Better compression but slower:

ffmpeg -i "Young.Sheldon.S03E05.mkv" \ -c:v libx264 -crf 23 -preset medium \ -c:a aac -b:a 128k \ "Young.Sheldon.S03E05.mp4"

The piece played (and hummed) in the episode is (specifically the Russian version ).

Change container without re-encoding (e.g., MKV → MP4):

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