We visited Broadcom to meet with Sandy MacInnis, Technical Director, Digital Video Technology. In a telephone conversation several months ago, Sandy filled us in on why a new video compression standard is needed and what the standard promises. He said it was hard to describe the differences over the phone and invited us to see some demonstrations. Although the bulk of our conversation was technical, it was refreshing that Sandy's bottom line about his work is "what matters in the end is what real viewers perceive".
MPEG-2 is the most widely-used standard for broadcast-quality digital video - it is used by nearly all digital video broadcasting over satellite and cable, on DVDs, and for high-definition (HD) TV. The video compression/decompression algorithm or "codec" is a major component of MPEG-2. By today's standards, this video codec is fairly inefficient, requiring 3 to 6 Mbps for standard-definition (SD) TV and about 20 Mbps for HD. The development work was done in the 1980s and the standard was approved nearly a decade ago; advances in compression algorithms and semiconductors have produced more efficient compression algorithms requiring more processing power.
AVC versus MPEG-4
What will probably become the standard for the next decade or so goes under many different names: AVC, H.26L, H.264, JVT, Part 10. This comes from the many organizations working on the specifications: ISO/IEC calls it MPEG-4 AVC (for "advanced video coding" and shortened to AVC), while ITU-T calls it H.264 (formerly H.24L). It is also referred to as "JVT" for the "joint video team" that developed it. These global standards bodies are working together to define the new standard, which will formally become ITU-T H.264 and ISO/IEC MPEG-4 Part 10. The technical specifications will be completed soon and the standard is expected to be ratified during 2003. Products will come to market over the next few years.
The MPEG-4 standards were ratified some time ago; like MPEG-2, they cover many things besides video compression. The MPEG-4 video codec improves on MPEG-2 by a factor of two, and many people had thought that it would replace MPEG-2 in new products. But the consensus now seems to be that AVC -- with an additional 1.5X improvement -- will be used instead.
Sports scenes are difficult to compress well, and are often used to compare video codecs. Sandy said that AVC produces very good results at 1 Mbps for SD and at less than 6 Mbps for HD - improvements of 3X over MPEG-2. We spent a while with him looking at football videos (American football, that is) and found it very hard to see much difference between the various codecs. Only by looking very carefully could we see differences in the texture of the grass or the detail of a player's hair in a closeup.
Next-Generation Digital Set-Top Boxes
The critical question is which video codec will be built into tomorrow's digital set-top boxes. These boxes are used to receive subscription video programming, whether tranmitted over cable or over a satellite. Unlike PCs, digital set-tops are usually fixed in their functions: while video codecs like MPEG-2 and RealVideo can be downloaded to operate as part of the software in today's PCs, codecs are "hard wired" in a digital set-top. Millions of digital set-tops are in use all over the world -- and virtually every one built to date is based on MPEG-2.
HD is driving subscription video service providers to a decision on new codecs. With the transition under way to HD, with each HD channel occupying four to six times the bandwidth of an SD channel, and with a fixed amount of satellite and cable bandwidth, service providers must decide whether to sharply reduce the number of channels or to face the difficult decision of defining a new generation of set-tops.
While HD digital set-tops based on MPEG-2 have been available for a year or so, the total installed base is still very small. With the AVC/JVT/H.264/MPEG-4 Part 10 standard headed for ratification, we expect service providers will soon choose it as a key component of the digital set-tops to be deployed over the next decade.
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