Codec coming to a mux near you
SILICON VALLEY, CALIF.
H.264 is a new video coding standard that promises to reduce the bandwidth necessary for HDTV transmission and distribution. It promises to be twice as efficient as existing video codecs and is in the process of being incorporated into the MPEG -- 4 standard as MPEG -- 4 Part 10.
H.264 codecs can be used over the full range of video coding available under MPEG -- 4 from coding video transmitted over cellular networks to the transmission of high -- quality high-definition video.
The standard, on the verge of ratifications, is a collaborative effort of a Joint Video Team formed by the ITU (International Telecommunication Union) and ISO/IEC. It seems inevitable that companies offering MPEG-4 coding products will eventually adopt H.264 as the video codec of choice.
HD PLANS
Modulus Video, a Silicon Valley startup, is planning to offer H.264 encoders for HDTV.
"Our focus is on implementing H.264 in order to create the highest quality video," explained Rob Robinett, Modulus Video CEO. "Our initial focus will be on the coding of high-definition television signals."
Using H.264 coding, Modulus believes it can code HD quality video at bit rates between 4 and 6 Mbps.
At the NAB2003, Modulus demonstrated a prototype real-time HD encoder at 6 Mbps using a rack of Intel processors. This impressive demonstration showed HD encoding is possible at relatively low bit -- rates using ubiquitous off -- the-shelf microprocessors.
Envivio, a company that provides MPEG-4 solutions, expects to embrace H.264 in the future.
"H.264 has a lot of customer interest," said Envivio spokeswoman Susan Steerman. "It will become prevalent over time."
While Envivio has not yet determined the appropriate bit -- rate for high -- definition video, 5 Mpbs HD video encoded using an H.264 codec should be within reach, said Steerman. "The quality is pretty incredible for such efficient coding."
Robinett said that with H.264, there is no one single feature that improves compression efficiency. "It's a series of incremental improvements that results in more than double the compression efficiency," he said.
Robinett explained that with MPEG-2 there is one block size of 16x16 pixels. H.264 uses similar techniques to achieve video compression, but it has seven differently shaped blocks at its disposal including blocks of 8x16, 16x8 and 8x4 pixels and other sizes.
"The result is that the compressor can choose to more efficiently describe an image," said Robinett.
Another example of how H.264 achieves both superior quality and efficiency is its use of five reference frames for motion estimation and compensation. By comparison, MPEG-2 uses two reference frames.
H.264 also offers superior run length compression schemes as it supports two types of entropy coding: Variable Length Coding (VLC) and Context Adaptive Binary Arithmetic Coding (CABAC). CABAC offers a far more efficient form of run-length coding by exploiting correlations between symbols.
"By adding complexity we can improve efficiency," said Robinett.
H.264 may find its first market in the DVD arena. The current generation of DVD players uses inexpensive red lasers. Using MPEG-2, it is only possible to record somewhere between 20 to 45 minutes of HD on a DVD. But with the H.264 codec, it will be possible to record full -- length movies with high -- definition quality on a red-laser DVD.
The other choice for the DVD manufacturers is moving to blue-laser technology, which increases by four to six times the bit capacity of a DVD. The downside is that blue -- laser technology will be more expensive than red -- laser technology, as red -- laser DVD players have been mass -- produced for years.
"The promise of H.264 in the DVD market is that you can use the same DVD player that already exists," Robinett said. "All you need to do is enhance one chip, the video decoder chip. There are 4 million HD-ready sets out there today. It's a potentially big market and it's a ready market for HD-DVD."
MOORE'S LAW
Robinett says there have been huge advances in technology in the 10 years between the adoption of MPEG-2 and H.264.
"The original MPEG-2 decoder design skimped on the use of memory due to fears about the cost of memory," he said. "Today, memory chips in MPEG-2 decoders are four to eight times bigger than necessary because it is not possible to source smaller amounts of memory. MPEG-2 is archaic really.
"Moore's law has been at work for MPEG encoding. Modulus is trying to exploit all that RAM and computational power," he said.
The giant in the MPEG-4 streaming media world is Microsoft. While Windows Media Player 9 is targeted at streaming video over IP networks and not the world of broadcast television it too will undoubtedly need to deal with the impact of H.264 on its proprietary technology.
Modulus Video, a company composed of veterans of Divicom and Harmonic Inc., plans to offer real-time HD encoders for broadcast use. It expects to begin beta testing an H.264 hardware codec in late 2003.
"It will be possible to plug these encoders directly into an MPEG mux," said Robinett. "The Modulus HD encoder will be compatible with legacy MPEG-2 products."
Envivio's Steerman said that his company is pursuing HD using the MPEG-4 Advanced Simple Profile, now in beta testing. "Once H.264 is standardized we plan to offer HD solutions using an H.264 codec," he said.
At press time, H.264 standardization in both the MPEG committee and the ITU was imminent. Just as DTV allowed broadcasters to deliver HDTV in a 6 MHz channel, it may be H.264 that allows broadcasters, telephone companies and cable systems to finally deliver on the HD promise.
