, "
                     "cannot parse further.\n", EBML_MAX_DEPTH);
              ret = AVERROR_INVALIDDATA;
          } else {
              level.start = 0;
              level.length = (uint64_t)-1;
              matroska->levels[matroska->num_levels] = level;
              matroska->num_levels++;
              matroska->current_id = 0;
  
              ret = ebml_parse(matroska, matroska_segment, matroska);
  
              /* remove dummy level */
              while (matroska->num_levels) {
                  uint64_t length = matroska->levels[--matroska->num_levels].length;
                  if (length == (uint64_t)-1)
                      break;
              }
          }
      }
      /* seek back */
      avio_seek(matroska->ctx->pb, before_pos, SEEK_SET);
      matroska->level_up = level_up;
      matroska->current_id = saved_id;
  
      return ret;
  }
  
  static void matroska_execute_seekhead(MatroskaDemuxContext *matroska)
  {
      EbmlList *seekhead_list = &matroska->seekhead;
      int64_t before_pos = avio_tell(matroska->ctx->pb);
      int i;
  
      // we should not do any seeking in the streaming case
      if (!matroska->ctx->pb->seekable ||
          (matroska->ctx->flags & AVFMT_FLAG_IGNIDX))
          return;
  
      for (i = 0; i < seekhead_list->nb_elem; i++) {
          MatroskaSeekhead *seekhead = seekhead_list->elem;
          if (seekhead[i].pos <= before_pos)
              continue;
  
          // defer cues parsing until we actually need cue data.
          if (seekhead[i].id == MATROSKA_ID_CUES) {
              matroska->cues_parsing_deferred = 1;
              continue;
          }
  
          if (matroska_parse_seekhead_entry(matroska, i) < 0)
              break;
      }
  }
  
  static void matroska_add_index_entries(MatroskaDemuxContext *matroska) {
      EbmlList *index_list;
      MatroskaIndex *index;
      int index_scale = 1;
      int i, j;
  
      index_list = &matroska->index;
      index = index_list->elem;
      if (index_list->nb_elem
          && index[0].time > 1E14/matroska->time_scale) {
          av_log(matroska->ctx, AV_LOG_WARNING, "Working around broken index.\n");
          index_scale = matroska->time_scale;
      }
      for (i = 0; i < index_list->nb_elem; i++) {
          EbmlList *pos_list = &index[i].pos;
          MatroskaIndexPos *pos = pos_list->elem;
          for (j = 0; j < pos_list->nb_elem; j++) {
              MatroskaTrack *track = matroska_find_track_by_num(matroska, pos[j].track);
              if (track && track->stream)
                  av_add_index_entry(track->stream,
                                     pos[j].pos + matroska->segment_start,
                                     index[i].time/index_scale, 0, 0,
                                     AVINDEX_KEYFRAME);
          }
      }
  }
  
  static void matroska_parse_cues(MatroskaDemuxContext *matroska) {
      EbmlList *seekhead_list = &matroska->seekhead;
      MatroskaSeekhead *seekhead = seekhead_list->elem;
      int i;
  
      for (i = 0; i < seekhead_list->nb_elem; i++)
          if (seekhead[i].id == MATROSKA_ID_CUES)
              break;
      assert(i <= seekhead_list->nb_elem);
  
      matroska_parse_seekhead_entry(matroska, i);
      matroska_add_index_entries(matroska);
  }
  
  static int matroska_aac_profile(char *codec_id)
  {
      static const char * const aac_profiles[] = { "MAIN", "LC", "SSR" };
      int profile;
  
      for (profile=0; profile<FF_ARRAY_ELEMS(aac_profiles); profile++)
          if (strstr(codec_id, aac_profiles[profile]))
              break;
      return profile + 1;
  }
  
  static int matroska_aac_sri(int samplerate)
  {
      int sri;
  
      for (sri=0; sri<FF_ARRAY_ELEMS(avpriv_mpeg4audio_sample_rates); sri++)
          if (avpriv_mpeg4audio_sample_rates[sri] == samplerate)
              break;
      return sri;
  }
  
  static int matroska_read_header(AVFormatContext *s, AVFormatParameters *ap)
  {
      MatroskaDemuxContext *matroska = s->priv_data;
      EbmlList *attachements_list = &matroska->attachments;
      MatroskaAttachement *attachements;
      EbmlList *chapters_list = &matroska->chapters;
      MatroskaChapter *chapters;
      MatroskaTrack *tracks;
      uint64_t max_start = 0;
      Ebml ebml = { 0 };
      AVStream *st;
      int i, j, k, res;
  
      matroska->ctx = s;
  
