Audio Video Interleave. A simplistic Resource Interchange File Format
based, media container format
defined by Microsoft
and used as the native file format
of its Video for Windows
software since the early 1990s.
Synchronization between the audio and the video can often be poor as standard AVIs include no real timing method. The format does allow optionally interleaving the video and audio streams, which can help synchronization problems.
Since AVI is only a container format the actual codec used for compression of the video and audio can vary, but Indeo, Cinepak, and RLE are common for video. For audio PCM is common.
AVI was eventually extended with features for professional video production by the Open Digital Media Consortium. Their changes include removal of a 2 gibibyte file size limit, and adding timecodes for dependable audio to video synchronization. Microsoft has supported these extensions in their Video for Windows, and Windows Media Player software.
There is one interesting feature inherent in AVIs which has interesting effects for internet file sharing: the (optional) index that lets a video player seek to random points quickly is located at the very end of the file. This means that any incomplete download will take significantly longer to seek within.
In 1998 Microsoft released the ASF (originally Active, now Advanced Streaming Format) specification codeveloped with Real Networks. This was intended as the successor to AVI, however the AVI format is still being used as a container for newer codecs, including the very popular DivX, OpenDivX, XviD family of encoders.