What is MOV?

QuickTime, and what a Mac or an iPhone records into. Structurally it's almost the same file as an MP4 - both grew from the same specification - but plenty of software sees the extension and refuses anyway, which is the entire reason MOV to MP4 is a conversion people need.

What is MP3?

The format that made digital music portable, and thirty years on it's still the safest bet that a file will simply play - any device, any car, any decade-old bit of hardware. It's lossy, its patents expired in 2017, and no browser has ever been able to write one, which is why encoding it here needs LAME.