      /* First read the EBML header. */
      if (ebml_parse(matroska, ebml_syntax, &ebml)
          || ebml.version > EBML_VERSION       || ebml.max_size > sizeof(uint64_t)
          || ebml.id_length > sizeof(uint32_t) || ebml.doctype_version > 3) {
          av_log(matroska->ctx, AV_LOG_ERROR,
                 "EBML header using unsupported features\n"
                 "(EBML version %"PRIu64", doctype %s, doc version %"PRIu64")\n",
                 ebml.version, ebml.doctype, ebml.doctype_version);
          ebml_free(ebml_syntax, &ebml);
          return AVERROR_PATCHWELCOME;
      } else if (ebml.doctype_version == 3) {
          av_log(matroska->ctx, AV_LOG_WARNING,
                 "EBML header using unsupported features\n"
                 "(EBML version %"PRIu64", doctype %s, doc version %"PRIu64")\n",
                 ebml.version, ebml.doctype, ebml.doctype_version);
      }
      for (i = 0; i < FF_ARRAY_ELEMS(matroska_doctypes); i++)
          if (!strcmp(ebml.doctype, matroska_doctypes[i]))
              break;
      if (i >= FF_ARRAY_ELEMS(matroska_doctypes)) {
          av_log(s, AV_LOG_WARNING, "Unknown EBML doctype '%s'\n", ebml.doctype);
      }
      ebml_free(ebml_syntax, &ebml);
  
      /* The next thing is a segment. */
      if ((res = ebml_parse(matroska, matroska_segments, matroska)) < 0)
          return res;
      matroska_execute_seekhead(matroska);
  
      if (!matroska->time_scale)
          matroska->time_scale = 1000000;
      if (matroska->duration)
          matroska->ctx->duration = matroska->duration * matroska->time_scale
                                    * 1000 / AV_TIME_BASE;
      av_dict_set(&s->metadata, "title", matroska->title, 0);
  
      tracks = matroska->tracks.elem;
      for (i=0; i < matroska->tracks.nb_elem; i++) {
          MatroskaTrack *track = &tracks[i];
          enum CodecID codec_id = CODEC_ID_NONE;
          EbmlList *encodings_list = &track->encodings;
          MatroskaTrackEncoding *encodings = encodings_list->elem;
          uint8_t *extradata = NULL;
          int extradata_size = 0;
          int extradata_offset = 0;
          uint32_t fourcc = 0;
          AVIOContext b;
  
          /* Apply some sanity checks. */
          if (track->type != MATROSKA_TRACK_TYPE_VIDEO &&
              track->type != MATROSKA_TRACK_TYPE_AUDIO &&
              track->type != MATROSKA_TRACK_TYPE_SUBTITLE) {
              av_log(matroska->ctx, AV_LOG_INFO,
                     "Unknown or unsupported track type %"PRIu64"\n",
                     track->type);
              continue;
          }
          if (track->codec_id == NULL)
              continue;
  
          if (track->type == MATROSKA_TRACK_TYPE_VIDEO) {
              if (!track->default_duration)
                  track->default_duration = 1000000000/track->video.frame_rate;
              if (!track->video.display_width)
                  track->video.display_width = track->video.pixel_width;
              if (!track->video.display_height)
                  track->video.display_height = track->video.pixel_height;
              if (track->video.color_space.size == 4)
                  fourcc = AV_RL32(track->video.color_space.data);
          } else if (track->type == MATROSKA_TRACK_TYPE_AUDIO) {
              if (!track->audio.out_samplerate)
                  track->audio.out_samplerate = track->audio.samplerate;
          }
          if (encodings_list->nb_elem > 1) {
              av_log(matroska->ctx, AV_LOG_ERROR,
                     "Multiple combined encodings not supported");
          } else if (encodings_list->nb_elem == 1) {
              if (encodings[0].type ||
                  (encodings[0].compression.algo != MATROSKA_TRACK_ENCODING_COMP_HEADERSTRIP &&
  #if CONFIG_ZLIB
                   encodings[0].compression.algo != MATROSKA_TRACK_ENCODING_COMP_ZLIB &&
  #endif
  #if CONFIG_BZLIB
                   encodings[0].compression.algo != MATROSKA_TRACK_ENCODING_COMP_BZLIB &&
  #endif
                   encodings[0].compression.algo != MATROSKA_TRACK_ENCODING_COMP_LZO)) {
                  encodings[0].scope = 0;
                  av_log(matroska->ctx, AV_LOG_ERROR,
                         "Unsupported encoding type");
              } else if (track->codec_priv.size && encodings[0].scope&2) {
                  uint8_t *codec_priv = track->codec_priv.data;
                  int offset = matroska_decode_buffer(&track->codec_priv.data,
                                                      &track->codec_priv.size,
                                                      track);
                  if (offset < 0) {
                      track->codec_priv.data = NULL;
                      track->codec_priv.size = 0;
                      av_log(matroska->ctx, AV_LOG_ERROR,
                             "Failed to decode codec private data\n");
                  } else if (offset > 0) {
                      track->codec_priv.data = av_malloc(track->codec_priv.size + offset);
                      memcpy(track->codec_priv.data,
                             encodings[0].compression.settings.data, offset);
                      memcpy(track->codec_priv.data+offset, codec_priv,
                             track->codec_priv.size);
                      track->codec_priv.size += offset;
                  }
                  if (codec_priv != track->codec_priv.data)
                      av_free(codec_priv);
              }
          }
  
