Broadcast & Distribution – HEVC, or “High Efficiency Video Coding,” is showing promise to make internet-delivered Ultra-HDTV a reality, as it can provide about a 50% bitrate saving over MPEG 4/AVC (H.264), becoming a practical solution to offering 4k content to the home.
But while MPEG and HEVC have been developed by standards committees fronting for a panoply of industrial players, Google has independently been developing an alternative, called VP9.
Many of the tools used in VP9 (and its predecessor, VP8, originally developed by On2 Technologies) are actually similar to those used in HEVC: transforms, blocks, quantization, motion estimation, etc. And VP9 supports the image format needed for internet video: 4:2:0 color sampling, 8 bits-per-channel color depth, progressive scan and image dimensions up to 16,383 x 16,383 pixels; it can also support 4:4:4 chroma and up to 12 bits per sample. The Chromium, Chrome, Firefox and Opera browsers now support playing VP9 video in the HTML5 video tag; both VP8 and VP9 video are usually encapsulated in a format called WebM, a Matroska-based container also supported by Google, which can carry Vorbis or Opus audio.
From a performance standpoint, Google says that VP9 offers a 50% compression gain over H.264 standards – essentially saying that it performs on par with HEVC. Some video experts disagree with this claim, but since video quality is ultimately an objective measure, performance depends on test materials, codec settings and viewers, all of which will produce statistical variation.
With YouTube owned and operated by Google, market considerations have motivated the company to develop VP9 as a royalty-free alternative to HEVC, and so the codec’s algorithms have been cleverly constrained or modified, in order to avoid the intellectual property used in the MPEG standards. Last year, Google and MPEG LA LLC – the private firm that oversees “essential patents” owned by numerous companies participating in the MPEG patent pool – announced that they entered into agreements granting Google a license to techniques that may be essential to VP8 and earlier-generation VPx video compression technologies under patents owned by 11 patent holders. While there is no license fee required to use VP8, there are other terms imposed – a so-called FRAND-zero license – so users may still need a license to fully benefit from the Google-MPEG-LA agreement. No word yet on what this all means concerning VP9.
Despite its capital strength, Google may still have an uphill battle with VP9, as HEVC has already gained a small but growing following in both encoding and decoding applications, including several U-HDTV displays and internet-video boxes. Not one to let progress stand still, however, Google has announced that development on VP10 has begun and revisions are likely to follow. Aldo Cugnini