The Other Side of Compression

Chapter 6: Media Metasis’ ZygoVideo

ZygoVideo, Media Metastasis

PROS	CONS
Real-time software compression at low bit rates.	Keyframes are large, so true streaming would be difficult.
Good date rate tracking at modem rates, always hitting just below the target bit rate requested.	Large differential in quality between keyframes and difference frames causes some strobing effects as the display hits the higher-quality keyframes.
Handles frame sizes up to 240x180 at modem bit rates.	Data rate tracking is not as developed for broadband rates. Results were often well below the requested target bit rates.
Good support pages and templates for getting started.	No pre- or post-processing built in for improving quality.

Media Metastasis’ ZygoVideo ($79) is a compelling addition to the codec selections in QuickTime, with a component download available for QT 5.0 today. According to company sources, Media Metastasis wants to be competitive with Real and Microsoft, but up until now has focused development on the low-end modem market. At lower bit rates, ZygoVideo offers good quality and a fast encoding turn-around. Small video producers looking to put content on their Web sites for progressive download to modem clients will find compelling reasons to look at ZygoVideo.

Encoding using ZygoVideo Pro is accomplished in QT Pro, available at www.apple.com, or in Cleaner 5. It also comes with a basic guide to using the codec, which makes recommendations for frame sizes and frame rates for various target bit rates. Zygo works well with higher pixel counts, so it is possible to achieve larger frame sizes even at modem rates. The documentation recommends 240x180, although we used 160x120 in our testing in order to keep an even playing field for this review, and achieved very good results at 30Kbps.

Other codecs allow frames to drop during the encoding process if they can’t maintain the target bit rate. The result, of course, is jerky playback for the end-user, as the frames being decoded and displayed are not separated by constant time intervals. In other words, codecs that drop frames randomly might end up with a sequence like this: XXX_X_X_XX_XXX_X_XX, where the X’s represent the original frames that are actually encoded. ZygoVideo doesn’t drop frames during the encode, but needs frame rates that are one-half or one-quarter of the original, resulting in this sequence: X_X_X_X_X_X_X_X_X_X. In this manner, smooth motion playback is achieved while maintaining good image quality.

One caveat to using this codec is that the keyframes, which apply a wavelet compression algorithm, are very bit rate intensive. As a result, progressive download is the recommended delivery mechanism. As with most other modern codecs, difference frames are based on the DCT, but as wavelet compression techniques evolve, this may be one to watch.

Overall, the quality of the encodes using ZygoVideo was very good; the codec met its target bit rate or fell just under in almost all cases. On our test platform, real-time encoding performance was achieved for low bit rates and developments are in the works to extend that to broadband encoding. QuickTime could use a new real-time codec in the mix, and while we wouldn’t use ZygoVideo over Sorenson 3, we would say that we see lots of room for improvement in the ZygoVideo codec, especially for real-time webcasting applications.

Tips and Tricks for Encoding with ZygoVideo:

1. Keep the frame rate to one-half or one-quarter the source rate.
2. Add the "smoothing to low bit rate encodes" for improved image quality.
3. Let the codec do all key frame control. Unselect the "Keyframe Every" box, or enter a very large number so the application doesn’t put in key frames where they are not needed.

Wrapping Up

All of the codecs we reviewed are suitable for video on demand applications. ZygoVideo targets QuickTime clients on modem connections with higher frame sizes than we are used to seeing today. If you are looking at cross-platform support and very high quality at broadband rates, VP3 is a viable option. Hopefully we will start to see features and flexibility added by the open source community.

Broadcast and DVD quality VOD content providers should look at DivX and VP4 as highly competitive with Real and Windows Media codecs today.

At the very least, alternative codecs keep the heat on the proprietary technology we have been living with for several years. But with solid, full-screen, full-motion potential, real-time encoding capabilities and open source availability, these codecs all offer something to the streaming media community beyond the de-facto standards of today.