[Libav-user] Need help when muxing fragmented mp4 by using libavformat

[Dinh Nguyen]

Dear all,

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](https://github.com/codeaholicguy/mediasource-over-websocket) 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](https://drive.google.com/open?id=0B34Y_
mnzP99cMVlPMGpPQ2xfdmM)

 1. The first approach, I use ffmpeg to generate the [fragmented MP4 file](
https://drive.google.com/open?id=0B34Y_mnzP99cT21lWlV2VlpjOVU).

        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, and also can be streamed to web browser.

 2. The second approach, I programmaticaly generate the [fragmented Mp4
file by using libavformat](https://drive.google.com/open?id=0B34Y_
mnzP99cZHVRZjRmbmNoU0U)

    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?



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<https://vn.linkedin.com/in/nguyencatdinh>
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