text: /*
   * FLAC parser
   * Copyright (c) 2010 Michael Chinen
   *
   * 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
   * FLAC parser
   *
   * The FLAC parser buffers input until FLAC_MIN_HEADERS has been found.
   * Each time it finds and verifies a CRC-8 header it sees which of the
   * FLAC_MAX_SEQUENTIAL_HEADERS that came before it have a valid CRC-16 footer
   * that ends at the newly found header.
   * Headers are scored by FLAC_HEADER_BASE_SCORE plus the max of its crc-verified
   * children, penalized by changes in sample rate, frame number, etc.
   * The parser returns the frame with the highest score.
   **/
  
  #include "libavutil/attributes.h"
  #include "libavutil/crc.h"
  #include "bytestream.h"
  #include "parser.h"
  #include "flac.h"
  
  /** maximum number of adjacent headers that compare CRCs against each other   */
  #define FLAC_MAX_SEQUENTIAL_HEADERS 4
  /** minimum number of headers buffered and checked before returning frames    */
  #define FLAC_MIN_HEADERS 10
  /** estimate for average size of a FLAC frame                                 */
  #define FLAC_AVG_FRAME_SIZE 8192
  
  /** scoring settings for score_header */
  #define FLAC_HEADER_BASE_SCORE        10
  #define FLAC_HEADER_CHANGED_PENALTY   7
  #define FLAC_HEADER_CRC_FAIL_PENALTY  50
  #define FLAC_HEADER_NOT_PENALIZED_YET 100000
  #define FLAC_HEADER_NOT_SCORED_YET    -100000
  
  /** largest possible size of flac header */
  #define MAX_FRAME_HEADER_SIZE 16
  #define MAX_FRAME_VERIFY_SIZE (MAX_FRAME_HEADER_SIZE + 1)
  
  typedef struct FifoBuffer {
      uint8_t *buffer;
      uint8_t *end;
      uint8_t *rptr;
      uint8_t *wptr;
      int empty;
  } FifoBuffer;
  
  typedef struct FLACHeaderMarker {
      int offset;       /**< byte offset from start of FLACParseContext->buffer */
      int link_penalty[FLAC_MAX_SEQUENTIAL_HEADERS]; /**< array of local scores
                             between this header and the one at a distance equal
                             array position                                     */
      int max_score;    /**< maximum score found after checking each child that
                             has a valid CRC                                    */
      FLACFrameInfo fi; /**< decoded frame header info                          */
      struct FLACHeaderMarker *next;       /**< next CRC-8 verified header that
                                                immediately follows this one in
                                                the bytestream                  */
      struct FLACHeaderMarker *best_child; /**< following frame header with
                                                which this frame has the best
                                                score with                      */
  } FLACHeaderMarker;
  
  typedef struct FLACParseContext {
      AVCodecParserContext *pc;      /**< parent context                        */
      AVCodecContext *avctx;         /**< codec context pointer for logging     */
      FLACHeaderMarker *headers;     /**< linked-list that starts at the first
                                          CRC-8 verified header within buffer   */
      FLACHeaderMarker *best_header; /**< highest scoring header within buffer  */
      int nb_headers_found;          /**< number of headers found in the last
                                          flac_parse() call                     */
      int nb_headers_buffered;       /**< number of headers that are buffered   */
      int best_header_valid;         /**< flag set when the parser returns junk;
                                          if set return best_header next time   */
      FifoBuffer fifo_buf;           /**< buffer to store all data until headers
                                          can be verified                       */
      int end_padded;                /**< specifies if fifo_buf's end is padded */
      uint8_t *wrap_buf;             /**< general fifo read buffer when wrapped */
      int wrap_buf_allocated_size;   /**< actual allocated size of the buffer   */
      FLACFrameInfo last_fi;         /**< last decoded frame header info        */
      int last_fi_valid;             /**< set if last_fi is valid               */
  } FLACParseContext;
  
  static int frame_header_is_valid(AVCodecContext *avctx, const uint8_t *buf,
                                   FLACFrameInfo *fi)
  {
      GetBitContext gb;
      uint8_t subframe_type;
  