          for(j=0; ff_mkv_codec_tags[j].id != CODEC_ID_NONE; j++){
              if(!strncmp(ff_mkv_codec_tags[j].str, track->codec_id,
                          strlen(ff_mkv_codec_tags[j].str))){
                  codec_id= ff_mkv_codec_tags[j].id;
                  break;
              }
          }
  
          st = track->stream = avformat_new_stream(s, NULL);
          if (st == NULL)
              return AVERROR(ENOMEM);
  
          if (!strcmp(track->codec_id, "V_MS/VFW/FOURCC")
              && track->codec_priv.size >= 40
              && track->codec_priv.data != NULL) {
              track->ms_compat = 1;
              fourcc = AV_RL32(track->codec_priv.data + 16);
              codec_id = ff_codec_get_id(ff_codec_bmp_tags, fourcc);
              extradata_offset = 40;
          } else if (!strcmp(track->codec_id, "A_MS/ACM")
                     && track->codec_priv.size >= 14
                     && track->codec_priv.data != NULL) {
              int ret;
              ffio_init_context(&b, track->codec_priv.data, track->codec_priv.size,
                            AVIO_FLAG_READ, NULL, NULL, NULL, NULL);
              ret = ff_get_wav_header(&b, st->codec, track->codec_priv.size);
              if (ret < 0)
                  return ret;
              codec_id = st->codec->codec_id;
              extradata_offset = FFMIN(track->codec_priv.size, 18);
          } else if (!strcmp(track->codec_id, "V_QUICKTIME")
                     && (track->codec_priv.size >= 86)
                     && (track->codec_priv.data != NULL)) {
              fourcc = AV_RL32(track->codec_priv.data);
              codec_id = ff_codec_get_id(codec_movvideo_tags, fourcc);
          } else if (codec_id == CODEC_ID_PCM_S16BE) {
              switch (track->audio.bitdepth) {
              case  8:  codec_id = CODEC_ID_PCM_U8;     break;
              case 24:  codec_id = CODEC_ID_PCM_S24BE;  break;
              case 32:  codec_id = CODEC_ID_PCM_S32BE;  break;
              }
          } else if (codec_id == CODEC_ID_PCM_S16LE) {
              switch (track->audio.bitdepth) {
              case  8:  codec_id = CODEC_ID_PCM_U8;     break;
              case 24:  codec_id = CODEC_ID_PCM_S24LE;  break;
              case 32:  codec_id = CODEC_ID_PCM_S32LE;  break;
              }
          } else if (codec_id==CODEC_ID_PCM_F32LE && track->audio.bitdepth==64) {
              codec_id = CODEC_ID_PCM_F64LE;
          } else if (codec_id == CODEC_ID_AAC && !track->codec_priv.size) {
              int profile = matroska_aac_profile(track->codec_id);
              int sri = matroska_aac_sri(track->audio.samplerate);
              extradata = av_mallocz(5 + FF_INPUT_BUFFER_PADDING_SIZE);
              if (extradata == NULL)
                  return AVERROR(ENOMEM);
              extradata[0] = (profile << 3) | ((sri&0x0E) >> 1);
              extradata[1] = ((sri&0x01) << 7) | (track->audio.channels<<3);
              if (strstr(track->codec_id, "SBR")) {
                  sri = matroska_aac_sri(track->audio.out_samplerate);
                  extradata[2] = 0x56;
                  extradata[3] = 0xE5;
                  extradata[4] = 0x80 | (sri<<3);
                  extradata_size = 5;
              } else
                  extradata_size = 2;
          } else if (codec_id == CODEC_ID_TTA) {
              extradata_size = 30;
              extradata = av_mallocz(extradata_size + FF_INPUT_BUFFER_PADDING_SIZE);
              if (extradata == NULL)
                  return AVERROR(ENOMEM);
              ffio_init_context(&b, extradata, extradata_size, 1,
                            NULL, NULL, NULL, NULL);
              avio_write(&b, "TTA1", 4);
              avio_wl16(&b, 1);
              avio_wl16(&b, track->audio.channels);
              avio_wl16(&b, track->audio.bitdepth);
              avio_wl32(&b, track->audio.out_samplerate);
              avio_wl32(&b, matroska->ctx->duration * track->audio.out_samplerate);
          } else if (codec_id == CODEC_ID_RV10 || codec_id == CODEC_ID_RV20 ||
                     codec_id == CODEC_ID_RV30 || codec_id == CODEC_ID_RV40) {
              extradata_offset = 26;
          } else if (codec_id == CODEC_ID_RA_144) {
              track->audio.out_samplerate = 8000;
              track->audio.channels = 1;
          } else if (codec_id == CODEC_ID_RA_288 || codec_id == CODEC_ID_COOK ||
                     codec_id == CODEC_ID_ATRAC3 || codec_id == CODEC_ID_SIPR) {
              int flavor;
              ffio_init_context(&b, track->codec_priv.data,track->codec_priv.size,
                            0, NULL, NULL, NULL, NULL);
              avio_skip(&b, 22);
              flavor                       = avio_rb16(&b);
              track->audio.coded_framesize = avio_rb32(&b);
              avio_skip(&b, 12);
              track->audio.sub_packet_h    = avio_rb16(&b);
              track->audio.frame_size      = avio_rb16(&b);
              track->audio.sub_packet_size = avio_rb16(&b);
              track->audio.buf = av_malloc(track->audio.frame_size * track->audio.sub_packet_h);
              if (codec_id == CODEC_ID_RA_288) {
                  st->codec->block_align = track->audio.coded_framesize;
                  track->codec_priv.size = 0;
              } else {
                  if (codec_id == CODEC_ID_SIPR && flavor < 4) {
                      const int sipr_bit_rate[4] = { 6504, 8496, 5000, 16000 };
                      track->audio.sub_packet_size = ff_sipr_subpk_size[flavor];
                      st->codec->bit_rate = sipr_bit_rate[flavor];
                  }
                  st->codec->block_align = track->audio.sub_packet_size;
                  extradata_offset = 78;
              }
          }
          track->codec_priv.size -= extradata_offset;
  
