I saw a file the other night with an .mp4 extension. What codec is needed to play it? Defiler did not seem to be up to the job. I thought .mp4 was an audio format not a movie format but google says ...

What's the difference? If I rip a DVD or transcode a file, say avi, to mpeg4 using visualhub, I'll get an mp4 out of the other end. But when I use the conversion option in EyeTV's software, a ...