      // header plus one byte from first subframe
      init_get_bits(&gb, buf, MAX_FRAME_VERIFY_SIZE * 8);
      if (ff_flac_decode_frame_header(avctx, &gb, fi, 127)) {
          return 0;
      }
      // subframe zero bit
      if (get_bits1(&gb) != 0) {
          return 0;
      }
      // subframe type
      // 000000 : SUBFRAME_CONSTANT
      // 000001 : SUBFRAME_VERBATIM
      // 00001x : reserved
      // 0001xx : reserved
      // 001xxx : if(xxx <= 4) SUBFRAME_FIXED, xxx=order ; else reserved
      // 01xxxx : reserved
      // 1xxxxx : SUBFRAME_LPC, xxxxx=order-1
      subframe_type = get_bits(&gb, 6);
      if (!(subframe_type == 0 ||
            subframe_type == 1 ||
            ((subframe_type >= 8) && (subframe_type <= 12)) ||
            (subframe_type >= 32))) {
          return 0;
      }
  
      return 1;
  }
  
  static size_t flac_fifo_size(const FifoBuffer *f)
  {
      if (f->wptr <= f->rptr && !f->empty)
          return (f->wptr - f->buffer) + (f->end - f->rptr);
      return f->wptr - f->rptr;
  }
  
  static size_t flac_fifo_space(const FifoBuffer *f)
  {
      return f->end - f->buffer - flac_fifo_size(f);
  }
  
  /**
   * Non-destructive fast fifo pointer fetching
   * Returns a pointer from the specified offset.
   * If possible the pointer points within the fifo buffer.
   * Otherwise (if it would cause a wrap around,) a pointer to a user-specified
   * buffer is used.
   * The pointer can be NULL.  In any case it will be reallocated to hold the size.
   * If the returned pointer will be used after subsequent calls to flac_fifo_read_wrap
   * then the subsequent calls should pass in a different wrap_buf so as to not
   * overwrite the contents of the previous wrap_buf.
   * This function is based on av_fifo_generic_read, which is why there is a comment
   * about a memory barrier for SMP.
   */
  static uint8_t *flac_fifo_read_wrap(FLACParseContext *fpc, int offset, int len,
                                      uint8_t **wrap_buf, int *allocated_size)
  {
      FifoBuffer   *f   = &fpc->fifo_buf;
      uint8_t *start    = f->rptr + offset;
      uint8_t *tmp_buf;
  
      if (start >= f->end)
          start -= f->end - f->buffer;
      if (f->end - start >= len)
          return start;
  
      tmp_buf = av_fast_realloc(*wrap_buf, allocated_size, len);
  
      if (!tmp_buf) {
          av_log(fpc->avctx, AV_LOG_ERROR,
                 "couldn't reallocate wrap buffer of size %d", len);
          return NULL;
      }
      *wrap_buf = tmp_buf;
      do {
          int seg_len = FFMIN(f->end - start, len);
          memcpy(tmp_buf, start, seg_len);
          tmp_buf = (uint8_t*)tmp_buf + seg_len;
  // memory barrier needed for SMP here in theory
  
          start += seg_len - (f->end - f->buffer);
          len -= seg_len;
      } while (len > 0);
  
      return *wrap_buf;
  }
  
  /**
   * Return a pointer in the fifo buffer where the offset starts at until
   * the wrap point or end of request.
   * len will contain the valid length of the returned buffer.
   * A second call to flac_fifo_read (with new offset and len) should be called
   * to get the post-wrap buf if the returned len is less than the requested.
   **/
  static uint8_t *flac_fifo_read(FifoBuffer *f, int offset, int *len)
  {
      uint8_t *start    = f->rptr + offset;
  
      if (start >= f->end)
          start -= f->end - f->buffer;
      *len = FFMIN(*len, f->end - start);
      return start;
  }
  
  static int flac_fifo_grow(FifoBuffer *f, size_t inc)
  {
      size_t size_old = f->end - f->buffer;
      size_t offset_r = f->rptr - f->buffer;
      size_t offset_w = f->wptr - f->buffer;
      size_t size_new;
  
      uint8_t *tmp;
  
      if (size_old > SIZE_MAX - inc)
          return AVERROR(EINVAL);
      size_new = size_old + inc;
  
      tmp = av_realloc(f->buffer, size_new);
      if (!tmp)
          return AVERROR(ENOMEM);
  
