Changing the actual speed of an AVI file is not simple because it requires that the file get re-encoded at a different frame rate. This will usually cause the video and audio to become out of sync, and may create other playback problems as well. A more practical solution is to adjust the speed at which the AVI file is played. This cuts down on audio/video synchronization problems and is much easier. Writer Bio

How to Speed Up an AVI File - 95