          if (codec_id == CODEC_ID_NONE)
              av_log(matroska->ctx, AV_LOG_INFO,
                     "Unknown/unsupported CodecID %s.\n", track->codec_id);
  
          if (track->time_scale < 0.01)
              track->time_scale = 1.0;
          avpriv_set_pts_info(st, 64, matroska->time_scale*track->time_scale, 1000*1000*1000); /* 64 bit pts in ns */
  
          st->codec->codec_id = codec_id;
          st->start_time = 0;
          if (strcmp(track->language, "und"))
              av_dict_set(&st->metadata, "language", track->language, 0);
          av_dict_set(&st->metadata, "title", track->name, 0);
  
          if (track->flag_default)
              st->disposition |= AV_DISPOSITION_DEFAULT;
          if (track->flag_forced)
              st->disposition |= AV_DISPOSITION_FORCED;
  
          if (!st->codec->extradata) {
              if(extradata){
                  st->codec->extradata = extradata;
                  st->codec->extradata_size = extradata_size;
              } else if(track->codec_priv.data && track->codec_priv.size > 0){
                  st->codec->extradata = av_mallocz(track->codec_priv.size +
                                                    FF_INPUT_BUFFER_PADDING_SIZE);
                  if(st->codec->extradata == NULL)
                      return AVERROR(ENOMEM);
                  st->codec->extradata_size = track->codec_priv.size;
                  memcpy(st->codec->extradata,
                         track->codec_priv.data + extradata_offset,
                         track->codec_priv.size);
              }
          }
  
          if (track->type == MATROSKA_TRACK_TYPE_VIDEO) {
              MatroskaTrackPlane *planes = track->operation.combine_planes.elem;
  
              st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
              st->codec->codec_tag  = fourcc;
              st->codec->width  = track->video.pixel_width;
              st->codec->height = track->video.pixel_height;
              av_reduce(&st->sample_aspect_ratio.num,
                        &st->sample_aspect_ratio.den,
                        st->codec->height * track->video.display_width,
                        st->codec-> width * track->video.display_height,
                        255);
              if (st->codec->codec_id != CODEC_ID_H264)
              st->need_parsing = AVSTREAM_PARSE_HEADERS;
              if (track->default_duration)
                  st->avg_frame_rate = av_d2q(1000000000.0/track->default_duration, INT_MAX);
  
              /* export stereo mode flag as metadata tag */
              if (track->video.stereo_mode && track->video.stereo_mode < MATROSKA_VIDEO_STEREO_MODE_COUNT)
                  av_dict_set(&st->metadata, "stereo_mode", matroska_video_stereo_mode[track->video.stereo_mode], 0);
  
