[Libav-user] Recomended approach for a timed metadata track within an mp4 (ISOBMFF section 12.3.3.2)

[Tom Vercauteren]

> Does this mean that muxing a KLV stream in an mp4 is not yet supported by
> libav or is there a workaround for this? If the former, would muxing a
> datastream with a different codec be supported in an mp4?
>
> It would be great if the muxing.c example could be expanded to include a
> data stream.
>

I have been making a bit of progress on this in the sense that I now have a
minimal working example with timed string-based metadata within a mov (or
ts file):
https://gist.github.com/tvercaut/890c9c78159189d685f9f9911a098278

Unfortunately, it doesn't work with mp4 files and I have had to a codec_tag
corresponding to gopro metadata: gpmd or rather MKTAG('g', 'p', 'm', 'd')
This came after reading this blog post:
https://coderunner.io/how-to-compress-gopro-movies-and-keep-metadata/
While they seem to be able to create an mp4 with the metadata, that hasn't
been my experience so far. Maybe that behaviour of ffmpeg changed with new
releases since the blog post? I see there is a related bug report here:
https://trac.ffmpeg.org/ticket/8338

If there is an alternative that would work with mp4 files (and ideally
without hacking the gopro metadata tag), I would be intersted to
investigate further.
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