      // move the data from the beginning of the ring buffer
      // to the newly allocated space
      if (offset_w <= offset_r && !f->empty) {
          const size_t copy = FFMIN(inc, offset_w);
          memcpy(tmp + size_old, tmp, copy);
          if (copy < offset_w) {
              memmove(tmp, tmp + copy, offset_w - copy);
              offset_w -= copy;
          } else
              offset_w = size_old + copy;
      }
  
      f->buffer = tmp;
      f->end    = f->buffer + size_new;
      f->rptr   = f->buffer + offset_r;
      f->wptr   = f->buffer + offset_w;
  
      return 0;
  }
  
  static int flac_fifo_write(FifoBuffer *f, const uint8_t *src, size_t size)
  {
      uint8_t *wptr;
  
      if (flac_fifo_space(f) < size) {
          int ret = flac_fifo_grow(f, FFMAX(flac_fifo_size(f), size));
          if (ret < 0)
              return ret;
      }
  
      if (size)
          f->empty = 0;
  
      wptr = f->wptr;
      do {
          size_t len = FFMIN(f->end - wptr, size);
          memcpy(wptr, src, len);
          src  += len;
          wptr += len;
          if (wptr >= f->end)
              wptr = f->buffer;
          size    -= len;
      } while (size > 0);
  
      f->wptr = wptr;
  
      return 0;
  }
  
  static void flac_fifo_drain(FifoBuffer *f, size_t size)
  {
      size_t size_cur = flac_fifo_size(f);
  
      av_assert0(size_cur >= size);
      if (size_cur == size)
          f->empty = 1;
  
      f->rptr += size;
      if (f->rptr >= f->end)
          f->rptr -= f->end - f->buffer;
  }
  
  static int flac_fifo_alloc(FifoBuffer *f, size_t size)
  {
      memset(f, 0, sizeof(*f));
  
      f->buffer = av_realloc(NULL, size);
      if (!f->buffer)
          return AVERROR(ENOMEM);
  
      f->wptr = f->buffer;
      f->rptr = f->buffer;
      f->end  = f->buffer + size;
  
      f->empty = 1;
  
      return 0;
  }
  
  static void flac_fifo_free(FifoBuffer *f)
  {
      av_freep(&f->buffer);
      memset(f, 0, sizeof(*f));
  }
  
  static int find_headers_search_validate(FLACParseContext *fpc, int offset)
  {
      FLACFrameInfo fi;
      uint8_t *header_buf;
      int size = 0;
      header_buf = flac_fifo_read_wrap(fpc, offset,
                                       MAX_FRAME_VERIFY_SIZE + AV_INPUT_BUFFER_PADDING_SIZE,
                                       &fpc->wrap_buf,
                                       &fpc->wrap_buf_allocated_size);
      if (frame_header_is_valid(fpc->avctx, header_buf, &fi)) {
          FLACHeaderMarker **end_handle = &fpc->headers;
          int i;
  
          size = 0;
          while (*end_handle) {
              end_handle = &(*end_handle)->next;
              size++;
          }
  
          *end_handle = av_mallocz(sizeof(**end_handle));
          if (!*end_handle) {
              av_log(fpc->avctx, AV_LOG_ERROR,
                     "couldn't allocate FLACHeaderMarker\n");
              return AVERROR(ENOMEM);
          }
          (*end_handle)->fi     = fi;
          (*end_handle)->offset = offset;
  
          for (i = 0; i < FLAC_MAX_SEQUENTIAL_HEADERS; i++)
              (*end_handle)->link_penalty[i] = FLAC_HEADER_NOT_PENALIZED_YET;
  
          fpc->nb_headers_found++;
          size++;
      }
      return size;
  }
  
  static int find_headers_search(FLACParseContext *fpc, uint8_t *buf,
                                 int buf_size, int search_start)
  {
      int size = 0, mod_offset = (buf_size - 1) % 4, i, j;
      uint32_t x;
  
      for (i = 0; i < mod_offset; i++) {
          if ((AV_RB16(buf + i) & 0xFFFE) == 0xFFF8) {
              int ret = find_headers_search_validate(fpc, search_start + i);
              size = FFMAX(size, ret);
          }
      }
  
      for (; i < buf_size - 1; i += 4) {
          x = AV_RN32(buf + i);
          if (((x & ~(x + 0x01010101)) & 0x80808080)) {
              for (j = 0; j < 4; j++) {
                  if ((AV_RB16(buf + i + j) & 0xFFFE) == 0xFFF8) {
                      int ret = find_headers_search_validate(fpc, search_start + i + j);
                      size = FFMAX(size, ret);
                  }
              }
          }
      }
      return size;
  }
  
  static int find_new_headers(FLACParseContext *fpc, int search_start)
  {
      FLACHeaderMarker *end;
      int search_end, size = 0, read_len, temp;
      uint8_t *buf;
      fpc->nb_headers_found = 0;
  
