Different between fragmented mp4 files generated by ffmpeg and by code

Question

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

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

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?

h264 file: drive.google.com/open?id=0B34Y_mnzP99cMVlPMGpPQ2xfdmM , ffmpeg generated mp4 file: drive.google.com/open?id=0B34Y_mnzP99cT21lWlV2VlpjOVU , libavformat generated mp4 file: drive.google.com/open?id=0B34Y_mnzP99cZHVRZjRmbmNoU0U — dinhnguyen

reborn reborn · Accepted Answer · 2021-05-13T08:06:34

Maybe you can try this:

AVDictionary* opts = NULL;
av_dict_set(&opts, "movflags", "frag_keyframe+empty_moov", 0);

And then:

avformat_write_header(formatContext, &opts);

As this qusetion How to generate fragmented mp4 files programmatically

Different between fragmented mp4 files generated by ffmpeg and by code

1 Answers