本文记录一个基于FFmpeg的视音频分离器（Simplest FFmpeg demuxer）。视音频分离器（Demuxer）即是将封装格式数据（例如MKV）中的视频压缩数据（例如H.264）和音频压缩数据（例如AAC）分离开。如图所示。在这个过程中并不涉及到编码和解码。
/**
* 最简单的基于FFmpeg的视音频分离器
* Simplest FFmpeg Demuxer
*
* 雷霄骅 Lei Xiaohua
* leixiaohua1020@126.com
* 中国传媒大学/数字电视技术
* Communication University of China / Digital TV Technology
* http://blog.csdn.net/leixiaohua1020
*
* 本程序可以将封装格式中的视频码流数据和音频码流数据分离出来。
* 在该例子中， 将MPEG2TS的文件分离得到H.264视频码流文件和AAC
* 音频码流文件。
*
* This software split a media file (in Container such as
* MKV, FLV, AVI...) to video and audio bitstream.
* In this example, it demux a MPEG2TS file to H.264 bitstream
* and AAC bitstream.
*/
#include <stdio.h>
extern "C"
{
#include "libavformat/avformat.h"
};
/*
FIX: H.264 in some container format (FLV, MP4, MKV etc.) need
"h264_mp4toannexb" bitstream filter (BSF)
*Add SPS,PPS in front of IDR frame
*Add start code ("0,0,0,1") in front of NALU
H.264 in some container (MPEG2TS) don‘t need this BSF.
*/
//‘1‘: Use H.264 Bitstream Filter
#define USE_H264BSF 0
int main(int argc, char* argv[])
{
AVOutputFormat *ofmt_a = NULL,*ofmt_v = NULL;
//输入对应一个AVFormatContext，输出对应一个AVFormatContext
//（Input AVFormatContext and Output AVFormatContext）
AVFormatContext *ifmt_ctx = NULL, *ofmt_ctx_a = NULL, *ofmt_ctx_v = NULL;
AVPacket pkt;
int ret, i;
char *in_filename = "cuc_ieschool.ts";//输入文件名（Input file URL）
//char *in_filename = "cuc_ieschool.mkv";
char *out_filename_v = "cuc_ieschool.h264";//输出文件名（Output file URL）
//char *out_filename_a = "cuc_ieschool.mp3";
char *out_filename_a = "cuc_ieschool.aac";
av_register_all();
//输入（Input）
if ((ret = avformat_open_input(&ifmt_ctx, in_filename, 0, 0)) < 0) {
printf( "Could not open input file.");
goto end;
}
if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {
printf( "Failed to retrieve input stream information");
goto end;
}
//输出（Output）
avformat_alloc_output_context2(&ofmt_ctx_v, NULL, NULL, out_filename_v);
if (!ofmt_ctx_v) {
printf( "Could not create output context\n");
ret = AVERROR_UNKNOWN;
goto end;
}
ofmt_v = ofmt_ctx_v->oformat;
avformat_alloc_output_context2(&ofmt_ctx_a, NULL, NULL, out_filename_a);
if (!ofmt_ctx_a) {
printf( "Could not create output context\n");
ret = AVERROR_UNKNOWN;
goto end;
}
ofmt_a = ofmt_ctx_a->oformat;
int videoindex=-1,audioindex=-1;
for (i = 0; i < ifmt_ctx->nb_streams; i++) {
//根据输入流创建输出流（Create output AVStream according to input AVStream）
AVFormatContext *ofmt_ctx;
AVStream *in_stream = ifmt_ctx->streams[i];
AVStream *out_stream = NULL;
if(ifmt_ctx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO){
videoindex=i;
out_stream=avformat_new_stream(ofmt_ctx_v, in_stream->codec->codec);
ofmt_ctx=ofmt_ctx_v;
}else if(ifmt_ctx->streams[i]->codec->codec_type==AVMEDIA_TYPE_AUDIO){
audioindex=i;
out_stream=avformat_new_stream(ofmt_ctx_a, in_stream->codec->codec);
ofmt_ctx=ofmt_ctx_a;
}else{
break;
}
if (!out_stream) {
printf( "Failed allocating output stream\n");
ret = AVERROR_UNKNOWN;
goto end;
}
//复制AVCodecContext的设置（Copy the settings of AVCodecContext）
if (avcodec_copy_context(out_stream->codec, in_stream->codec) < 0) {
printf( "Failed to copy context from input to output stream codec context\n");
goto end;
}
out_stream->codec->codec_tag = 0;
if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
