ffmpeg ts 封装 aac 中推断出的两个结论

6290阅读　0评论2012-03-09　zylthinking
分类：LINUX


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  1. static struct muxer* init_muxer(enum CodecID id, const char* name, const char* ext, struct audio_param* in){
  2. int bufid = buf_length_register(1024);
  3. if(bufid == -1){
  4. return NULL;
  5. }
  7. struct muxer* muxerp = (struct muxer *) malloc(sizeof(struct muxer));
  8. if(muxerp == NULL){
  9. return NULL;
  10. }
  12. INIT_LIST_HEAD(&muxerp->head);
  13. memset(muxerp->line, 0, sizeof(muxerp->line));
  14. muxerp->cur_buf = NULL;
  15. muxerp->bufid = bufid;
  16. muxerp->avctx = NULL;
  18. AVIOContext* ioctx = NULL;
  19. AVStream *st = NULL;
  20. AVFormatContext* fmtctx = NULL;
  22. avformat_alloc_output_context2(&fmtctx, NULL, name, ext);
  23. if(fmtctx == NULL){
  24. goto LABEL;
  25. }
  27. st = av_new_stream(fmtctx, 0);
  28. if(st == NULL){
  29. goto LABEL;
  30. }
  31. st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
  32. st->codec->codec_id = id;
  33. st->codec->frame_size = in->spf; // this should be the pcm frame size
  34. st->codec->sample_rate = in->rate; // this should be the pcm sample rate
  35. st->codec->bit_rate = in->bps; // this should be output stream's bitrate
  36. st->codec->channels = in->chans;
  38. ioctx = avio_alloc_context(&muxerp->line[0], sizeof(muxerp->line), 0,
  39. (void *) muxerp, NULL, write_packet, NULL);
  40. if(ioctx == NULL){
  41. goto LABEL;
  42. }
  43. fmtctx->pb = ioctx;
  45. if(0 != avformat_write_header(fmtctx, NULL)){
  46. goto LABEL;
  47. }
  49. muxerp->avctx = fmtctx;
  50. return muxerp;
  51. LABEL:
  52. if(fmtctx){
  53. avformat_free_context(fmtctx);
  54. if(ioctx){
  55. av_free(ioctx);
  56. }
  57. }
  58. free(muxerp);
  59. return NULL;
  60. }
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  1. st->codec->frame_size = in->spf; // this should be the pcm frame size
  2. st->codec->sample_rate = in->rate; // this should be the pcm sample rate
由以下代码推导出来：
  1. if (pcr_st->codec->codec_type == AVMEDIA_TYPE_AUDIO) {
  2. if (!pcr_st->codec->frame_size) {
  3. av_log(s, AV_LOG_WARNING, "frame size not set\n");
  4. service->pcr_packet_period =
  5. pcr_st->codec->sample_rate/(10*512);
  6. } else {
  7. service->pcr_packet_period =
  8. pcr_st->codec->sample_rate/(10*pcr_st->codec->frame_size);
  9. }

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  1. st->codec->bit_rate = in->bps; // this should be output stream's bitrate
  2. 由以下代码推导出来：

  4. static int get_audio_frame_size(AVCodecContext *enc, int size)
  5. {
  6. int frame_size;
  8. if(enc->codec_id == CODEC_ID_VORBIS)
  9. return -1;
  11. if (enc->frame_size <= 1) {
  12. int bits_per_sample = av_get_bits_per_sample(enc->codec_id);
  14. if (bits_per_sample) {
  15. if (enc->channels == 0)
  16. return -1;
  17. frame_size = (size << 3) / (bits_per_sample * enc->channels);
  18. } else {
  19. /* used for example by ADPCM codecs */
  20. if (enc->bit_rate == 0)
  21. return -1;
  22. frame_size = ((int64_t)size * 8 * enc->sample_rate) / enc->bit_rate;
  23. }
  24. } else {
  25. frame_size = enc->frame_size;
  26. }
  27. return frame_size;

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