I need to change the playback speed of a video, but can't use mencoder to do it. Changing the speed that a video plays at seems like the sort've thing that any video encoding software should be able to do, but mencoder is the only one that I've seen with a built-in option. Mencoder is also the only one that I've seen that does it fast. There are examples on the web of changing the speed with ffmpeg by converting to raw video frames and then putting them back together, but mencoder is clearly doing something faster because speed changes happen in nearly the time it takes to simply copy the file.
Does anyone know how mencoder is changing the playback speed with the