MKV supports this metadata, and a MKV video file that has this metadata plays correctly (as 360° video) in VLC.
I tested it by converting a MP4 file (that I had injected the metadata into) to MKV using ffmpeg.
ffmpeg -i 360.mp4 -c:v ffv1 -level 3 -threads 8 -coder 1 -context 1 -g 1 -slices 24 -slicecrc 1 -c:a flac 360_ffv1.mkv
It played correctly in VLC.
But it would be nicer if it would be possible to directly inject it into mkv files, because
it would be more convenient to not have to create a mp4 file first and
this conversion from mp4 to mkv only works for codecs that mp4 supports.
But there are codecs (like the lossless FFV1 codec) that only MKV supports!
MKV supports this metadata, and a MKV video file that has this metadata plays correctly (as 360° video) in VLC. I tested it by converting a MP4 file (that I had injected the metadata into) to MKV using ffmpeg.
ffmpeg -i 360.mp4 -c:v ffv1 -level 3 -threads 8 -coder 1 -context 1 -g 1 -slices 24 -slicecrc 1 -c:a flac 360_ffv1.mkvIt played correctly in VLC. But it would be nicer if it would be possible to directly inject it into mkv files, because