      /* Search for a new header of at most 16 bytes. */
      search_end = flac_fifo_size(&fpc->fifo_buf) - (MAX_FRAME_HEADER_SIZE - 1);
      read_len   = search_end - search_start + 1;
      buf        = flac_fifo_read(&fpc->fifo_buf, search_start, &read_len);
      size       = find_headers_search(fpc, buf, read_len, search_start);
      search_start += read_len - 1;
  
      /* If fifo end was hit do the wrap around. */
      if (search_start != search_end) {
          uint8_t wrap[2];
  
          wrap[0]  = buf[read_len - 1];
          /* search_start + 1 is the post-wrap offset in the fifo. */
          read_len = search_end - (search_start + 1) + 1;
  
          buf      = flac_fifo_read(&fpc->fifo_buf, search_start + 1, &read_len);
          wrap[1]  = buf[0];
  
          if ((AV_RB16(wrap) & 0xFFFE) == 0xFFF8) {
              temp = find_headers_search_validate(fpc, search_start);
              size = FFMAX(size, temp);
          }
          search_start++;
  
          /* Continue to do the last half of the wrap. */
          temp     = find_headers_search(fpc, buf, read_len, search_start);
          size     = FFMAX(size, temp);
          search_start += read_len - 1;
      }
  
      /* Return the size even if no new headers were found. */
      if (!size && fpc->headers)
          for (end = fpc->headers; end; end = end->next)
              size++;
      return size;
  }
  
  static int check_header_fi_mismatch(FLACParseContext  *fpc,
                                      FLACFrameInfo     *header_fi,
                                      FLACFrameInfo     *child_fi,
                                      int                log_level_offset)
  {
      int deduction = 0;
      if (child_fi->samplerate != header_fi->samplerate) {
          deduction += FLAC_HEADER_CHANGED_PENALTY;
          av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
                 "sample rate change detected in adjacent frames\n");
      }
      if (child_fi->bps != header_fi->bps) {
          deduction += FLAC_HEADER_CHANGED_PENALTY;
          av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
                 "bits per sample change detected in adjacent frames\n");
      }
      if (child_fi->is_var_size != header_fi->is_var_size) {
          /* Changing blocking strategy not allowed per the spec */
          deduction += FLAC_HEADER_BASE_SCORE;
          av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
                 "blocking strategy change detected in adjacent frames\n");
      }
      if (child_fi->channels != header_fi->channels) {
          deduction += FLAC_HEADER_CHANGED_PENALTY;
          av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
                 "number of channels change detected in adjacent frames\n");
      }
      return deduction;
  }
  
  static int check_header_mismatch(FLACParseContext  *fpc,
                                   FLACHeaderMarker  *header,
                                   FLACHeaderMarker  *child,
                                   int                log_level_offset)
  {
      FLACFrameInfo  *header_fi = &header->fi, *child_fi = &child->fi;
      int deduction, deduction_expected = 0, i;
      deduction = check_header_fi_mismatch(fpc, header_fi, child_fi,
                                           log_level_offset);
      /* Check sample and frame numbers. */
      if ((child_fi->frame_or_sample_num - header_fi->frame_or_sample_num
           != header_fi->blocksize) &&
          (child_fi->frame_or_sample_num
           != header_fi->frame_or_sample_num + 1)) {
          FLACHeaderMarker *curr;
          int64_t expected_frame_num, expected_sample_num;
          /* If there are frames in the middle we expect this deduction,
             as they are probably valid and this one follows it */
  
