Though it is not primarily designed for this purpose, Nero Vision (a program included in Nero Burning ROM) can easily be used to convert a computer video file from one format to the next. Nero Vision has a sub-function that acts as a standard video file editor (like Final Cut Pro or Adobe Premiere), so if you want to convert an MP4 file to the AVI file format you would just import it as an MP4, then export it as an AVI.
