As consumers increasingly view live and VOD television on a broader range of IP-connected devices, broadcasters are struggling to deliver these high-bandwidth services. However, a new video compression standard called High Efficiency Video Coding (HEVC) promises to improve upon the current compression standard H.264, also known as MPEG-4 AVC, easing broadcasters’ pain. Using HEVC, broadcasters can reduce the data rate needed for high-quality video coding by approximately 50 percent, enabling them to deploy higher quality OTT video services using the same amount of bandwidth, or half the bandwidth at the same quality. In addition to improving OTT delivery, HEVC also has the potential to support a broad range of current and future applications, including 4K x 2K Ultra HD Television (UHDTV), making it an extremely exciting technology that pushes the consumer experience to the next level. (For more information about 4K UHDTV, read the ITU recommendation on the technology, available online at www.itu.int/net/pressoffice/press_releases/2012/31.aspx.)
Evolution of video compression
An uncompressed HD video signal consumes approximately 1.5Gb/s to 2Gb/s of bandwidth. In the 1980s, when video compression was in its infancy, the goal was to compress this down to 130Mb/s. Today, content providers are able to encode HD video between 5Mb/s to 10Mb/s using H.264/MPEG-4 AVC, depending on the quality target resolution and encoding scheme (CRB or VBR). HEVC is designed to push that envelope even further by reducing the bit rate of MPEG-4 by 50 percent. (See Figure 1.)
But, before discussing the improvements of HEVC, it is important to understand the key technologies that HEVC builds on. MPEG-2, in the broadcast and entertainment TV world, was a huge success. It offered full SD quality at 4Mb/s, but the industry quickly realized that MPEG-2 could also enable HD for bandwidth-sensitive networks. Using MPEG-4 AVC compression, it became affordable to transmit HD to the home. In addition to featuring tools for interlace, MPEG-2 added more adaptive coding functionality such as multiple patterns to scan transform coefficients, linear or nonlinear quantization, and changeable coefficient weighting matrixes.
The H.264/MPEG-4 AVC standard refined motion estimation with quarter-pixel precision. It enabled a 50 percent bit-rate reduction compared with MPEG-2, enabling broadcast SD at very low bit rates and broadcast HD at shockingly low bit rates for the time. H.264/ MPEG-4 AVC also added new tools, including sophisticated intra prediction (whereby a prediction block is formed based on previously encoded and reconstructed blocks within the same frame), a better de-blocking filter, new transforms, improved motion compensation interpolation, multiple motion estimation references, weighted prediction and context-based adaptive binary arithmetic coding (CABAC).