I am trying to create a web application where users generate movies. They make the movies out of images and mp3's they upload.
The final result must be a movie file eg mp4/mov or avi.
In order to do this, I need a php library that creates movie from these sources.
Does anyone know of one?
Yes you can, You should use ffmpeg or mencoder.
see this for example : http://electron.mit.edu/~gsteele/ffmpeg/