AVI = Audio Video Interleave
MPEG4 = a type of AVI file, typically associated with DivX, XviD which are both MPEG4-codecs
The "difference" is that AVI is a container. It's not a coder/decoder. AVI contains only information that describes how the data is included in file and how to decompress video and audio (which codec to use). MPEG4 - is a compressor. Video data can be compressed with MPEG-4. AVI can have any type of codec (or no codec even) for compression, CinePak, Indeo, Huffyuv, etc whilst a "MPEG4 'file'" specifically denotes any AVI file that uses an MPEG4 codec (i.e,, DivX)
AVI may have MPEG-4 as Video, and MP3 as Audio.
AVI may have Cinepak as Video, and WAV PCM as Audio.
Many codecs for only one universal AVI container.
Last update: 07:20 PM Sunday, February 26, 2006