Microsoft Video for Windows
Video for Windows was Microsoft's first attempt to compete with QuickTime. However, the original AVI was a much less sophisticated format. Although like QuickTime - in that it can act as a wrapper for different audio and video codecs - it doesn't have the track-based structure. Instead, audio and video are interleaved (which is what the AVI file extension actually stands for), so there's no option for any other media types to be embedded.
However, many of the specific codecs we'll be discussing later in this article and next week are available with a Video for Windows wrapper. The format is readily extensible with third-party additions. The list of possibilities is therefore huge. The latest standard line-up includes three different versions of Indeo, Cinepak and the venerable Video 1, but there's also a standard Microsoft version of DV with a special AVI file type all of its own. Windows Media Video 9, various manufacturer-specific versions of DV, M-JPEG, and numerous flavours of MPEG-4 can be added, too, the most popular being DivX.
DirectShow is an evolution of Video for Windows into the world of DirectX. It's essentially another container above Video for Windows. Advanced Systems Format (ASF, which includes WMV and WMA), MPEG, MP3 and WAV files can all be handled by DirectShow, as well as AVIs. Source files are parsed into their separate video and audio streams, which are then sent to their respective decoders. So DirectShow is essentially Microsoft's direct answer to QuickTime, where the AVI was a video-only imitation.
Now we've covered the two main container formats, let's finish off this week's article with a look at the two main intraframe editing codecs you are likely to come across.