[FFmpeg-trac] #10074(avformat:new): No metadata in adts container using libavformat API

[FFmpeg]

#10074: No metadata in adts container using libavformat API
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             Reporter:  Igor Serganov  |                     Type:  defect
               Status:  new            |                 Priority:  normal
            Component:  avformat       |                  Version:  5.1.2
             Keywords:                 |               Blocked By:
             Blocking:                 |  Reproduced by developer:  0
Analyzed by developer:  0              |
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 First of all I have to mention that I am not really sure if this is a bug,
 but probably more a help request.

 Background of the issue:

 I am doing live mp3 to aac transcoding with adts muxing. I am using C
 functions from libraries inside FFMPEG (libavcodec, libavformat, etc.)
 through CGO (a tool that allows call C code within Golang).

 Scenario is as follows:
 1. Open mp3 input
 2. Open output format:

 {{{
         adts := C.CString("adts")
         defer C.free(unsafe.Pointer(adts))
         var ctx *C.AVFormatContext
         if ret := C.avformat_alloc_output_context2(&ctx, nil,  adts, nil);
 ret < 0 {
                 return
         }
 }}}
 3. Write header with several options that I need for appropriate metadata
 (according to: https://datatracker.ietf.org/doc/html/rfc8216#section-3.4),
 options taken from here - https://ffmpeg.org/ffmpeg-formats.html#adts-1:


 {{{
 C.av_dict_set(&f.opts.dict, "write_id3v2","1", 0)
 C.av_dict_set(&f.opts.dict, "write_apetag","1", 0)
 C.av_dict_set(&outAVFormatCtx.metadata, "TIPL", "Awesome production", 0)
 C.avformat_write_header(&outAVFormatCtx, &f.opts.dict)
 }}}

 4. demuxing and decoding input stream and encoding frames and muxing to
 output stream. I will not provide too much details here as this part works
 pretty fine.

 5. Accumulating output stream of certain duration (10 seconds e.g.) and
 writing `.aac` segment to a storage. (Ideally this part works forever in
 order to produce HLS stream out of these segments later)

 6. When receiving a first frame for the following segment I try to write
 its PTS (start time of the next segment) to the metadata tag:


 {{{
 C.av_dict_set(&outAVFormatCtx.metadata,
 "PRIV.com.apple.streaming.transportStreamTimestamp", <some random int64
 value encoded to bytes>, 0)
 outAVFormatCtx.event_flags |= C.avfmt_event_flag_metadata_updated
 }}}

 However I don't see any metadata when ffprobing my segments:

     "format": {
         "filename": "filename.aac",
         "nb_streams": 1,
         "nb_programs": 0,
         "format_name": "aac",
         "format_long_name": "raw ADTS AAC (Advanced Audio Coding)",
         "duration": "10.011431",
         "size": "26458",
         "bit_rate": "38253",
         "probe_score": 51
     }

 However when I do something very similar with ffmpeg command as follows:

 ffmpeg -i input.mp3 -vn -acodec copy -f adts -metadata title="Foo"
 -metadata PRIV.com.apple.streaming.transportStreamTimestam="1111111"
 -write_id3v2 1 -write_apetag 1 output.aac

 I get what I want:

         "filename": "output.aac",
         "nb_streams": 1,
         "nb_programs": 0,
         "format_name": "aac",
         "format_long_name": "raw ADTS AAC (Advanced Audio Coding)",
         "duration": "5.485686",
         "size": "33278",
         "bit_rate": "48530",
         "probe_score": 51,
         "tags": {
             "TIT2": "Foo",
             "PRIV.com.apple.streaming.transportStreamTimestam": "1111111",
             "TSSE": "Lavf59.27.100"
         }


 So my question is how to write ID3v2 metadata to adts container through
 libavformat? Since this is quite a requirement of RFC-8216
 (https://datatracker.ietf.org/doc/html/rfc8216#section-3.4).
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/10074>
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