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All video playback on computers involves some form of video compression, typically embodied in products called codecs, which stands for COmpressor/DECompressor. Codec selection is of critical importance to the appearance of the finished video.
Microsoft's Video for Windows, the predominant development API on the Windows platform, ships with four video codecs, RLE from Microsoft, Video 1 from Microsoft and Media Vision, Cinepak from SuperMac and Indeo from Intel. RLE has little application for most digital videos, and will not be reviewed here.
In addition to Video for Window's (VFW) codecs, other codecs, written directly to Microsoft's Media Control Interface or MCI specification, are also available to Windows developers. One such example is Scalable MPEG from Xing Technologies.
COMPARISON CRITERIA
The measure of any codec is the ability to faithfully recreate the appearance of the original video. The two components of video quality are individual frame quality and playback rate.
* Individual Frame Quality. We will analyze two types of video, a talking head sequence and high motion sequence, to test the range of codec performance.
Most codecs use both interframe and intraframe compression. Interframe compression is compression achieved by eliminating interframe redundancy. Intraframe compression is compression achieved solely within an individual frame. Low motion talking head sequences and high motion action sequences represent the two ends of the interframe redundancy spectrum. For this reason, it is important to review both types of sequences when selecting a codec.
The two video sequences were captured in technology neutral RGB format. The videos are 320x240 in resolution and 15 frames/sec. They were all compressed to 150 Kbytes/sec, representing the bandwidth of a single speed CD-ROM drive.
* Playback Rate. Regardless of individual frame quality, if the codec can't decompress and display 10-15 frames/sec, overall quality suffers. Playback rates were calculated on a Gateway, 486/66 VL-bus with 8 Mbytes of RAM with an ATI Ultra Pro playing from a 150 Kbyte/sec CD-ROM.
OTHER CONSIDERATIONS
* Palette Management. Videos targeted towards 8-bit display platforms require special consideration to avoid "flashing," which occurs when a video's palette is different than the current display palette. Codecs handle palettes differently, and some are better suited than others for working with 8-bit displays.
* Smaller Video Sizes. Often producers will use smaller videos, such...