Support for .vtt subtitles embedded in .mp4 file
VLC 3.0.20 opens WebVTT files, but does not support these subtitles when embedded in an mp4 container. I use mp4box to embed subtitles:
mp4box.exe -add "video.264#video:name=" -add "audio.aac#audio:group=1:name=" -add "WebVTT.vtt:hdlr=text:stype=wvtt:group=2:disable:name=" -itags reset -tmp tmp -new wvtt.mp4
I made a test .mp4 file with such subtitles (wvtt.mp4): https://github.com/zablockil/srt_vtt_mp4/tree/main/VLC