Convert Dolby Vision to MKV

[alan]

Quick try:
[mp4 @ 000002a126b00d80] track 1: codec frame size is not set
[mp4 @ 000002a126b00d80] track 2: codec frame size is not set
[mp4 @ 000002a126b00d80] Could not find tag for codec subrip in stream #3, codec not currently supported in container
[out#0/mp4 @ 000002a125004ec0] Could not write header (incorrect codec parameters ?): Invalid argument
Error opening output file my_movie.mp4.
Error opening output files: Invalid argument

Using ffmpeg from JF. ffmpeg version N-111510-gbe7ac511a6-20230719.

I'm sure ffmpeg can do it but just not getting 'there' yet. I'll dig further tommorrow.