If your .mkv file already uses H.264 video (check with ffmpeg -i input.mkv ), you can "stream copy" it. This is instant and retains 100% quality, but might fail if the MKV contains subtitles or audio formats MP4 doesn't like.

Remember the "Interdimensional Cable" episodes? The whole joke is low-effort, chaotic, glitchy improv. That’s what a bad encode looks like. A bad encode introduces —blocky squares of color that appear during high-motion scenes (like the Die Hard episode’s explosion).

Some users use ffmpeg to rip the audio for listening on the go.

ffmpeg -i input.mkv -vf "yadif=1:0:0, deblock=alpha=1:beta=1" -c:v libx264 output.mkv

file 'Rick.and.Morty.S06E01.mkv' file 'Rick.and.Morty.S06E02.mkv' file 'Rick.and.Morty.S06E03.mkv'

FFmpeg does the same thing. It deconstructs the container format (MKV, MP4, AVI). It reconstructs the timecodes. It filters the reality of the video stream.

ffmpeg -i input.mkv -c:v libx264 -preset slow -crf 22 -c:a aac output.mp4