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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;i<spsLength;i++){sps[i]=ic->streams[0]->codec->extradata[i+8];}for (int i=0;i<ppsLength;i++){pps[i]=ic->streams[0]->codec->extradata[i+8+2+1+spsLength];}for(int i=0;i<ic->nb_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;}

我诚恳地希望能够获得你的原谅。只是你懂得的，对于有一些委屈，