Compression and interconnect breakthroughs pave a path for advanced multimedia formats
By Brian Dipert -- EDN, January 24, 2002
Microsoft adds to the already-impressive audio and video capabilities of its Windows Media Technologies codecs in the upcoming Corona technology, which is now in beta testing and which the company previewed at the Streaming Media East show, which took place on Dec 10 to 13, 2001, in New York. Microsoft claims that its next-generation WMV (Windows Media Video) can deliver a 24-frame/sec, 720-line progressive-scan video stream in, on average, half the bit rate that 480-line interlaced MPEG-2 on DVD-Video discs uses. The DVD Forum (www.dvdforum.com) is reportedly evaluating Corona, presumably in conjunction with Microsoft's media-identification and -security technology, along with MPEG-4, for possible use in next-generation high-resolution DVD-Video, as it strives to avoid an expensive infrastructure migration to blue-light lasers.
The next iteration of one- and two-channel WMA (Windows Media Audio), now called WMA Consumer, will deliver 20% better quality at a given bit rate than today's WMA8; in other words, it provides equivalent quality to WMA8 at a 20% lower bit rate. Like WMA8, WMA Consumer will be compatible with WMA7 decoders installed on many PCs and now built into many consumer-electronics devices. WMA Professional, on the other hand, will not be backward-compatible with earlier WMA decoders. In exchange, though, it offers as many as six channels of 24-bit, 96-kHz audio, specifications that exceed those of today's Dolby Digital codec on DVD-Video discs and that match the six-channel sample rate and size of DVD-Audio—albeit not with DVD-Audio's lossless compression—and 24-bit, 96-kHz DTS. Bit rates for WMA Professional at a 16-bit sample size and 48-kHz sampling rate are as low as 128 kbps (no typo, that's only a little more than 20 kbps per channel for each of the six full-frequency range channels), and 24-bit, 48-kHz source material can compress to bit rates as low as 192 kbps.
At Streaming Media East, several DVD-decoder-chip suppliers announced plans to build Windows Media support into their products. And it's increasingly likely that the high-resolution audio interconnect between those DVD players and their corresponding home-theater receivers may migrate from today's six analog channels to a lossless digital link, IEEE-1394 (see "'Bassless' buzz impairs advanced audio's image," EDN, May 24, 2001, pg 20). The DVD Forum's Guideline of Transmission and Control for DVD-Video/Audio through IEEE1394 Bus still requires that the DVD player handle any required audio decompression to linear PCM (pulse-code modulation), and it sidesteps the all-important issue of media security, necessary to bring Hollywood onboard (see "Media security thwarts temptation, permits prosecution," EDN, June 22, 2000, pg 101). But digital interconnect will route the audio through presumably higher quality DACs inside the receiver, reducing DVD-player prices in the process. Digital interconnect will also re-enable bass management, a feature that today's DVD-Audio and SACD players implement either clumsily or not at all, and other digital-domain audio-processing functions. Access the DVD Forum's guidelines at www.dvdforum.com/tech-guideline.htm.
Microsoft, 1-425-882-8080, www.microsoft.com/windows/windowsmedia.
