Files like "534783.mkv" are typically generated using tools such as MakeMKV , a "transcoder" that converts video from proprietary, encrypted discs into the MKV format.
It can store multiple audio tracks (e.g., different languages or director commentaries) and complex subtitle formats. 534783.mkv
Using tools like FFmpeg or Subler to change the container (e.g., to .mp4) without re-encoding the video. Files like "534783