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Beyond MPEG-2

Oct 1, 2006 12:00 PM, BY CRAIG BIRKMAIER

No one said transitioning to H.264 would be simple.

Hans Hoffman, EBU and past SMPTE engineering director for television, points to the picture-quality differences when over-sampled HDTV source is encoded as 720p/50, 1080i/50 and 1080p/50 for emission using H.264 compression, during an EBU format demo at IBC.

For the past few years, analysts who watch the rapidly expanding universe of video distribution options have been waiting for Apple CEO Steve Jobs to take the next big step — to bring about the long anticipated convergence of video and computing. Last year, they were tantalized when Jobs announced the video iPod and the availability of several hit ABC television shows through the iTunes Store. When Jobs successfully negotiated the merger of Disney and Pixar, taking a seat on Disney's board of directors, some analysts expected that he would soon announce a movie download service and a consumer-electronics-oriented product for the big-screen TV in the family room.

The wait is almost over. In September, Apple announced a movie download service, bringing titles from Disney movie studios to the PC and the small screen of a video iPod. During the announcement, Jobs noted that in less than a year, offerings grew from five shows to 220 shows, drawing from more than 40 networks. Customers have downloaded more than 45 million TV shows.

Then in an uncharacteristic move, Apple's CEO pre-announced a new product that will be introduced early next year. Code named iTV, this diminutive box will bring TV shows, movies, podcasts, and the music and digital photo collections to a user's big-screen TV via analog component or HDMI connections. iTV will use WiFi wireless or a wired Ethernet connection to link to the Mac or PC.

All of this raises an important question: Will the quality of the content stand up to the demands of a big-screen TV, which is increasingly being filled with HD imagery? Apple claimed to be increasing the encoding parameters for all of the video that will be downloaded from the iTunes Store from 320 × 240 to 640 × 480, calling it “near DVD quality.” But even at this resolution, it will take 30 minutes to download a movie via a 3Mb/s broadband connection. Users may need to wait for even faster broadband connections to download 720p HDTV.

The H.264 (MPEG-4 AVC) encoding technology being used by Apple is proving that it is up to the task over a wide range of resolutions for mobile video, SD and HD television, and digital cinema applications. H.264 is one of three approved encoding technologies for the next generation of high-definition DVD formats — HD-DVD and Blu-ray. These new DVD formats will also support MPEG-2 and the Windows Media codec developed by Microsoft (recently standardized as SMPTE VC-1).

Not to be outdone, Microsoft has announced Zune, an iPod/iTunes competitor, which will also handle video and will likely use the Windows Media audio and video codecs. Meanwhile, U.S. television broadcasters sit on the sidelines, trying to figure out how they can put these next-generation video encoding technologies to work in a digital broadcast world still locked into legacy MPEG-2 video compression technology. For now, the hotbed of activity for H.264 and VC-1 is the Internet and mobile video.

The legacy problem

All digital video encoders use software algorithms. These algorithms can be run on virtually any PC platform and can be accelerated using several PCs in parallel. When the application requires that content be delivered in real time, a dedicated hardware encoder may prove a better option than a software encoder.

In a rare pre-announcement of a product, Apple CEO Steve Jobs shows an iTV prototype, which will bring digital media content from a Mac or PC to the bigscreen TV in the family room.

Software encoders can produce higher quality results than real-time hardware encoders, as they can run the algorithmic routines to completion. The drawback of hardware encoders is that they only have one frame period in which to run these routines. This may affect the quality of interframe predictions, resulting in lower compression efficiency.

This issue is amplified by the newer algorithms, which are significantly more complex than MPEG-2, requiring about four times the computational power of MPEG-2. Fortunately, this level of power is now available, and encoder manufacturers have learned the benefits of developing real-time products atop programmable computing hardware, which can be upgraded as their implementations evolve.

As the opportunities for new channels of video distribution proliferate, the demands on video encoders will increase as well. It may be necessary to produce multiple versions of your video content for different distribution networks: low resolution/bit rate for mobile applications; somewhat higher quality (approaching SD/DVD quality) for Internet downloads; and SD and HD versions for broadcast, cable, DBS and IPTV. Manufacturers are responding with platforms that can ingest content at the highest quality level and produce multiple versions for distribution, often in real time.

A crowded field

As a final note, these new encoding technologies took center stage at IBC2006. European broadcasters waited to adopt HDTV. They now benefit from that decision with the opportunity to employ next-generation codecs for HDTV.

The European Broadcast Union provided an informative technology demonstration at IBC, examining the quality of the delivered HD images using H.264 encoding technology. The demonstration included another “next-generation” technology, which is now generically being called 1080p/50 or 1080p/60. The source material for the demonstration was shot on 65mm film at 50fps, digitized at 2160p/50, and then downconverted to 1080p/50, 720p/50 and 1080i/25. Other material was shot in native 1920 × 1080p/50 with a HDC1500 CCD camera and also converted to 1080i/25 and 720p/50. All material was encoded using H.264.

According to David Wood, head of new media in the EBU's technical department, “The initial results suggest that even with next-generation displays (full HD 1920 × 1080 pixel resolution), 720p delivery will give better moving picture quality than 1080i/25,” he said. “We know that 1080p/50 is virtually as efficient a broadcast format as 1080i/25. Using content adaptive compression such as MPEG-4 AVC progressive is as efficient as interlacing or more so.”

Craig Birkmaier is a technology consultant at Pcube Labs, and he hosts and moderates the OpenDTV forum.