[Question] Recommended means of multiplexing GPMF data in an mp4

[tvercaut]

Thanks for the nice project. I am interested in storing timed metadata alongside video data in a fragmented mp4 file (fragmentation is for tolerance to sudden failure during encoding, say running out of disk space or software crash). GPMF looks great for the metadata side.

While I understand from the README and a previously closed issue (#1) that robust multiplexing of GPMF data in an mp4 is out of scope for this library, I would be interested to learn what the recommended way of doing so would be.

I looked at ffmpeg / libav so far but haven't managed to create a data track in an mp4 with it yet. The closest I got is to do it in a mov file (I haven't started the GPMF part not the fragmentation part yet):
https://gist.github.com/tvercaut/890c9c78159189d685f9f9911a098278
See also a related email thread here: http://ffmpeg.org/pipermail/libav-user/2022-March/013041.html and http://ffmpeg.org/pipermail/libav-user/2022-April/013043.html

Given the ffmpeg bug report below, I am wondering if ffmpeg / libav is a viable option for my need:
https://trac.ffmpeg.org/ticket/8338

I have been looking at other options but haven't found something ideal yet. I have seen the following:

• libmp4 doesn't seem to support fragmented mp4s: https://github.com/Parrot-Developers/libmp4 (note that this seem to be designed for an alternative metadata format as per https://github.com/Parrot-Developers/libvideo-metadata and https://developer.parrot.com/docs/pdraw/video-metadata.html )
• bento4 is GPL licensed and thus too restrictive for me: https://github.com/axiomatic-systems/Bento4
• media-server/libmov may be suitable but it is under-documented with no simple examples to start from https://github.com/ireader/media-server