MKV is extremely flexible
Matroska can carry many video, audio and subtitle codecs. That flexibility is why MKV-to-MP4 is not just an extension rename.
Track preservation matters
A useful converter tells you which tracks survive. OpenFileTools surfaces conversion validity and discarded-track reasons rather than hiding them.
MP4 has stricter practical combinations
A broad-delivery MP4 usually needs a compatible video/audio pair. Unsupported codecs require transcoding when the browser can decode them.
Keep the original when it contains extras
Attachments, multiple subtitles or uncommon audio can be useful even if the MP4 destination does not preserve them. Keep the MKV master.
Official marketplace references
Requirements can change. Review the source before publishing an important listing.
Mediabunny browser media toolkit documentation ↗