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AVI format

Most of our readers know what AVI format is, but there are something about it that you may don’t know. AVI will be adressed by the following parts: history and basics, codecs, drawbacks, and myths about it.

History and basics.  AVI is one of the oldest video formats still in common use, having been created by Microsoft more than a decade ago. An AVI is an Audio-Video Interleave based on RIFF headers (resource interchange file format). For years, it was the only viable digital video format available.

Codecs. An AVI is actually not a video format. The “AVI” file is merely a wrapper, what I like to call a “container” file. It holds video and audio information that would typically be unable to exist as its own file format. This video and audio information is written to and read from the AVI by codecs (compressor-decompressor files). Popular codecs include MPEG-4, DivX, Xvid, MJPEG, HuffYUV, and other FourCC variations. Even MPEG and Windows Media Video (WMV) can exist within an AVI file, as the AVI is just video data with a RIFF header surrounding it.

Temporary only. Most AVI codecs are intended only as temporary working format, not meant to be final products. An AVI typically serves no purpose outside of an editing environment on a computer using Windows. It has little compression applied, and can easily be manipulated a few times before degradation occurs to the video information. This is opposite of television/DVD formats like MPEG, and streaming formats like QuickTime, RealMedia and WMV, all of which are end-product formats. Apple uses Sorenson-based QT files as their working format.

Drawbacks. The AVI format has several distinct drawbacks, with the major one being huge file sizes when using no- or low-compression codecs. (Older variations of AVI present in Windows 3.x and Windows 95/98/NT4 had limitations that prevented file size of larger than 2GB or 4GB, however that has since been removed with the newer operating systems and updates for 98/NT4.)

Myths. An AVI is not any better than an MPEG. It is just different. In fact, using a low bit-rate DivX codec AVI encode will always look worse than a high bit-rate MPEG. Quality depends on how you use the files. As has been stated earlier in this section, if editing is not needed, then capturing directly to MPEG is acceptable and quality will be just fine, assuming the capture card and capture program are decent. This is why most people assume MPEG is worse: their hardware and software is not great. Be aware that many of the so-called “lossless” codecs are still quite lossy.

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