          expected_frame_num = expected_sample_num = header_fi->frame_or_sample_num;
          curr = header;
          while (curr != child) {
              /* Ignore frames that failed all crc checks */
              for (i = 0; i < FLAC_MAX_SEQUENTIAL_HEADERS; i++) {
                  if (curr->link_penalty[i] < FLAC_HEADER_CRC_FAIL_PENALTY) {
                      expected_frame_num++;
                      expected_sample_num += curr->fi.blocksize;
                      break;
                  }
              }
              curr = curr->next;
          }
  
          if (expected_frame_num  == child_fi->frame_or_sample_num ||
              expected_sample_num == child_fi->frame_or_sample_num)
              deduction_expected = deduction ? 0 : 1;
  
          deduction += FLAC_HEADER_CHANGED_PENALTY;
          av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
                     "sample/frame number mismatch in adjacent frames\n");
      }
  
      /* If we have suspicious headers, check the CRC between them */
      if (deduction && !deduction_expected) {
          FLACHeaderMarker *curr;
          int read_len;
          uint8_t *buf;
          uint32_t crc = 1;
          int inverted_test = 0;
  
          /* Since CRC is expensive only do it if we haven't yet.
             This assumes a CRC penalty is greater than all other check penalties */
          curr = header->next;
          for (i = 0; i < FLAC_MAX_SEQUENTIAL_HEADERS && curr != child; i++)
              curr = curr->next;
  
          if (header->link_penalty[i] < FLAC_HEADER_CRC_FAIL_PENALTY ||
              header->link_penalty[i] == FLAC_HEADER_NOT_PENALIZED_YET) {
              FLACHeaderMarker *start, *end;
  
              /* Although overlapping chains are scored, the crc should never
                 have to be computed twice for a single byte. */
              start = header;
              end   = child;
              if (i > 0 &&
                  header->link_penalty[i - 1] >= FLAC_HEADER_CRC_FAIL_PENALTY) {
                  while (start->next != child)
                      start = start->next;
                  inverted_test = 1;
              } else if (i > 0 &&
                         header->next->link_penalty[i-1] >=
                         FLAC_HEADER_CRC_FAIL_PENALTY ) {
                  end = header->next;
                  inverted_test = 1;
              }
  
              read_len = end->offset - start->offset;
              buf      = flac_fifo_read(&fpc->fifo_buf, start->offset, &read_len);
              crc      = av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0, buf, read_len);
              read_len = (end->offset - start->offset) - read_len;
  
              if (read_len) {
                  buf = flac_fifo_read(&fpc->fifo_buf, end->offset - read_len, &read_len);
                  crc = av_crc(av_crc_get_table(AV_CRC_16_ANSI), crc, buf, read_len);
              }
          }
  
          if (!crc ^ !inverted_test) {
              deduction += FLAC_HEADER_CRC_FAIL_PENALTY;
              av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
                     "crc check failed from offset %i (frame %"PRId64") to %i (frame %"PRId64")\n",
                     header->offset, header_fi->frame_or_sample_num,
                     child->offset, child_fi->frame_or_sample_num);
          }
      }
      return deduction;
  }
  
  /**
   * Score a header.
   *
   * Give FLAC_HEADER_BASE_SCORE points to a frame for existing.
   * If it has children, (subsequent frames of which the preceding CRC footer
   * validates against this one,) then take the maximum score of the children,
   * with a penalty of FLAC_HEADER_CHANGED_PENALTY applied for each change to
   * bps, sample rate, channels, but not decorrelation mode, or blocksize,
   * because it can change often.
   **/
  static int score_header(FLACParseContext *fpc, FLACHeaderMarker *header)
  {
      FLACHeaderMarker *child;
      int dist = 0;
      int child_score;
      int base_score = FLAC_HEADER_BASE_SCORE;
      if (header->max_score != FLAC_HEADER_NOT_SCORED_YET)
          return header->max_score;
  
      /* Modify the base score with changes from the last output header */
      if (fpc->last_fi_valid) {
          /* Silence the log since this will be repeated if selected */
          base_score -= check_header_fi_mismatch(fpc, &fpc->last_fi, &header->fi,
                                                 AV_LOG_DEBUG);
      }
  
      header->max_score = base_score;
  