              /* if we have virtual track, mark the real tracks */
              for (j=0; j < track->operation.combine_planes.nb_elem; j++) {
                  char buf[32];
                  if (planes[j].type >= MATROSKA_VIDEO_STEREO_PLANE_COUNT)
                      continue;
                  snprintf(buf, sizeof(buf), "%s_%d",
                           matroska_video_stereo_plane[planes[j].type], i);
                  for (k=0; k < matroska->tracks.nb_elem; k++)
                      if (planes[j].uid == tracks[k].uid) {
                          av_dict_set(&s->streams[k]->metadata,
                                      "stereo_mode", buf, 0);
                          break;
                      }
              }
          } else if (track->type == MATROSKA_TRACK_TYPE_AUDIO) {
              st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
              st->codec->sample_rate = track->audio.out_samplerate;
              st->codec->channels = track->audio.channels;
              if (st->codec->codec_id != CODEC_ID_AAC)
              st->need_parsing = AVSTREAM_PARSE_HEADERS;
          } else if (track->type == MATROSKA_TRACK_TYPE_SUBTITLE) {
              st->codec->codec_type = AVMEDIA_TYPE_SUBTITLE;
          }
      }
  
      attachements = attachements_list->elem;
      for (j=0; j<attachements_list->nb_elem; j++) {
          if (!(attachements[j].filename && attachements[j].mime &&
                attachements[j].bin.data && attachements[j].bin.size > 0)) {
              av_log(matroska->ctx, AV_LOG_ERROR, "incomplete attachment\n");
          } else {
              AVStream *st = avformat_new_stream(s, NULL);
              if (st == NULL)
                  break;
              av_dict_set(&st->metadata, "filename",attachements[j].filename, 0);
              av_dict_set(&st->metadata, "mimetype", attachements[j].mime, 0);
              st->codec->codec_id = CODEC_ID_NONE;
              st->codec->codec_type = AVMEDIA_TYPE_ATTACHMENT;
              st->codec->extradata  = av_malloc(attachements[j].bin.size + FF_INPUT_BUFFER_PADDING_SIZE);
              if(st->codec->extradata == NULL)
                  break;
              st->codec->extradata_size = attachements[j].bin.size;
              memcpy(st->codec->extradata, attachements[j].bin.data, attachements[j].bin.size);
  
              for (i=0; ff_mkv_mime_tags[i].id != CODEC_ID_NONE; i++) {
                  if (!strncmp(ff_mkv_mime_tags[i].str, attachements[j].mime,
                               strlen(ff_mkv_mime_tags[i].str))) {
                      st->codec->codec_id = ff_mkv_mime_tags[i].id;
                      break;
                  }
              }
              attachements[j].stream = st;
          }
      }
  
      chapters = chapters_list->elem;
      for (i=0; i<chapters_list->nb_elem; i++)
          if (chapters[i].start != AV_NOPTS_VALUE && chapters[i].uid
              && (max_start==0 || chapters[i].start > max_start)) {
              chapters[i].chapter =
              avpriv_new_chapter(s, chapters[i].uid, (AVRational){1, 1000000000},
                             chapters[i].start, chapters[i].end,
                             chapters[i].title);
              av_dict_set(&chapters[i].chapter->metadata,
                               "title", chapters[i].title, 0);
              max_start = chapters[i].start;
          }
  
      matroska_add_index_entries(matroska);
  
      matroska_convert_tags(s);
  
      return 0;
  }
  
  /*
   * Put one packet in an application-supplied AVPacket struct.
   * Returns 0 on success or -1 on failure.
   */
  static int matroska_deliver_packet(MatroskaDemuxContext *matroska,
                                     AVPacket *pkt)
  {
      if (matroska->num_packets > 0) {
          memcpy(pkt, matroska->packets[0], sizeof(AVPacket));
          av_free(matroska->packets[0]);
          if (matroska->num_packets > 1) {
              void *newpackets;
              memmove(&matroska->packets[0], &matroska->packets[1],
                      (matroska->num_packets - 1) * sizeof(AVPacket *));
              newpackets = av_realloc(matroska->packets,
                              (matroska->num_packets - 1) * sizeof(AVPacket *));
              if (newpackets)
                  matroska->packets = newpackets;
          } else {
              av_freep(&matroska->packets);
          }
          matroska->num_packets--;
          return 0;
      }
  
      return -1;
  }
  
  /*
   * Free all packets in our internal queue.
   */
  static void matroska_clear_queue(MatroskaDemuxContext *matroska)
  {
      if (matroska->packets) {
          int n;
          for (n = 0; n < matroska->num_packets; n++) {
              av_free_packet(matroska->packets[n]);
              av_free(matroska->packets[n]);
          }
          av_freep(&matroska->packets);
          matroska->num_packets = 0;
      }
  }
  
