28 Mar

HEVC/H.265: Everything you need to know

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HEVC - H.265 HEVC - H.265 RedShark


Cunning H.265

The successor to h.264 is, cunningly, h.265, an ITU standard just a fraction away from being approved at the time of writing that's based on the High Efficiency Video Coding (HEVC) system. As we’ve seen, the complexity and therefore effectiveness of video codecs is largely controlled by the performance of the devices on which they will be replayed. HEVC leverages improvements in the performance of consumer electronics, aiming to achieve the same image quality at half the bitrate of h.264 through the application of more advanced image-encoding techniques, while being no more than three times harder to decode than High-profile h.264. On the face of it, this seems like a questionable deal, with a tripling of requirements while only doubling performance, but with Arm and Intel currently competing quite effectively to create electronics that do more work for less money and less electricity, this seems like a rather ungenerous criticism.

Achievements in improving the performance of compression codecs have been mainly regulated by the performance of the consumer devices that must decode and display content, and recent improvements in this area have made ever more complex and effective codecs feasible. HEVC is recognisably a development of h.264, and as the overview to the specification states, there is no one major change that accounts much more than any other for the improvement in performance.

Variable block size

This is inevitably a very partial and incomplete discussion as the complete HEVC specification is neither short nor simple, but perhaps most fundamentally, HEVC does not start by breaking the image up into squares of equal size, as had been the case in previous standards. Instead, it has the flexibility to select the block size to maximise the effectiveness of its other techniques, depending on the image content. The block size itself is, optionally, larger – up to 64 pixels square, as opposed to 16 – which makes for additional efficiencies, especially on the more CPU-intensive profiles of HEVC which require the use of larger blocks. Beyond this, HEVC has the option  to break these larger blocks down into smaller ones, treating the smaller blocks individually with regard to the encoding techniques that are used to compress them.





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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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