      /* Check and compute the children's scores. */
      child = header->next;
      for (dist = 0; dist < FLAC_MAX_SEQUENTIAL_HEADERS && child; dist++) {
          /* Look at the child's frame header info and penalize suspicious
             changes between the headers. */
          if (header->link_penalty[dist] == FLAC_HEADER_NOT_PENALIZED_YET) {
              header->link_penalty[dist] = check_header_mismatch(fpc, header,
                                                                 child, AV_LOG_DEBUG);
          }
          child_score = score_header(fpc, child) - header->link_penalty[dist];
  
          if (FLAC_HEADER_BASE_SCORE + child_score > header->max_score) {
              /* Keep the child because the frame scoring is dynamic. */
              header->best_child = child;
              header->max_score  = base_score + child_score;
          }
          child = child->next;
      }
  
      return header->max_score;
  }
  
  static void score_sequences(FLACParseContext *fpc)
  {
      FLACHeaderMarker *curr;
      int best_score = 0;//FLAC_HEADER_NOT_SCORED_YET;
      /* First pass to clear all old scores. */
      for (curr = fpc->headers; curr; curr = curr->next)
          curr->max_score = FLAC_HEADER_NOT_SCORED_YET;
  
      /* Do a second pass to score them all. */
      for (curr = fpc->headers; curr; curr = curr->next) {
          if (score_header(fpc, curr) > best_score) {
              fpc->best_header = curr;
              best_score       = curr->max_score;
          }
      }
  }
  
  static int get_best_header(FLACParseContext *fpc, const uint8_t **poutbuf,
                             int *poutbuf_size)
  {
      FLACHeaderMarker *header = fpc->best_header;
      FLACHeaderMarker *child  = header->best_child;
      if (!child) {
          *poutbuf_size = flac_fifo_size(&fpc->fifo_buf) - header->offset;
      } else {
          *poutbuf_size = child->offset - header->offset;
  
          /* If the child has suspicious changes, log them */
          check_header_mismatch(fpc, header, child, 0);
      }
  
      if (header->fi.channels != fpc->avctx->channels ||
          !fpc->avctx->channel_layout) {
          fpc->avctx->channels = header->fi.channels;
          ff_flac_set_channel_layout(fpc->avctx);
      }
      fpc->avctx->sample_rate = header->fi.samplerate;
      fpc->pc->duration       = header->fi.blocksize;
      *poutbuf = flac_fifo_read_wrap(fpc, header->offset, *poutbuf_size,
                                          &fpc->wrap_buf,
                                          &fpc->wrap_buf_allocated_size);
  
      if (fpc->pc->flags & PARSER_FLAG_USE_CODEC_TS) {
          if (header->fi.is_var_size)
            fpc->pc->pts = header->fi.frame_or_sample_num;
          else if (header->best_child)
            fpc->pc->pts = header->fi.frame_or_sample_num * header->fi.blocksize;
      }
  
      fpc->best_header_valid = 0;
      fpc->last_fi_valid = 1;
      fpc->last_fi = header->fi;
  
      /* Return the negative overread index so the client can compute pos.
         This should be the amount overread to the beginning of the child */
      if (child)
          return child->offset - flac_fifo_size(&fpc->fifo_buf);
      return 0;
  }
  
  static int flac_parse(AVCodecParserContext *s, AVCodecContext *avctx,
                        const uint8_t **poutbuf, int *poutbuf_size,
                        const uint8_t *buf, int buf_size)
  {
      FLACParseContext *fpc = s->priv_data;
      FLACHeaderMarker *curr;
      int nb_headers;
      const uint8_t *read_end   = buf;
      const uint8_t *read_start = buf;
  
      if (s->flags & PARSER_FLAG_COMPLETE_FRAMES) {
          FLACFrameInfo fi;
          if (frame_header_is_valid(avctx, buf, &fi)) {
              s->duration = fi.blocksize;
              if (!avctx->sample_rate)
                  avctx->sample_rate = fi.samplerate;
              if (fpc->pc->flags & PARSER_FLAG_USE_CODEC_TS) {
                  fpc->pc->pts = fi.frame_or_sample_num;
                  if (!fi.is_var_size)
                    fpc->pc->pts *= fi.blocksize;
              }
          }
          *poutbuf      = buf;
          *poutbuf_size = buf_size;
          return buf_size;
      }
  
      fpc->avctx = avctx;
      if (fpc->best_header_valid)
          return get_best_header(fpc, poutbuf, poutbuf_size);
  
