Tools like MKVToolNix are used to edit, merge, or remove tracks from MKV files without re-encoding.

Supports embedded fonts, custom styles, and chapters for easier navigation.

If the file is not supported by a device, it can be "remuxed" (copied without re-encoding) into an MP4 container using tools like Xmedia Recode or Avidemux .

Do you know the of the file (e.g., a Blu-ray rip, a recording)?