The source project of this merge request has been removed.
Update file_types.cpp: webvtt, weba, f4v
WebVTT: Some programs output WebVTT subtitles with the file extension .webvtt (gMKVExtractGUI for example)
WebA: Some programs output a .weba file for OPUS in WebM container (it is also mentioned on matroska.org)
F4V: https://filesamples.com/formats/f4v MKVToolNix can successfully remux f4v