      /* If a best_header was found last call remove it with the buffer data. */
      if (fpc->best_header && fpc->best_header->best_child) {
          FLACHeaderMarker *temp;
          FLACHeaderMarker *best_child = fpc->best_header->best_child;
  
          /* Remove headers in list until the end of the best_header. */
          for (curr = fpc->headers; curr != best_child; curr = temp) {
              if (curr != fpc->best_header) {
                  av_log(avctx, AV_LOG_DEBUG,
                         "dropping low score %i frame header from offset %i to %i\n",
                         curr->max_score, curr->offset, curr->next->offset);
              }
              temp = curr->next;
              av_free(curr);
              fpc->nb_headers_buffered--;
          }
          /* Release returned data from ring buffer. */
          flac_fifo_drain(&fpc->fifo_buf, best_child->offset);
  
          /* Fix the offset for the headers remaining to match the new buffer. */
          for (curr = best_child->next; curr; curr = curr->next)
              curr->offset -= best_child->offset;
  
          best_child->offset = 0;
          fpc->headers       = best_child;
          if (fpc->nb_headers_buffered >= FLAC_MIN_HEADERS) {
              fpc->best_header = best_child;
              return get_best_header(fpc, poutbuf, poutbuf_size);
          }
          fpc->best_header   = NULL;
      } else if (fpc->best_header) {
          /* No end frame no need to delete the buffer; probably eof */
          FLACHeaderMarker *temp;
  
          for (curr = fpc->headers; curr != fpc->best_header; curr = temp) {
              temp = curr->next;
              av_free(curr);
              fpc->nb_headers_buffered--;
          }
          fpc->headers = fpc->best_header->next;
          av_freep(&fpc->best_header);
          fpc->nb_headers_buffered--;
      }
  
      /* Find and score new headers.                                     */
      /* buf_size is zero when flushing, so check for this since we do   */
      /* not want to try to read more input once we have found the end.  */
      /* Also note that buf can't be NULL.                               */
      while ((buf_size && read_end < buf + buf_size &&
              fpc->nb_headers_buffered < FLAC_MIN_HEADERS)
             || (!buf_size && !fpc->end_padded)) {
          int start_offset, ret;
  
          /* Pad the end once if EOF, to check the final region for headers. */
          if (!buf_size) {
              fpc->end_padded = 1;
              read_end = read_start + MAX_FRAME_HEADER_SIZE;
          } else {
              /* The maximum read size is the upper-bound of what the parser
                 needs to have the required number of frames buffered */
              int nb_desired = FLAC_MIN_HEADERS - fpc->nb_headers_buffered + 1;
              read_end       = read_end + FFMIN(buf + buf_size - read_end,
                                                nb_desired * FLAC_AVG_FRAME_SIZE);
          }
  
          if (!flac_fifo_space(&fpc->fifo_buf) &&
              flac_fifo_size(&fpc->fifo_buf) / FLAC_AVG_FRAME_SIZE >
              fpc->nb_headers_buffered * 20) {
              /* There is less than one valid flac header buffered for 20 headers
               * buffered. Therefore the fifo is most likely filled with invalid
               * data and the input is not a flac file. */
              goto handle_error;
          }
  
          /* Fill the buffer. */
          if (buf_size) {
              ret = flac_fifo_write(&fpc->fifo_buf, read_start,
                                    read_end - read_start);
          } else {
              int8_t pad[MAX_FRAME_HEADER_SIZE] = { 0 };
              ret = flac_fifo_write(&fpc->fifo_buf, pad, sizeof(pad));
          }
          if (ret < 0) {
              av_log(avctx, AV_LOG_ERROR, "Error buffering data\n");
              goto handle_error;
          }
  
          /* Tag headers and update sequences. */
          start_offset = flac_fifo_size(&fpc->fifo_buf) -
                         ((read_end - read_start) + (MAX_FRAME_HEADER_SIZE - 1));
          start_offset = FFMAX(0, start_offset);
          nb_headers   = find_new_headers(fpc, start_offset);
  
          if (nb_headers < 0) {
              av_log(avctx, AV_LOG_ERROR,
                     "find_new_headers couldn't allocate FLAC header\n");
              goto handle_error;
          }
  
          fpc->nb_headers_buffered = nb_headers;
          /* Wait till FLAC_MIN_HEADERS to output a valid frame. */
          if (!fpc->end_padded && fpc->nb_headers_buffered < FLAC_MIN_HEADERS) {
              if (read_end < buf + buf_size) {
                  read_start = read_end;
                  continue;
              } else {
                  goto handle_error;
              }
          }
  
