[quietvoid]

Implements #417

[JiiPee74]

Just want to leave here some information if someone happens to wonder.

I am working on script what parse different information from .mkv and it started to bother me that I cannot use dovi_tool directly to parse information from old dual track dovi .mkv files. So now it is possible, dont need to feed through ffmpeg first. :)

When parsing thouse old dual tracks, do not use '--limit 1', it does not work because it cannot find nalu 62 from track 2, frame 1.
Reason is unclear to me. It might be that old mkvmerge did add some garbage to second track, because if you extract track and do extract-rpu agaisnt raw hevc you can use '--limit 1'.
However if you extract whole rpu it is identical to rpu extracted from raw hevc track.

Its just that my use case it to get snap from rpu and then turn it to json to see frame information.

After all thank you for implementing this. :)