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。

流程图

代码

/**
 * 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;
}

结果

下载

最简单的基于FFmpeg的封装格式处理：视音频分离器（demuxer）