The unrelenting advance of video compression
Leonardo Chiariglione, Digital Media Strategist,
Convenor of ISO / IEC JTC 1 / SC 29 / WG 11, the Moving Pictures Experts Group (MPEG) working group
Ever since people first realized that digital technologies could be used to store and transmit video signals with greater fidelity, the problem of the amount of bits required to do so became apparent. The analogue television signals still in common use today have a bandwidth of about 5 MHz. Converted into bits, this generates 216 Mbit/s (million bits per second) some 20 times more than the bitrate of a good ADSL modem !
Ask smart people to solve a well-formulated problem and you are bound to get a solution. This was the case of video compression. The problem was to reduce the number of bits/s required to store or transmit video signals. The smart people were the thousands of researchers who invested time and effort to reduce the bitrate of digital video to low levels. It did not happen overnight. The first applications were driven by the idea that people would like to communicate with video in addition to audio. In the early 1990s the first standard produced by the Moving Picture Experts Group or MPEG (Working Group 11 of ISO/IEC JTC 1/SC 29) targeted storage of digital video on compact disc (CD). MPEG-1, as the standard is called, is used in hundreds of millions of Video CD players. In the mid-1990s, MPEG developed MPEG-2 that is being used in hundreds of millions of digital television set top boxes and Digital Versatile Disc (DVD) players.
In the late 1990s, MPEG developed MPEG-4 that is widely used to move digital video files on the web, to view video on cell phones or to store digital video in a computer-friendly fashion.
All these standards were characterized by advances in the technologies used to compress video signals. In 2000, MPEG started inquiring if new technologies had been developed that would further compress video. In 2001, a Call for Evidence was issued asking the industry to bring evidence that video could be further compressed compared to MPEG-4. The evidence confirmed the validity of the request, and the decision to develop a new part (part 10) of the MPEG-4 standard called Advanced Video Coding (AVC) was taken, this time in collaboration with ITU-T (as had been the case for MPEG-2). ISO/IEC 14496-15:2004, Information technology Coding of audio-visual objects Part 15 : Advanced Video Coding (AVC), was approved as FDIS in July 2003.
AVC video compression of the new generation
There is an understandable tendency on the part of salesmen to overstate the quality of their wares ; MPEG could similarly boast the wonders of its new product . This is not, however, what MPEG does for the audio and video compression standards it develops. When a compression standard nears completion, verification tests are run, using sophisticated techniques that transform the results of a large number of subjective evaluations into objective measures. For AVC it was found that on average the compression performance of AVC is twice that of MPEG-2 and MPEG-4 part 2 (the original MPEG-4 standard).
This is an impressive result and there is a lot of excitement in the industry at the possibilities opened up by this new standard. AVC can be used in at least two new ways : to replace older standards for the same type of application or to use the new standard for new applications. One of the possibilities of the former is to use AVC as the video compression of the new generation DVD that is being discussed in the appropriate fora. Another is to use AVC to provide improved picture quality on such constrained-bandwidth applications as video on mobile devices.
When a new technology replaces an old one in widely deployed applications and devices there is always some resistance because of the need to cater for the transition between the old and the new. This is not, however, the case for new applications, such as digital video on the Internet, for which there have been little more than trials.
AVC can be the video compression technology of choice along with another successful MPEG technology for audio compression, Advanced Audio Coding (AAC) for what is likely to become the marriage between networks and media.
Is this the end of the story for video compression ? Most likely not. In December 2003, MPEG issued a Call for Proposals for video compression technologies with scalable features, and in March 2004 received a large number of responses. MPEG is now busy working on a new video compression standard that is expected to see the light toward the end of 2006.
Get ready for more compression with more features !
About the author
Dr. Leonardo Chiariglione is Convenor of the Moving Pictures Experts Group (MPEG), the working group which produced the MPEG-1, MPEG-2 and MPEG-4 standards that support rich-media applications on diverse delivery systems, MPEG-7, that supports advanced search and retrieval of audio-visual content and is developing MPEG-21, the Multimedia Framework and MPEG-A, the Multimedia Application Formats.