Lossless trim: why a cut should make the file smaller

Decoding a video to raw frames, cutting, and encoding again is the obvious algorithm. It is also slow and it changes the picture. The other algorithm copies the compressed packets that already exist and writes a new index.

That is what Trim Video and Trim Audio do when the codec allows it. The output cannot be larger than the input. Cuts land on a keyframe, usually within a second of the time you typed.

Effects — fade, speed, a title — must decode. Use them after you have the range you want, not instead of a lossless cut.