  static int matroska_parse_block(MatroskaDemuxContext *matroska, uint8_t *data,
                                  int size, int64_t pos, uint64_t cluster_time,
                                  uint64_t duration, int is_keyframe,
                                  int64_t cluster_pos)
  {
      uint64_t timecode = AV_NOPTS_VALUE;
      MatroskaTrack *track;
      int res = 0;
      AVStream *st;
      AVPacket *pkt;
      int16_t block_time;
      uint32_t *lace_size = NULL;
      int n, flags, laces = 0;
      uint64_t num;
  
      if ((n = matroska_ebmlnum_uint(matroska, data, size, &num)) < 0) {
          av_log(matroska->ctx, AV_LOG_ERROR, "EBML block data error\n");
          return res;
      }
      data += n;
      size -= n;
  
      track = matroska_find_track_by_num(matroska, num);
      if (!track || !track->stream) {
          av_log(matroska->ctx, AV_LOG_INFO,
                 "Invalid stream %"PRIu64" or size %u\n", num, size);
          return res;
      } else if (size <= 3)
          return 0;
      st = track->stream;
      if (st->discard >= AVDISCARD_ALL)
          return res;
      if (!duration)
          duration = track->default_duration / matroska->time_scale;
  
      block_time = AV_RB16(data);
      data += 2;
      flags = *data++;
      size -= 3;
      if (is_keyframe == -1)
          is_keyframe = flags & 0x80 ? AV_PKT_FLAG_KEY : 0;
  
      if (cluster_time != (uint64_t)-1
          && (block_time >= 0 || cluster_time >= -block_time)) {
          timecode = cluster_time + block_time;
          if (track->type == MATROSKA_TRACK_TYPE_SUBTITLE
              && timecode < track->end_timecode)
              is_keyframe = 0;  /* overlapping subtitles are not key frame */
          if (is_keyframe)
              av_add_index_entry(st, cluster_pos, timecode, 0,0,AVINDEX_KEYFRAME);
          track->end_timecode = FFMAX(track->end_timecode, timecode+duration);
      }
  
      if (matroska->skip_to_keyframe && track->type != MATROSKA_TRACK_TYPE_SUBTITLE) {
          if (!is_keyframe || timecode < matroska->skip_to_timecode)
              return res;
          matroska->skip_to_keyframe = 0;
      }
  
      switch ((flags & 0x06) >> 1) {
          case 0x0: /* no lacing */
              laces = 1;
              lace_size = av_mallocz(sizeof(int));
              lace_size[0] = size;
              break;
  
          case 0x1: /* Xiph lacing */
          case 0x2: /* fixed-size lacing */
          case 0x3: /* EBML lacing */
              assert(size>0); // size <=3 is checked before size-=3 above
              laces = (*data) + 1;
              data += 1;
              size -= 1;
              lace_size = av_mallocz(laces * sizeof(int));
  
              switch ((flags & 0x06) >> 1) {
                  case 0x1: /* Xiph lacing */ {
                      uint8_t temp;
                      uint32_t total = 0;
                      for (n = 0; res == 0 && n < laces - 1; n++) {
                          while (1) {
                              if (size == 0) {
                                  res = -1;
                                  break;
                              }
                              temp = *data;
                              lace_size[n] += temp;
                              data += 1;
                              size -= 1;
                              if (temp != 0xff)
                                  break;
                          }
                          total += lace_size[n];
                      }
                      lace_size[n] = size - total;
                      break;
                  }
  
                  case 0x2: /* fixed-size lacing */
                      for (n = 0; n < laces; n++)
                          lace_size[n] = size / laces;
                      break;
  
                  case 0x3: /* EBML lacing */ {
                      uint32_t total;
                      n = matroska_ebmlnum_uint(matroska, data, size, &num);
                      if (n < 0) {
                          av_log(matroska->ctx, AV_LOG_INFO,
                                 "EBML block data error\n");
                          break;
                      }
                      data += n;
                      size -= n;
                      total = lace_size[0] = num;
                      for (n = 1; res == 0 && n < laces - 1; n++) {
                          int64_t snum;
                          int r;
                          r = matroska_ebmlnum_sint(matroska, data, size, &snum);
                          if (r < 0) {
                              av_log(matroska->ctx, AV_LOG_INFO,
                                     "EBML block data error\n");
                              break;
                          }
                          data += r;
                          size -= r;
                          lace_size[n] = lace_size[n - 1] + snum;
                          total += lace_size[n];
                      }
                      lace_size[laces - 1] = size - total;
                      break;
                  }
              }
              break;
      }
  
      if (res == 0) {
          for (n = 0; n < laces; n++) {
              if ((st->codec->codec_id == CODEC_ID_RA_288 ||
                   st->codec->codec_id == CODEC_ID_COOK ||
                   st->codec->codec_id == CODEC_ID_SIPR ||
                   st->codec->codec_id == CODEC_ID_ATRAC3) &&
                   st->codec->block_align && track->audio.sub_packet_size) {
                  int a = st->codec->block_align;
                  int sps = track->audio.sub_packet_size;
                  int cfs = track->audio.coded_framesize;
                  int h = track->audio.sub_packet_h;
                  int y = track->audio.sub_packet_cnt;
                  int w = track->audio.frame_size;
                  int x;
  
