![structure
AVFormatContext
Stream[n] AVStream
AVCodecContext
Codec
Codec
Bitrate
FPS
……….
Sample_rate
…..](https://image.slidesharecdn.com/ffmpeg-120807194432-phpapp02/85/FFmpeg-5-320.jpg)
FFmpeg
- 2. outline work flow process structure my SOP
- 3. work flow process Input Video Data File Demuxer stream Decoder Audio Data Subtitle Data
- 4. work flow process Output Video Data File Muxer stream Encoder Audio Data Subtitle Data
- 5. structure AVFormatContext Stream[n] AVStream AVCodecContext Codec Codec Bitrate FPS ………. Sample_rate …..
- 6. my SOP
- 7. step 1 include headers extern "C" { #include "libavformat/avformat.h" #include "libavutil/base64.h" } initial ffmpeg av_register_all()
- 8. step 2 link library FFMPEGLIBS = -lavcodec -lavformat -lavutil
- 9. step 3 set up out format AVFormatContext avformat_alloc_context AVOutputFormat av_guess_format if format did not support, please set up configure file.
- 10. step 4 we need to prepare some codec structures. AVFormatContext av_new_stream(c, channel) video audio AVStream AVStream video audio stream->codec AVCodecContext AVCodecContext
- 11. step 5 set up video codec msrAVCodecContextVideo->codec_id = CODEC_ID_MPEG4; msrAVCodecContextVideo->codec_type = CODEC_TYPE_VIDEO; msrAVCodecContextVideo->bit_rate= iBitrate; msrAVCodecContextVideo->width= iWidth; msrAVCodecContextVideo->height= iHeight; msrAVCodecContextVideo->time_base.den = iFps; msrAVCodecContextVideo->time_base.num = 1; msrAVCodecContextVideo->gop_size= iFps; msrAVCodecContextVideo->pix_fmt= PIX_FMT_YUV420P; msrAVCodecContextVideo->max_b_frames=0;
- 12. step 6 set up audio codec msrAVCodecContextAudio = msrAVStreamAudio->codec; msrAVCodecContextAudio->codec_id = CODEC_ID_PCM_S16LE; msrAVCodecContextAudio->codec_type = CODEC_TYPE_AUDIO; msrAVCodecContextAudio->bit_rate = 128000 ; msrAVCodecContextAudio->sample_rate = 8000; msrAVCodecContextAudio->channels = 1;
- 13. step 7 open file descriptor and write header if(url_fopen(&sAVFormatContext->pb, pathName, URL_WRONLY) < 0) { //error handle } av_write_header(sAVFormatContext); the pathName can be following file://tmp/aaaa tcp://x99 udp://x88
- 14. step 8 try to write some data AVPacket sePacket; av_init_packet(&sePacket); sePacket.flags |= PKT_FLAG_KEY; sePacket.stream_index = channel; //which channel sePacket.data = data; sePacket.size = len; //sePacket.pts = ???; //explain later av_write_frame(sAVFormatContext, &sePacket); printf(“pts: %dn”, sePacket.pts); av_free_packet(&sePacket); if(sAVFormatContext->pb->error < 0) { //error handle }
- 15. step 9 close file descriptor if(sAVFormatContext->pb != NULL){ av_write_trailer(sAVFormatContext); if(url_fclose(sAVFormatContext->pb) < 0) { perror("Close file failed."); } sAVFormatContext->pb = NULL; }
- 16. step 10 get pts against different codec 1. let ffmpeg print and simulate it. 2. see RFC. 3. find pts calculate from ffmpeg source code.
- 17. Thanks a lot.