          /* If headers found, update the scores since we have longer chains. */
          if (fpc->end_padded || fpc->nb_headers_found)
              score_sequences(fpc);
  
          /* restore the state pre-padding */
          if (fpc->end_padded) {
              int empty = flac_fifo_size(&fpc->fifo_buf) == MAX_FRAME_HEADER_SIZE;
              int warp = fpc->fifo_buf.wptr - fpc->fifo_buf.buffer < MAX_FRAME_HEADER_SIZE;
              /* HACK: drain the tail of the fifo */
              fpc->fifo_buf.wptr -= MAX_FRAME_HEADER_SIZE;
              if (warp) {
                  fpc->fifo_buf.wptr += fpc->fifo_buf.end -
                      fpc->fifo_buf.buffer;
              }
              fpc->fifo_buf.empty = empty;
              read_start = read_end = NULL;
          }
      }
  
      for (curr = fpc->headers; curr; curr = curr->next) {
          if (!fpc->best_header || curr->max_score > fpc->best_header->max_score) {
              fpc->best_header = curr;
          }
      }
  
      if (fpc->best_header && fpc->best_header->max_score <= 0) {
          // Only accept a bad header if there is no other option to continue
          if (!buf_size || read_end != buf || fpc->nb_headers_buffered < FLAC_MIN_HEADERS)
              fpc->best_header = NULL;
      }
  
      if (fpc->best_header) {
          fpc->best_header_valid = 1;
          if (fpc->best_header->offset > 0) {
              /* Output a junk frame. */
              av_log(avctx, AV_LOG_DEBUG, "Junk frame till offset %i\n",
                     fpc->best_header->offset);
  
              /* Set duration to 0. It is unknown or invalid in a junk frame. */
              s->duration   = 0;
              *poutbuf_size = fpc->best_header->offset;
              *poutbuf      = flac_fifo_read_wrap(fpc, 0, *poutbuf_size,
                                                  &fpc->wrap_buf,
                                                  &fpc->wrap_buf_allocated_size);
              return buf_size ? (read_end - buf) : (fpc->best_header->offset -
                                                    flac_fifo_size(&fpc->fifo_buf));
          }
          if (!buf_size)
              return get_best_header(fpc, poutbuf, poutbuf_size);
      }
  
  handle_error:
      *poutbuf      = NULL;
      *poutbuf_size = 0;
      return buf_size ? read_end - buf : 0;
  }
  
  static av_cold int flac_parse_init(AVCodecParserContext *c)
  {
      FLACParseContext *fpc = c->priv_data;
      int ret;
  
      fpc->pc = c;
      /* There will generally be FLAC_MIN_HEADERS buffered in the fifo before
         it drains.  This is allocated early to avoid slow reallocation. */
      ret = flac_fifo_alloc(&fpc->fifo_buf, (FLAC_MIN_HEADERS + 3) * FLAC_AVG_FRAME_SIZE);
      if (ret < 0) {
          av_log(fpc->avctx, AV_LOG_ERROR,
                  "couldn't allocate fifo_buf\n");
          return AVERROR(ENOMEM);
      }
      return 0;
  }
  
  static void flac_parse_close(AVCodecParserContext *c)
  {
      FLACParseContext *fpc = c->priv_data;
      FLACHeaderMarker *curr = fpc->headers, *temp;
  
      while (curr) {
          temp = curr->next;
          av_free(curr);
          curr = temp;
      }
      fpc->headers = NULL;
      flac_fifo_free(&fpc->fifo_buf);
      av_freep(&fpc->wrap_buf);
  }
  
  const AVCodecParser ff_flac_parser = {
      .codec_ids      = { AV_CODEC_ID_FLAC },
      .priv_data_size = sizeof(FLACParseContext),
      .parser_init    = flac_parse_init,
      .parser_parse   = flac_parse,
      .parser_close   = flac_parse_close,
  };
  