                  if (!track->audio.pkt_cnt) {
                      if (track->audio.sub_packet_cnt == 0)
                          track->audio.buf_timecode = timecode;
                      if (st->codec->codec_id == CODEC_ID_RA_288)
                          for (x=0; x<h/2; x++)
                              memcpy(track->audio.buf+x*2*w+y*cfs,
                                     data+x*cfs, cfs);
                      else if (st->codec->codec_id == CODEC_ID_SIPR)
                          memcpy(track->audio.buf + y*w, data, w);
                      else
                          for (x=0; x<w/sps; x++)
                              memcpy(track->audio.buf+sps*(h*x+((h+1)/2)*(y&1)+(y>>1)), data+x*sps, sps);
  
                      if (++track->audio.sub_packet_cnt >= h) {
                          if (st->codec->codec_id == CODEC_ID_SIPR)
                              ff_rm_reorder_sipr_data(track->audio.buf, h, w);
                          track->audio.sub_packet_cnt = 0;
                          track->audio.pkt_cnt = h*w / a;
                      }
                  }
                  while (track->audio.pkt_cnt) {
                      pkt = av_mallocz(sizeof(AVPacket));
                      av_new_packet(pkt, a);
                      memcpy(pkt->data, track->audio.buf
                             + a * (h*w / a - track->audio.pkt_cnt--), a);
                      pkt->pts = track->audio.buf_timecode;
                      track->audio.buf_timecode = AV_NOPTS_VALUE;
                      pkt->pos = pos;
                      pkt->stream_index = st->index;
                      dynarray_add(&matroska->packets,&matroska->num_packets,pkt);
                  }
              } else {
                  MatroskaTrackEncoding *encodings = track->encodings.elem;
                  int offset = 0, pkt_size = lace_size[n];
                  uint8_t *pkt_data = data;
  
                  if (pkt_size > size) {
                      av_log(matroska->ctx, AV_LOG_ERROR, "Invalid packet size\n");
                      break;
                  }
  
                  if (encodings && encodings->scope & 1) {
                      offset = matroska_decode_buffer(&pkt_data,&pkt_size, track);
                      if (offset < 0)
                          continue;
                  }
  
                  pkt = av_mallocz(sizeof(AVPacket));
                  /* XXX: prevent data copy... */
                  if (av_new_packet(pkt, pkt_size+offset) < 0) {
                      av_free(pkt);
                      res = AVERROR(ENOMEM);
                      break;
                  }
                  if (offset)
                      memcpy (pkt->data, encodings->compression.settings.data, offset);
                  memcpy (pkt->data+offset, pkt_data, pkt_size);
  
                  if (pkt_data != data)
                      av_free(pkt_data);
  
                  if (n == 0)
                      pkt->flags = is_keyframe;
                  pkt->stream_index = st->index;
  
                  if (track->ms_compat)
                      pkt->dts = timecode;
                  else
                      pkt->pts = timecode;
                  pkt->pos = pos;
                  if (st->codec->codec_id == CODEC_ID_TEXT)
                      pkt->convergence_duration = duration;
                  else if (track->type != MATROSKA_TRACK_TYPE_SUBTITLE)
                      pkt->duration = duration;
  
                  if (st->codec->codec_id == CODEC_ID_SSA)
                      matroska_fix_ass_packet(matroska, pkt, duration);
  
                  if (matroska->prev_pkt &&
                      timecode != AV_NOPTS_VALUE &&
                      matroska->prev_pkt->pts == timecode &&
                      matroska->prev_pkt->stream_index == st->index &&
                      st->codec->codec_id == CODEC_ID_SSA)
                      matroska_merge_packets(matroska->prev_pkt, pkt);
                  else {
                      dynarray_add(&matroska->packets,&matroska->num_packets,pkt);
                      matroska->prev_pkt = pkt;
                  }
              }
  
              if (timecode != AV_NOPTS_VALUE)
                  timecode = duration ? timecode + duration : AV_NOPTS_VALUE;
              data += lace_size[n];
              size -= lace_size[n];
          }
      }
  
