Both Quicktime for Windows and Video for Windows are designed with open codec architectures. The form of the algorithm used to compress a video sequence is specified in the digital video data file format. On identifying the codec, the video software loads the appropriate driver to decompress the data. This can include codecs which use hardware boards to speed processing as well as algorithms implemented solely in software.
For CD-ROM applications, codecs that can decompress video without any special hardware are attractive because the potential audience is large. That is why most video on CD-ROM is compressed using either SuperMac's Cinepak or Intel's Indeo. These codecs can achieve a full 30 frame per second rate for 160 X 120-pixel 16-bit color pictures and 15 frames per second at 320 X 240.
But choice of a codec is more than a battle between Cinepak and Indeo. The industry standard for compressing movies, MPEG is now moving into the marketplace. MPEG I, the codec designed for CD-ROMs can achieve 30 fps on 320 X 240 windows when played back on boards that cost less than $500.
The key question is whether developers should move to MPEG I or stick with software. Most people agree that MPEG I playback looks better and it has the added advantage of compressing audio. However, faster CPUs and buses on multimedia PCs and low-cost general-purpose video acceleration cards may save software codecs from being replaced by MPEG. On fast Pentium and Power PCs, Cinepak and Indeo can achieve 30 fps at 320 X 240. They can be blown up to 640 X 480 using new graphics accelerators. The quality is not quite as good as MPEG but close and they are a lot cheaper for encoding and playback.
To make matters more complicated, there are a number of mature, established codecs such as Motion-JPEG and DVI as well as some new up-and-coming technologies such as fractals and wavelets to choose from.
There are primarily three criteria involved in selecting a codec:
The following chart gives a summary of your video codec choices:
Platform S/W Playback Playback Size/Rate
Captain Crunch Media Vision Wavelet PC No 320 X 240 @ 30fps
Cinepak SuperMac VQ Mac, PC Yes 320 X 240 @ 15fps
DVI-RTL Intel VQ PC No 256 X 240 @ 15fps
DVI-RTL Intel VQ PC No 640 X 480 @ 30fps
Indeo Intel VQ Mac, PC Yes 320 X 240 @ 15fps
Motion -JPEG n/a DCT Mac, PC No 640 X 480 @ 60fps
MotiVE Media Vision VQ PC Yes 160 X 120 @ 12fps
MPEG I n/a DCT PC No 320 X 240 @ 30fps
MPEG II n/a DCT PC No 704 X 480 @ 60fps
Px64 n/a DCT Mac, PC No 352 X 288 @ 15fps
Pro-Frac TMM RLE PC Yes 320 X 200 @ 30fps
SoftVideo TMM RLE PC Yes 640 X 480 @ 15fps
Ultimotion IBM n/a OS/2 Yes 320 X 240 @ 30fps
Video Apple VQ Mac Yes 160 X 120 @ 15fps
Video Cube IMIX/Aware Wavelet Proprietary No 640 X 480 @ 60fps
MPEGMPEG was designed for digital video. MPEG uses the same algorithms as JPEG to create one I-frame, then removes the redundancy from successive frames by predicting them from the I-frame and encoding only the difference from its predictions. This is called interframe compression. The MPEG committee created two standards, MPEG I that can play back from a single speed CD-ROM (150 KB per second) at 320 X 240 at 30 fps and MPEG II with enough data (1.2 MB/second) to encode studio-quality video at 704 X 480 at 30 frames per second.
Cinepak - SuperMac TechnologyCinepak is a vector quantization based codec developed specifically to deliver 24-bit video in quarter screen (320 X 240 pixel) windows from files restricted to single-spin CD-ROM data rates. Vector quantization stores information about differences between frames of video by quantifying the magnitude and direction of a pixel's movement. Cinepak's decompressor then uses a CLUT (color lookup table) to recreate the color of each pixel in a frame.
Cinepak is a highly asymmetric codec, with a compression process that takes 300 times longer than decompression. However, Cinepak has a highly efficient decompression and playback scheme and is integrated into Apple's Quicktime 1.5. SuperMac has expanded Cinepak to other major platforms by licensing the codec for use in such products as Microsoft's Video for Windows 1.1, Creative Lab's VideoSpigot for the PC and Sega's Genesis CD-based systems.
The general opinion is that Cinepak is better than Indeo for action sequences and is typically faster at 16 and 24-bit playback. Cinepak's quality compared to Indeo slips for "talking head" and other low-motion sequences.
Indeo - IntelIntel's Indeo, a subset of that company's DVI software. Indeo (currently upgrading from Indeo R2 to R3) defines the format for video capture used by Intel's Intelligent Smart Video Recorder (ISVR) hardware, which permits it to compress in real time. It is currently one of the more highly-regarded video codecs for desktop computer applications. Indeo produces the highest-quality "talking-head" sequences at very low data rates but it is worse than Cinepak for action sequences. It is slightly faster than Cinepak at compression but is still slow.
Indeo is a proprietary blend of color sampling, vector quantization, and run-length encoding. Indeo, which is the past, depended on the use of an i750 chip set for decompression, now plays back on 486 platforms without any additional hardware. One of Indeo's valuable characteristics is its scalability. Indeo will deliver a movie clip a higher frame rates when more processing power is available.
Indeo has a strong following on multiple platforms through licensing with Apple, IBM and Microsoft. In addition, more than 20 independent software vendors support Indeo video in applications such as editors, presentation programs, morphing software, screen savers and utilities.
Video1 and MotiVE - Media VisionMotiVE is a discrete cosine based codec which was licensed by Microsoft as the cornerstone of Microsoft Video 1 which was the primary codec in Video for Windows 1.0.
RLE - MicrosoftThis codec was released with Video for Windows 1.0. It is a simple codec which is optimized for animations or cartoons, but gives relatively poor performance for real-life images.
DVI - IntelIntel's Digital Video Interactive (DVI) standard uses interframe video compression techniques similar to that of MPEG and ADPCM audio compression compatible with CDROM XA standards. DVI provides different levels of quality for video and audio data. For high resolution, full-color digital video with stereo quality approaching that of audio CDs, compression becomes so time-consuming, that special supercomputers must handle the conversion. A compression service bureau can be used to perform DVI compression.