No Upload Studio
Fix a video that plays sideways or upside down, or mirror it. The turn is saved into the picture itself, so it plays the right way up everywhere, and the video stays on your device.
Phones often store a video sideways with a note saying "turn this when you play it", and some players ignore the note. When the editor saves at a quality like Maximum, the turn goes into the picture itself, so the MP4 is upright in every player. Lossless (cuts only) copies the video as it is, note included.
No, only in 90° steps. That's what you need for videos filmed with the phone held the wrong way.
The picture is encoded again, because it changes. Maximum quality, the default, aims to look the same as your original.