Whatever the recording, audio just wants to be heard: the trick is picking a shape that plays where you need it. It was born in wherever your microphone, DAW or download came from, and its real weak spot is nothing in particular; the limits belong to whichever format it happens to be wearing.
FLV is a relic of the Flash era: the format YouTube grew up on, stranded when Flash died. The Flash Video container, typically holding old H.263, VP6 or early H.264 streams. That makes it the right destination when what you need is nothing new: today it's mostly old downloads waiting to be rescued.