How to convert MKV to MP4 without re-encoding — ffmpeg remux

The video itself is fine, only the container is wrong — swapping it takes seconds and loses zero quality.

ffmpeg -i input.mkv -c copy output.mp4
# -c copy = copy streams as-is, no re-encoding

FFmpeg Cheatsheet one-page card — 28 commands that actually work — The full one-page card — FFmpeg Cheatsheet. Get the complete cheatsheet on GitHub