There are a lot of contradicting information about AVI and MPEG4 on the discussion groups. Let's clear up once and for all what is AVI, what is DivX and what is MPEG4.
AVI is a container. AVI means Audio Video Interleave. AVI contains only information that describes how to store the data in file and how to decompress the video and the audio (which codecs to use for these purposes).
DivX is a codec, a video compressor and decompressor. Video data can be compressed with DivX codec and stored inside AVI files.
Also, CinePak, Indeo, Huffyuv and other video codecs can be used to create AVI files.
Typical AVI: the Video compressed with DivX or XviD or Cinepak, and the Audio compressed with MP3 or ADPCM, or just plain PCM.
In other words, the universal AVI container allows to use many combinations of codecs (encoders/decoders) for storing the video/audio data.
MPEG-4 is not a codec, and it is not a container.
MPEG-4 is a name of collection of methods defining compression of audio and visual (AV) digital data. Related technology agreed upon by the ISO/IEC Moving Picture Experts Group (MPEG) under the format standard ISO/IEC 14496.
Methods described in MPEG-4 part 2 (MPEG-4 SP/ASP) are used by codecs such as DivX, Xvid, Nero Digital, 3ivx and by Quicktime, and methods described in MPEG-4 part 10 (MPEG-4 AVC/H.264) are used by the x264 codec, by Nero Digital AVC and by the high-definition DVD formats like HD DVD and Blu-ray Disc.