out_stream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;
}
//Dump Format------------------
printf("\nInput Video===========================\n");
av_dump_format(ifmt_ctx, 0, in_filename, 0);
printf("\nOutput Video==========================\n");
av_dump_format(ofmt_ctx_v, 0, out_filename_v, 1);
printf("\nOutput Audio==========================\n");
av_dump_format(ofmt_ctx_a, 0, out_filename_a, 1);
printf("\n======================================\n");
//打开输出文件（Open output file）
if (!(ofmt_v->flags & AVFMT_NOFILE)) {
if (avio_open(&ofmt_ctx_v->pb, out_filename_v, AVIO_FLAG_WRITE) < 0) {
printf( "Could not open output file ‘%s‘", out_filename_v);
goto end;
}
}
if (!(ofmt_a->flags & AVFMT_NOFILE)) {
if (avio_open(&ofmt_ctx_a->pb, out_filename_a, AVIO_FLAG_WRITE) < 0) {
printf( "Could not open output file ‘%s‘", out_filename_a);
goto end;
}
}
//写文件头（Write file header）
if (avformat_write_header(ofmt_ctx_v, NULL) < 0) {
printf( "Error occurred when opening video output file\n");
goto end;
}
if (avformat_write_header(ofmt_ctx_a, NULL) < 0) {
printf( "Error occurred when opening audio output file\n");
goto end;
}
#if USE_H264BSF
AVBitStreamFilterContext* h264bsfc = av_bitstream_filter_init("h264_mp4toannexb");
#endif
int frame_index=0;
while (1) {
AVFormatContext *ofmt_ctx;
AVStream *in_stream, *out_stream;
//获取一个AVPacket（Get an AVPacket）
if (av_read_frame(ifmt_ctx, &pkt) < 0)
break;
in_stream = ifmt_ctx->streams[pkt.stream_index];
if(pkt.stream_index==videoindex){
out_stream = ofmt_ctx_v->streams[0];
ofmt_ctx=ofmt_ctx_v;
printf("Write Video Packet. size:%d\tpts:%d\n",pkt.size,pkt.pts);
#if USE_H264BSF
av_bitstream_filter_filter(h264bsfc, in_stream->codec, NULL, &pkt.data, &pkt.size, pkt.data, pkt.size, 0);
#endif
}else if(pkt.stream_index==audioindex){
out_stream = ofmt_ctx_a->streams[0];
ofmt_ctx=ofmt_ctx_a;
printf("Write Audio Packet. size:%d\tpts:%d\n",pkt.size,pkt.pts);
}else{
continue;
}
/* copy packet */
//转换PTS/DTS（Convert PTS/DTS）
pkt.pts = av_rescale_q_rnd(pkt.pts, in_stream->time_base, out_stream->time_base, (AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
pkt.dts = av_rescale_q_rnd(pkt.dts, in_stream->time_base, out_stream->time_base, (AVRounding)(AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
pkt.duration = av_rescale_q(pkt.duration, in_stream->time_base, out_stream->time_base);
pkt.pos = -1;
pkt.stream_index=0;
//写入（Write）
if (av_interleaved_write_frame(ofmt_ctx, &pkt) < 0) {
printf( "Error muxing packet\n");
break;
}
//printf("Write %8d frames to output file\n",frame_index);
av_free_packet(&pkt);
frame_index++;
}
#if USE_H264BSF
av_bitstream_filter_close(h264bsfc);
#endif
//写文件尾（Write file trailer）
av_write_trailer(ofmt_ctx_a);
av_write_trailer(ofmt_ctx_v);
end:
avformat_close_input(&ifmt_ctx);
/* close output */
if (ofmt_ctx_a && !(ofmt_a->flags & AVFMT_NOFILE))
avio_close(ofmt_ctx_a->pb);
if (ofmt_ctx_v && !(ofmt_v->flags & AVFMT_NOFILE))
avio_close(ofmt_ctx_v->pb);
avformat_free_context(ofmt_ctx_a);
avformat_free_context(ofmt_ctx_v);
if (ret < 0 && ret != AVERROR_EOF) {
printf( "Error occurred.\n");
return -1;
}
return 0;
}
最简单的基于FFmpeg的封装格式处理：视音频分离器（demuxer）
原文：http://blog.csdn.net/leixiaohua1020/article/details/39802819