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AVI format Description
One of the oldest formats in the x86 computer world is AVI. The abbreviation ‘AVI’ stands for ‘Audio Video Interlaced’. This video format was created by Microsoft, which was introduced along with Windows 3.1. AVI, the proprietary format of Microsoft’s “Video for Windows” application, merely provides a framework for various compression algorithms such as Cinepak, Intel Indeo, Microsoft Video 1, Clear Video or IVI. In its first version, AVI supported a maximum resolution of 160 x 120 pixels with a refresh rate of 15 frames per second. The format attained widespread popularity, as the first video editing systems and software appeared that used AVI by default. Examples of such editing boards included Fast’s AV Master and Miro/Pinnacle’s DC10 to DC50. However, there were a number of restrictions: for example, an AVI video that had been processed using an AV Master could not be directly processed using an interface board from Miro/Pinnacle. The manufacturers adapted the open AVI format according to their own requirements.
AVI is subject to additional restrictions under Windows 95, which make professional work at higher resolutions more difficult. For example, the maximum file size under the FAT16 file system is 2 GB. The FAT32 file system (came with OSR2 and Windows 98) brought an improvement: in connection with the latest DirectX6 module ‘DirectShow’, files with a size of 8 GB can (at least in theory) be created. In practice however, many interface cards lack the corresponding driver support so that Windows NT 4.0 and NTFS are strongly recommended. Despite its age and numerous problems, the AVI format is still used in semi-professional video editing cards. Many TV cards and graphic boards with a video input also use the AVI format. These are able to grab video clips at low resolutions (mostly 320 x 240 pixels).
AVI is a file format, like MP3 or JPG. But unlike these formats, AVI is a container format, meaning it can contain video audio compressed using many different combinations of codecs. So while MP3 and JPG can only contain a certain kind of compression (MPEG Audio Layer 3 and JPEG), AVI can contain many different kinds of compression (eg. DivX video + WMA audio or Indeo video + PCM audio), as long as a codec is available for encoding/decoding. AVI all look the same on the “outside”, but on the “inside”, they may be completely different. Almost all tools on this site are not just DivX tools, but also AVI tools, so will probably work with other codecs. There is no such thing as a “normal” AVI file, but the closest you can get is probably an AVI file that contains no compression. AVI files has been around since the time of Windows 3.1, so by no means is it a new thing, and is probably the most common video format around (although its popularity wavered a few years ago, but has since come back with a vengeance due to the emergence of DivX). AVI files may also have limits under Windows 95/98, and for more information, please read this article. Note that AVI files without file limits (other than the Windows Fat32 file limit) are usually referred to as OpenDML AVI files.