1. FFmpeg
2012-04-01 Eric

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.