Audio-video interleave (AVI) is a popular personal computer (PC) multimedia file formatting standard that combines audio and video into one file. Introduced by Microsoft® in the early 1990s, AVI is meant for playback on a PC media player. In addition to the audio and video file information, these types of files contain information that tells the computer how to decode the audio and video data. For this kind of file to play on a computer media player, the player needs to be equipped with compatible codecs that allow the player to decode and play back the encoded media in the file.
In an AVI file, information embedded in a four-character code (FOURCC) tells the computer which type of software codec to use. A codec is a computer program or plug-in that decodes a file. AVI-compatible codecs include the DivX codec™, the Cinepak™ codec, the Indeo™ codec, and the digital video (DV) codec, but not all codecs will work with every file of this type. Though a file is built in the AVI standard, it can be created using different, incompatible types of encoding, each of which needs a specific software codec in order to decode the data and play the file. Companies that make software media players or media codecs often offer codec installation files for download directly from their company websites.
The structure behind this type of media file is designed from file type architecture originally used in the Resource Interchange File Format (RIFF). RIFF format organizes data into information chunks, each bearing its own FOURCC-type code designed to outline file information for the RIFF chunk. An AVI file is essentially one RIFF chunk with one set of FOURCC encoding information. The RIFF file format was also introduced by Microsoft®. Other file types based on the structure used in RIFF include audio files (WAV) and animated cursor graphics files (ANI).
Though AVI is the most popular video file type used on PC, some media players experience playback problems with this type of file format. Some video playback software may not be able to automatically select the correct video aspect ratio, so the user may need to adjust to the correct aspect ratio using the program's manual controls. Other problems with this media standard include difficulties encoding audible sound with MPEG-1 Audio Layer 3 (mp3) audio that has been encoded at low quality sample rates. MPEG-1 is a standard of audio and video compression set by the Motion Picture Experts Group (MPEG).
