What is WEBM?
WebM is the web's own video container - Matroska slimmed down to the royalty-free codecs (VP8, VP9, AV1). Browsers play it natively and screen recorders love emitting it; the rest of the world's video tooling is distinctly lukewarm about it, which is why it so often needs converting.
What is AIFF?
AIFF is Apple's uncompressed audio format - WAV's counterpart from the Mac side of the world, and still what Logic and older Pro Tools sessions use. It stores its sample rate as an 80-bit extended float, a piece of 1980s exotica most converters get wrong.