5 Sep 2014

4K or Ultra High Definition (UHD) video has four times the detail of 1080p full HD. How do you deliver such high resolution video to a TV or mobile device over a limited bandwidth connection? Next-generation video codecs may provide the answer. This article, part 3 of “How to stream better quality video”, gives an overview of two new video codecs: High Efficiency Video Coding (HEVC or H.265) and VP9.

The High Efficiency Video Coding standard

H.264 is widely used amongst broadcasters and in the online video streaming industry, but this may change with the introduction of HEVC. If you want to get up to speed on the technical side of HEVC, the Vcodex website has material to get you started.

Key features of HEVC:
  • Up to twice as efficient as H.264 - which means that you can send the same picture quality using much smaller files.
  • Support for resolution up to 8K video (7680 × 4320) and frame rates up to 120 frames per second.
  • Improved picture quality in terms of noise levels, color spaces and dynamic range.
This means you can shoot and produce video at the higher resolutions of UHD/4K without dramatically increasing the bandwidth required to broadcast or stream your video.
VP9 is Google’s answer to the problem of streaming 4K video. Offered as royalty free by Google, VP9 also claims to be significantly more efficient than H.264. Like HEVC, VP9 supports compression of videos at resolutions above HD as part of the WebM media format.

When can I start using 4K / Ultra High Definition?
You can try 4K on the web right now. For example, this Youtube playlist features 4K/UHD videos, which your display may or may not be able to handle. DivX's HEVC showcase includes examples of 4K videos. You'll need to download the DivX HEVC plugin to play back these clips.

Hardware support for HEVC is increasing, with a number of demonstrations at this year's IBC show. A reference hardware implementation of VP9 is available for chip developers.

New codecs - a performance comparison
We ran a comparison test to find out how HEVC and VP9 codecs performed compared with H.264 using a 720p video clip downloaded from the Xiph website. Following standard test guidelines for video quality assessment, we carried out subjective video quality tests with 10 non-expert users.
Figure 1: File size versus perceptual quality for H.264, VP9 and HEVC codecs

Figure 1 shows the variation of perceptual video quality measured as mean opinion score (MOS), with file size for different codecs. At the higher end of the quality scale (i.e. lower compression), both HEVC and VP9 achieve a similar viewing quality to H.264 with a 40-45% reduction in file size. At lower quality ratings, the gains of HEVC and VP9 are smaller.

This implies that you should see the most benefit from HEVC and VP9 codecs at high quality / low compression settings.

We hope the three-part series of the blog "How to stream better quality video" has been useful.

About the authors:

Iain Richardson is an internationally known expert on video compression and the author of several books, including The H.264 Advanced Video Compression Standard

Abharana Bhat specialises in video compression, media streaming and video quality assessment.

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