      av_free(lace_size);
      return res;
  }
  
  static int matroska_parse_cluster(MatroskaDemuxContext *matroska)
  {
      MatroskaCluster cluster = { 0 };
      EbmlList *blocks_list;
      MatroskaBlock *blocks;
      int i, res;
      int64_t pos = avio_tell(matroska->ctx->pb);
      matroska->prev_pkt = NULL;
      if (matroska->current_id)
          pos -= 4;  /* sizeof the ID which was already read */
      res = ebml_parse(matroska, matroska_clusters, &cluster);
      blocks_list = &cluster.blocks;
      blocks = blocks_list->elem;
      for (i=0; i<blocks_list->nb_elem; i++)
          if (blocks[i].bin.size > 0 && blocks[i].bin.data) {
              int is_keyframe = blocks[i].non_simple ? !blocks[i].reference : -1;
              res=matroska_parse_block(matroska,
                                       blocks[i].bin.data, blocks[i].bin.size,
                                       blocks[i].bin.pos,  cluster.timecode,
                                       blocks[i].duration, is_keyframe,
                                       pos);
          }
      ebml_free(matroska_cluster, &cluster);
      if (res < 0)  matroska->done = 1;
      return res;
  }
  
  static int matroska_read_packet(AVFormatContext *s, AVPacket *pkt)
  {
      MatroskaDemuxContext *matroska = s->priv_data;
  
      while (matroska_deliver_packet(matroska, pkt)) {
          if (matroska->done)
              return AVERROR_EOF;
          matroska_parse_cluster(matroska);
      }
  
      return 0;
  }
  
  static int matroska_read_seek(AVFormatContext *s, int stream_index,
                                int64_t timestamp, int flags)
  {
      MatroskaDemuxContext *matroska = s->priv_data;
      MatroskaTrack *tracks = matroska->tracks.elem;
      AVStream *st = s->streams[stream_index];
      int i, index, index_sub, index_min;
  
      /* Parse the CUES now since we need the index data to seek. */
      if (matroska->cues_parsing_deferred) {
          matroska_parse_cues(matroska);
          matroska->cues_parsing_deferred = 0;
      }
  
      if (!st->nb_index_entries)
          return 0;
      timestamp = FFMAX(timestamp, st->index_entries[0].timestamp);
  
      if ((index = av_index_search_timestamp(st, timestamp, flags)) < 0) {
          avio_seek(s->pb, st->index_entries[st->nb_index_entries-1].pos, SEEK_SET);
          matroska->current_id = 0;
          while ((index = av_index_search_timestamp(st, timestamp, flags)) < 0) {
              matroska_clear_queue(matroska);
              if (matroska_parse_cluster(matroska) < 0)
                  break;
          }
      }
  
      matroska_clear_queue(matroska);
      if (index < 0)
          return 0;
  
      index_min = index;
      for (i=0; i < matroska->tracks.nb_elem; i++) {
          tracks[i].audio.pkt_cnt = 0;
          tracks[i].audio.sub_packet_cnt = 0;
          tracks[i].audio.buf_timecode = AV_NOPTS_VALUE;
          tracks[i].end_timecode = 0;
          if (tracks[i].type == MATROSKA_TRACK_TYPE_SUBTITLE
              && !tracks[i].stream->discard != AVDISCARD_ALL) {
              index_sub = av_index_search_timestamp(tracks[i].stream, st->index_entries[index].timestamp, AVSEEK_FLAG_BACKWARD);
              if (index_sub >= 0
                  && st->index_entries[index_sub].pos < st->index_entries[index_min].pos
                  && st->index_entries[index].timestamp - st->index_entries[index_sub].timestamp < 30000000000/matroska->time_scale)
                  index_min = index_sub;
          }
      }
  
      avio_seek(s->pb, st->index_entries[index_min].pos, SEEK_SET);
      matroska->current_id = 0;
      matroska->skip_to_keyframe = !(flags & AVSEEK_FLAG_ANY);
      matroska->skip_to_timecode = st->index_entries[index].timestamp;
      matroska->done = 0;
      ff_update_cur_dts(s, st, st->index_entries[index].timestamp);
      return 0;
  }
  
  static int matroska_read_close(AVFormatContext *s)
  {
      MatroskaDemuxContext *matroska = s->priv_data;
      MatroskaTrack *tracks = matroska->tracks.elem;
      int n;
  
      matroska_clear_queue(matroska);
  
      for (n=0; n < matroska->tracks.nb_elem; n++)
          if (tracks[n].type == MATROSKA_TRACK_TYPE_AUDIO)
              av_free(tracks[n].audio.buf);
      ebml_free(matroska_segment, matroska);
  
      return 0;
  }
  
  AVInputFormat ff_matroska_demuxer = {
      .name           = "matroska,webm",
      .long_name      = NULL_IF_CONFIG_SMALL("Matroska/WebM file format"),
      .priv_data_size = sizeof(MatroskaDemuxContext),
      .read_probe     = matroska_probe,
      .read_header    = matroska_read_header,
      .read_packet    = matroska_read_packet,
      .read_close     = matroska_read_close,
      .read_seek      = matroska_read_seek,
  };
  