Different between fragmented mp4 files generated by ffmpeg and by code

问题

Currently I have a problem when generating fragmented MP4 file from code using libavformat. My file can be played using VLC, but can't be streamed (via WebSocket) and played (via MediaSource) in (Chrome) browser. (I used this to test streaming fragmented MP4 file to browser via WebSocket).

Note: The files below is encoded by Baseline profile, level 4. So you should change the MIME type (in index.html) to const mimeCodec = 'video/mp4; codecs="avc1.42C028"'; to be able to play them.

I checked and found that my generated Mp4 file is a bit different with the file generated by using ffmpeg tool.

Here's what I've done:

I have a .h264 file

1. The first approach, I use ffmpeg to generate the fragmented MP4 file.

   ffmpeg -i temp.h264 -vcodec copy -f mp4 -movflags empty_moov+default_base_moof+frag_keyframe ffmpeg.mp4
   

   The generated file can be played by both Quicktime player and VLC player

2. The second approach, I programmaticaly generate the fragmented Mp4 file by using libavformat

   First I initialize the context, the codec in code is the AVCodecContext* of the input stream

    av_register_all();
    avcodec_register_all();
    int ret;
    AVOutputFormat* fmt = av_guess_format("mp4", 0, 0);
    if(!fmt) {
      return;
    }
   
    AVFormatContext* ctx = avformat_alloc_context();
    // Create AVIO context to capture generated Mp4 contain
    uint8_t *avio_ctx_buffer = NULL;
    size_t avio_ctx_buffer_size = 50000;
    IOOutput buffer = {};
    const size_t bd_buf_size = 50000;
    avio_ctx_buffer = (uint8_t*)av_malloc(avio_ctx_buffer_size);
    buffer.buff = (uint8_t*)av_malloc(bd_buf_size);
   
    buffer.size = bd_buf_size;
    AVIOContext* ioCtx = avio_alloc_context(avio_ctx_buffer, (int)avio_ctx_buffer_size, 1, &buffer, NULL, MP4Formatter::onWritePacket, NULL);
   
    ctx->oformat = fmt;
    if (ctx->oformat->flags & AVFMT_GLOBALHEADER)
      ctx->flags |= CODEC_FLAG_GLOBAL_HEADER;
    ctx->pb = ioCtx;
    av_opt_set(ctx, "movflags", "frag_keyframe+empty_moov+default_base_moof", 0);
   
    AVStream* st = avformat_new_stream(ctx, codec->codec);
    if (!st) {
      return;
    }
   
    st->id = (ctx->nb_streams - 1);
    avcodec_parameters_from_context(st->codecpar, codec);
    st->time_base = codec->time_base;
    ioCtx->seekable = false;
   

   Second I implement the onWritePacket callback

    int MP4Formatter::onWritePacket(void *opaque, uint8_t* buf, int buf_size) {
      file.write((char*)buf, buf_size);
    }
   

   Third, on every packet from h264 file, I write it using av_interleaved_write_frame

    if (firstFrame) {
      AVDictionary *opts = NULL;
      av_dict_set(&opts, "movflags", "frag_keyframe+empty_moov+default_base_moof", 0);
      if(!parseSPSPPS(data, length)) {
        return;
      }
      cout << "spslen " << spslen << " ppslen " << ppslen << endl;
      auto c = st->codecpar;
      // Extradata contains PPS & SPS for AVCC format
      int extradata_len = 8 + spslen + 1 + 2 + ppslen;
      c->extradata = (uint8_t*)av_mallocz(extradata_len);
      c->extradata_size = extradata_len;
      c->extradata[0] = 0x01;
      c->extradata[1] = sps[1];
      c->extradata[2] = sps[2];
      c->extradata[3] = sps[3];
      c->extradata[4] = 0xFC | 3;
      c->extradata[5] = 0xE0 | 1;
      int tmp = spslen;
      c->extradata[6] = (tmp >> 8) & 0x00ff;
      c->extradata[7] = tmp & 0x00ff;
      int i = 0;
      for (i=0; i<tmp; i++) {
        c->extradata[8 + i] = sps[i];
      }
      c->extradata[8 + tmp] = 0x01;
      int tmp2 = ppslen;
      c->extradata[8 + tmp + 1] = (tmp2 >> 8) & 0x00ff;
      c->extradata[8 + tmp + 2] = tmp2 & 0x00ff;
      for (i=0; i<tmp2; i++) {
        c->extradata[8 + tmp + 3 + i] = pps[i];
      }
      int ret = avformat_write_header(ctx, &opts);
      if(ret < 0) {
        return;
      }
      firstFrame = false;
    }
    AVPacket pkt;
    av_init_packet(&pkt);
    pkt.buf = av_buffer_alloc(length);
    memcpy(pkt.buf->data, data, length);
    pkt.buf->size = length;
    pkt.data = pkt.buf->data;
    pkt.size = pkt.buf->size;
    pkt.pts = ts;
    pkt.dts = ts;
   
    if (keyFrame) {
      pkt.flags |= AV_PKT_FLAG_KEY;
    }
    else {
      pkt.flags = 0;
    }
   
    pkt.stream_index = st->id;
   
    av_interleaved_write_frame(ctx, &pkt);
    av_buffer_unref(&pkt.buf);
    av_packet_unref(&pkt);
   

Can you guys take a look at my file to see what's wrong?

来源：https://stackoverflow.com/questions/42430809/different-between-fragmented-mp4-files-generated-by-ffmpeg-and-by-code