如何使用H264编解码器编写带有libavcodec for MP4文件的avc1 atom

Question

av_write_frame(outputFormatCtx, &pkt);

这是我到目前为止的努力，在从返回的编码器缓冲区解析SP和pps之后。（在memcping到sps和pps之前，我删除了前导的0x0000001 nal分隔符）。

 if ((sps) && (pps)) {
          //length of extradata is 6 bytes + 2 bytes for spslen + sps + 1 byte number of pps + 2 bytes for ppslen + pps

          uint32_t extradata_len = 8 + spslen + 1 + 2 + ppslen;
          outputStream->codecpar->extradata = (uint8_t*)av_mallocz(extradata_len);

          outputStream->codecpar->extradata_size = extradata_len;

          //start writing avcc extradata
          outputStream->codecpar->extradata[0] = 0x01;      //version
          outputStream->codecpar->extradata[1] = sps[1];    //profile
          outputStream->codecpar->extradata[2] = sps[2];    //comatibility
          outputStream->codecpar->extradata[3] = sps[3];    //level
          outputStream->codecpar->extradata[4] = 0xFC | 3;  // reserved (6 bits), NALU length size - 1 (2 bits) which is 3
          outputStream->codecpar->extradata[5] = 0xE0 | 1;  // reserved (3 bits), num of SPS (5 bits) which is 1 sps

          //write sps length
          memcpy(&outputStream->codecpar->extradata[6],&spslen,2);

          //Check to see if written correctly
          uint16_t *cspslen=(uint16_t *)&outputStream->codecpar->extradata[6];
          fprintf(stderr,"SPS length Wrote %d and read %d \n",spslen,*cspslen);


          //Write the actual sps
          int i = 0;
          for (i=0; i<spslen; i++) {
            outputStream->codecpar->extradata[8 + i] = sps[i];
          }

          for (size_t i = 0; i != outputStream->codecpar->extradata_size; ++i)
                fprintf(stderr, "\\%02x", (unsigned char)outputStream->codecpar->extradata[i]);
                fprintf(stderr,"\n");

          //Number of pps
          outputStream->codecpar->extradata[8 + spslen] = 0x01;

          //Size of pps
          memcpy(&outputStream->codecpar->extradata[8+spslen+1],&ppslen,2);

          for (size_t i = 0; i != outputStream->codecpar->extradata_size; ++i)
                fprintf(stderr, "\\%02x", (unsigned char)outputStream->codecpar->extradata[i]);
                fprintf(stderr,"\n");

          //Check to see if written correctly
          uint16_t *cppslen=(uint16_t *)&outputStream->codecpar->extradata[+8+spslen+1];
          fprintf(stderr,"PPS length Wrote %d and read %d \n",ppslen,*cppslen);


          //Write actual PPS
          for (i=0; i<ppslen; i++) {
           outputStream->codecpar->extradata[8 + spslen + 1 + 2 + i] = pps[i];
          }

          //Output the extradata to check
          for (size_t i = 0; i != outputStream->codecpar->extradata_size; ++i)
                fprintf(stderr, "\\%02x", (unsigned char)outputStream->codecpar->extradata[i]);
                fprintf(stderr,"\n");


          //Access the outputFormatCtx internal AVCodecContext and copy the codecpar to it
          AVCodecContext *avctx= outputFormatCtx->streams[0]->codec;

          fprintf(stderr,"Extradata size output stream sps pps %d\n",outputStream->codecpar->extradata_size);
          if(avcodec_parameters_to_context(avctx, outputStream->codecpar) < 0 ){
             fprintf(stderr,"Error avcodec_parameters_to_context");

          }

          //Check to see if extradata was actually transferred to OutputformatCtx internal AVCodecContext
          fprintf(stderr,"Extradata size after sps pps %d\n",avctx->extradata_size);



          //Write the MP4 header
          if(avformat_write_header(outputFormatCtx , NULL) < 0){
            fprintf(stderr,"Error avformat_write_header");
            ret = 1;
          } else {
            extradata_written=true;
            fprintf(stderr,"EXTRADATA written\n");
          }    
       } 

生成的视频文件将不播放。该extradata实际上存储在MP4文件的尾部部分，而不是AVC1的MP4头中的位置。因此它是由libavcodec编写的，但很可能是由avformat_write_trailer编写的。

我将在这里发布PPS和SPS信息以及最终的extradata字节字符串，以防在形成extradata时出错。

下面是硬件编码器的缓冲区，其前缀为nal分隔符的sps和pps

\00\00\00\01\27\64\00\28\AC\2B\40\A0\CD\00\F1\22\6A\00\00\00\01\28\EE\04\F2\C0

以下是13字节SPS：

27640028ac2b40a0cd00f1226a

下面是5字节PPS：

28ee04f2c0

下面是最后一个extradata字节字符串，它是29个字节长。我希望我写的PPS和SPS大小正确。

\01\64\00\28\FF\E1\0D\00\27\64\00\28\AC\2B\40\A0\CD\00\F1\22\6A\01\05\00\28\EE\04\F2\C0

我对编码器的后继帧进行了相同的转换，从NAL分隔符0x0000001转换为4字节NAL大小，并将它们按顺序保存到文件中，然后编写拖车。

知道错在哪里吗？我怎样才能写的引渡到它的适当位置在MP4头？

谢谢，克里斯

Answer 1

我发现了问题所在。raspberry pi是小endpoint，所以我假设我必须用小endpoint写sps长度和pps长度以及每个NALU大小。它们需要用大端语来写。在我做了更改之后，mp4info和mplayer中显示的avcc atom现在可以回放视频了。不必访问outputformatctx内部avcodeccontext并修改它。

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