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28 Mar

HEVC/H.265: Everything you need to know

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HEVC - H.265 HEVC - H.265 RedShark


In a major new article, Phil Rhodes explores the background to HEVC/H.265, and explains what makes it so good at compressing video. Read this if you want to know how almost all video - including 4K - will be delivered in the near future

Since almost the first days of digital video, there’s been a need to reduce the otherwise unmanageable amount of data that uncompressed video represents. While it’s now relatively straightforward to handle standard-definition, and even high definition, video as a sequence of unadulterated bitmaps, the demand for ever-higher resolution means that efficiently reducing the bitrate of video is going to be an issue for as long as people need to sell televisions.

Compression has been around since the early 90s

Video compression became a mass-market technology in the early 90s, with the release of Quicktime in December 1991 and Video for Windows a year or so later. At the time, the performance of video codecs – in terms of the ratio of bitrate to image quality – was limited mainly by the performance of the system that decoded it, which invariably meant the CPU of a desktop PC. Video codecs are generally highly asymmetric, with encoding taking more work than decoding, often multiples of realtime to encode – but they must usually be decoded in realtime. At the time, Intel’s 486 processor line was ascendant, but with performance limited to perhaps fifty million instructions per second, use of an  encoding scheme such as the now-current h.264/MPEG-4 AVC was impractical. Both Video for Windows and Quicktime were initially most often used with Cinepak, a codec  based on wildly different techniques to more modern ones, but with the key feature that it was designed to work in what, by modern standards, seem extremely modest circumstances. Decoding 320 by 240 frames, at the 150 kilobytes per second of a single-speed CD-ROM drive, is something you can absolutely do with h.264 – but you couldn’t have decoded it on the CPU of a Sega Mega Drive (er, Genesis, Americans) games console, circa 1990.

Drive for better quality

The drive for better quality for the bitrate, as well as the need for better absolute quality and higher resolution, is nothing new, and has largely advanced in step with the ability of ever-improving hardware to handle more elaborate codec techniques. Through the late 90s, approaches that are recognisably the technological forerunner of current codecs began to emerge, particularly h.261 in 1998 which was designed to stream video over ISDN lines from 64Kbps upward. Through the last decade or so, and ever-increasing H-numbers (which come from ITU-T Recommendation numbers), the performance of video codecs has improved more or less alongside the ability of affordable electronics to decode them. This is good, given the explosive success of video-on-demand services and the resulting pressures placed on internet and cellular network bandwidth. One would be forgiven for assuming, with maximum cynicism and misanthropy, that the work involved in all this improvement is being done mainly so that people can send us lots more advertising without having to upgrade their technology. Either way, it’s now clear that the internet and various riffs on video over IP technology is what’s going to provide the video-on-demand experience that’s been discussed since the 80s, even if the people who developed the protocols on which the internet runs probably didn’t foresee this use.

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  • I have a question that wasn't covered in this article.

    Do HEVC hardware decoders aim to achieve 4k 3D at 48fps or is it still aiming for a 23fps standard? If so, then I welcome the HEVC 4k 48fps 3D overlords.

    I don't care what anybody says. I like the increasing standards of quality for movies. I have always been a huge fan of 1080p and Blu-ray, and I really look forward to the next quality leap. I do like 3D, but I feel like 3D is being hindered by displays and Blu-ray players. The picture is a bit pixilated compared to non 3D footage.. which is something I expect will improve with 4k players.

    If there's one thing that disappoints me about current gen H.264 hardware decoders, it's that they are only capable of handling 1080p at 30fps max. I know of no h.264 hardware solution that can handle 48 or 60fps... Only a powerful PC can handle this.

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  • I personally haven't noticed pixelation with 3D Bluray content on my 3D set but passive 3D displays use a polarized filter that halves the screen resolution, which may be where you are seeing pixelation.

    As far H.264 decoders not handling 48fps or 60fps content, this is not quite true. Frame rate and frame size are fairly arbitrary and I have authored content at 60fps 1080p that played fine on many Bluray players including Playstation3 and on every LCD/LED I tried. The PS3's Bluray drive seemed to stutter at just around 6MB/sec but I was able to push near lossless-quality 1080p/60fps at it with some tweaking of x264 encode parameters.

    I frankly love the vividness of 48fps and 60fps and hope more films are shot and released in it.

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  • I was hoping to see a comparison between HEVC and VP8. Hopefully you may be able to cover the differences in a later article.

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  • As far as I can see, the purpose of VP8 is not particularly to compete with H.264 (let alone HEVC/H.265) on a technological level - it's more about producing a patent-free alternative. So, I don't think it's actually a very interesting comparison. Most tests to date suggest that H.264 has a trivial performance advantage over VP8, so it isn't going to compete with HEVC. And as I say, I don't think that's really the point anyway.

    The relevance of VP8 is also reliant on them actually getting anyone to use it.

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  • I'd love to hear some other editors weigh in on HEVC.
    Which NLE's are already offering the codec in their updates?
    If anyone has had a chance to try it, what does it feel like scrubbing on your favorite NLE timeline, what's it like to encode, and does it bring back the sleepless nights where you're wondering if your workstation crashed midway through the render?

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  • Actually, Jeffery, I don't think it's being used in any NLEs at the moment. It will almost certainly harder to edit with natively than H.264 - which is already hard enough! You would hope that it might only be used as a "delivery" format rather than a production and acquisition one - but that's what we thought about H.264 until AVCHD came along!

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  • Nice article, thanks. Just a comment on availability - the standard is now finalised but availability of tools, even for experimentation, is still limited. If you want to try HEVC playback for yourself, you might find this guide useful:
    - I've explained how to download an HEVC player and I've uploaded some test clips encoded with HEVC and H.264.

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Phil Rhodes

Phil Rhodes is a Cinematographer, Technologist, Writer and above all Communicator. Never afraid to speak his mind, and always worth listening to, he's a frequent contributor to RedShark.

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