FFmpeg 获取h264裸码流

有时候我们需要获取h264裸码流进行分析。本文介绍如何通过FFmpeg 获取h264 码流。获取到的h264码流文件 可以直接通过vlc 等播放器直接播放。

如下图 是通过WinHex工具 分析的一个h264文件

ffmpeg 获取h264 思路如下:

1，写4位头(00,00,00,01)

2，写sps

3，写4位头(00,00,00,01)

4，写pps

5，将读到的AVPacket.data 的前4位替换成（00,00,00,01）写文件。

sps pps的获取参考上篇博文。

详细代码如下:

int GetH264Stream()
{
	int ret;
	AVFormatContext *ic=NULL;
	AVFormatContext *oc=NULL;

	uint8_t sps[100];
	uint8_t pps[100];
	int spsLength=0;
	int ppsLength=0;
	uint8_t startcode[4]={00,00,00,01};
	FILE *fp;

	fp=fopen("123.h264","wb+"); 

	char *InputFileName="11111.mp4";

	if ((ret = avformat_open_input(&ic, InputFileName, NULL, NULL)) < 0)
	{
		return ret;
	}

	if ((ret = avformat_find_stream_info(ic, NULL)) < 0) 
	{  
		avformat_close_input(&ic);  
		return ret;  
	}  

	spsLength=ic->streams[0]->codec->extradata[6]*0xFF+ic->streams[0]->codec->extradata[7];

	ppsLength=ic->streams[0]->codec->extradata[8+spsLength+1]*0xFF+ic->streams[0]->codec->extradata[8+spsLength+2];

	for (int i=0;istreams[0]->codec->extradata[i+8];
	}
	
	for (int i=0;istreams[0]->codec->extradata[i+8+2+1+spsLength];
	}


	for(int i=0;inb_streams;i++)
	{ 
		if(ic->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO)
		{
			videoindex=i;
		}
		else if(ic->streams[i]->codec->codec_type==AVMEDIA_TYPE_AUDIO)
		{
			audioindex=i;
		}
	}

	AVOutputFormat *ofmt = NULL;
	AVPacket pkt;
	
	avformat_alloc_output_context2(&oc, NULL, NULL, OutPutPath);

	if (!oc) 
	{
		printf( "Could not create output context\n");
		ret = AVERROR_UNKNOWN;
	}
	ofmt = oc->oformat;
	int i;

	for (i = 0; i < ic->nb_streams; i++) 
	{
		AVStream *in_stream = ic->streams[i];
		AVStream *out_stream = avformat_new_stream(oc, in_stream->codec->codec);

		if (!out_stream) 
		{
			printf( "Failed allocating output stream\n");
			ret = AVERROR_UNKNOWN;
		}
		ret = avcodec_copy_context(out_stream->codec, in_stream->codec);
		if (ret < 0) 
		{
			printf( "Failed to copy context from input to output stream codec context\n");
		}
		out_stream->codec->codec_tag = 0;
		if (oc->oformat->flags & AVFMT_GLOBALHEADER)
			out_stream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;
	}

	if (!(ofmt->flags & AVFMT_NOFILE)) 
	{
		ret = avio_open(&oc->pb, OutPutPath, AVIO_FLAG_WRITE);
		if (ret < 0) 
		{
			printf( "Could not open output file '%s'", OutPutPath);

		}
	}
	ret = avformat_write_header(oc, NULL);

	int frame_index=0;
	int flag=1;

	av_init_packet(&pkt);
	pkt.data = NULL;
	pkt.size = 0;

	while (1) 
	{
		AVStream *in_stream, *out_stream;

		ret = av_read_frame(ic, &pkt);

		if (ret < 0)
			break;
		in_stream  = ic->streams[pkt.stream_index];
		out_stream = oc->streams[pkt.stream_index];

		AVPacket tmppkt;
		if (in_stream->codec->codec_type==AVMEDIA_TYPE_VIDEO )
		{

			if (flag)
			{
				fwrite(startcode,4,1,fp);
				fwrite(sps,spsLength,1,fp);
				fwrite(startcode,4,1,fp);
				fwrite(pps,ppsLength,1,fp);

				pkt.data[0]=0x00;
				pkt.data[1]=0x00;
				pkt.data[2]=0x00;
				pkt.data[3]=0x01;
				fwrite(pkt.data,pkt.size,1,fp);

				flag=0;
			}
			else
			{
				pkt.data[0]=0x00;
				pkt.data[1]=0x00;
				pkt.data[2]=0x00;
				pkt.data[3]=0x01;
				fwrite(pkt.data,pkt.size,1,fp);
			}

			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;
			ret = av_interleaved_write_frame(oc, &pkt);
		}

		av_free_packet(&pkt);
	}

	fclose(fp);
	fp=NULL;

	av_write_trailer(oc);
	return 0;
}