Reverse.

Reversing a clip isn't a flag you can set on an encoder: video is compressed forwards, so playing it backwards means decoding every frame, holding it, and writing them out in the other order. Convert caches those frames to disk and rebuilds the clip from the end.

That's also why it stops at sixty seconds — a minute of frames is already a large amount of storage, and a cap you can see beats a conversion that dies two-thirds of the way through. Audio is dropped, because reversed sound is a joke with a very short shelf life.