Function free_bitrate

modules/data/mp3/libmad/frame.c:234–290

* NAME: free_bitrate() * DESCRIPTION: attempt to discover the bitstream's free bitrate */

 * DESCRIPTION:	attempt to discover the bitstream's free bitrate
 */
static
int free_bitrate(struct mad_stream *stream, struct mad_header const *header)
{
  struct mad_bitptr keep_ptr;
  unsigned long rate = 0;
  unsigned int pad_slot, slots_per_frame;
  unsigned char const *ptr = 0;

  keep_ptr = stream->ptr;

  pad_slot = (header->flags & MAD_FLAG_PADDING) ? 1 : 0;
  slots_per_frame = (header->layer == MAD_LAYER_III &&
		     (header->flags & MAD_FLAG_LSF_EXT)) ? 72 : 144;

  while (mad_stream_sync(stream) == 0) {
    struct mad_stream peek_stream;
    struct mad_header peek_header;

    peek_stream = *stream;
    peek_header = *header;

    if (decode_header(&peek_header, &peek_stream) == 0 &&
	peek_header.layer == header->layer &&
	peek_header.samplerate == header->samplerate) {
      unsigned int N;

      ptr = mad_bit_nextbyte(&stream->ptr);

      N = ptr - stream->this_frame;

      if (header->layer == MAD_LAYER_I) {
	rate = (unsigned long) header->samplerate *
	  (N - 4 * pad_slot + 4) / 48 / 1000;
      }
      else {
	rate = (unsigned long) header->samplerate *
	  (N - pad_slot + 1) / slots_per_frame / 1000;
      }

      if (rate >= 8)
	break;
    }

    mad_bit_skip(&stream->ptr, 8);
  }

  stream->ptr = keep_ptr;

  if (rate < 8 || (header->layer == MAD_LAYER_III && rate > 640)) {
    stream->error = MAD_ERROR_LOSTSYNC;
    return -1;
  }

  stream->freerate = rate * 1000;

  return 0;
}