Fixes and Improvements for VTT subtitles support

Anyone of the developers have time to look into fixes and improvements needed for VTT subtitles support ?

  1. WebVTT subtitles work with external file, BUT not when embedded in the MKV.
    When embedded in the MKV - it doesn’t show at all (as an option to select) of the subtitles included in the MKV file. But the rest (SRT, ASS, PGS) inside the same file do show.
    I tried many different VTT files and remux with latest MKVToolNIX 51.0 - all with the same issue.

I FOUND A LEAD FOR A FIX:
FFmpeg (4.3.1) is showing vvt as:
“Stream #0:2: Subtitle: none ” when muxed into MKV.
And as:
“Stream #0:0: Subtitle: webvtt ” when stand-alone file.
Same issue also with latest FFmpeg from git (version git-2020-11-18-17a0dfe).
So it seems like an issue with FFmpeg ? Which I assume Infuse also use to some degree ?

  1. It seem the WebVTT support (as a stand-alone file , due to the above) disregard the WebVTT parameters. Like: “position”, “align”, “size” and “line”.
    These parameters are the only reason to use WebVTT in the first place (and not SRT for example).
    I assume ASS support does take into account parameters (like “position”) and it’s only an issue with WebVTT ?

Did any of the developers saw this ? Any thoughts ?