GCN 1.2 - Image & Video Processing

AMD’s final set of architectural improvements for GCN 1.2 are focused on image and video processing blocks contained within the GPU. These blocks, though not directly tied to GPU performance, are important to AMD by enabling new functionality and by offering new ways to offload tasks on to fixed function hardware for power saving purposes.

First and foremost then, with GCN 1.2 comes a new version of AMD’s video decode block, the Unified Video Decoder. It has now been some time since UVD has received a significant upgrade, as outside of the addition of VC-1/WMV9 support it has remained relatively unchanged for a couple of GPU generations.

With this newest generation of UVD, AMD is finally catching up to NVIDIA and Intel in H.264 decode capabilities. New to UVD is full support for 4K H.264 video, up to level 5.2 (4Kp60). AMD had previously intended to support 4K up to level 5.1 (4Kp30) on the previous version of UVD, but that never panned out and AMD ultimately disabled that feature. So as of GCN 1.2 hardware decoding of 4K is finally up and working, meaning AMD GPU equipped systems will no longer have to fall back to relatively expensive software decoding for 4K H.264 video.

On a performance basis this newest iteration of UVD is around 3x faster than the previous version. Using DXVA checker we benchmarked it as playing back a 1080p video at 331fps, or roughly 27x real-time. For 1080p decode it has enough processing power to decode multiple streams and then-some, but this kind of performance is necessary for the much higher requirements of 4K decoding.

Video Decode Performance

Speaking of which, we can confirm that 4K decoding is working like a charm. While Media Player Classic Home Cinema’s built-in decoder doesn’t know what to do for 4K on the new UVD, Windows’ built-in codec has no such trouble. Playing back a 4K video using that decoder hit 152fps, more than enough to play back a 4Kp60 video or two. For the moment this also gives AMD a leg-up over NVIDIA; while Kepler products can handle 4Kp30, their video decoders are too slow to sustain 4Kp60, which is something only Maxwell cards such as 750 Ti can currently do. So at least for the moment with R9 285’s competition being composed of Kepler cards, it’s the only enthusiast tier card capable of sustaining 4Kp60 decoding.

This new version of UVD also expands AMD’s supported codec set by 1 with the addition of hardware MJPEG decoding. AMD has previously implemented JPEG decoding for their APUs, so MJPEG is a natural extension of that. Though MJPEG is a fairly uncommon codec for most workloads these days, so outside of perhaps pro video I’m not sure how often this feature will get utilized.

What you won’t find though – and we’re surprised it’s not here – is support for H.265 decoding in any form. While we’re a bit too early for full fixed function H.265 decoders since the specification was only ratified relatively recently, both Intel and NVIDIA have opted to bridge the gap by implementing a hybrid decode mode that mixes software, GPU shader, and fixed function decoding steps. H.265 is still in its infancy, but given the increasingly long shelf lives of video cards, it’s a reasonable bet that Tonga cards will still be in significant use after H.265 takes off. But to give AMD some benefit of the doubt, since a hybrid mode is partially software anyhow, there’s admittedly nothing stopping them from implementing it in a future driver (NVIDIA having done just this for H.265 on Kepler).

Moving on, along with their video decode capabilities, AMD has also improved on their video encode capabilities for GCN 1.2 with a new version of their Video Codec Engine. AMD’s hardware video encoder has received a speed boost to improve its encoding performance at all levels, and after previously being limited to a maximum resolution of 1080p can now encode at resolutions up to 4K. Meanwhile by AMD’s metrics this new version of VCE should be capable of encoding 1080p up to 12x over real time.

A quick performance check finds that while the current version of Cyberlink’s MediaEspresso software isn’t handling 4K video decoding quite right, encoding from a 1080p source shows that the new VCE is roughly 40% faster than the old VCE in our test.

Video Encode Performance (1080p)

4K video is still rather new, so there’s little to watch and even less of a reason to encode. That of course will change over time, but in the meantime the most promising use of a hardware 4K encoder would be 4K gameplay recording through the AMD Gaming Evolved Client’s DVR function.

GCN 1.2: Geometry Performance & Color Compression Meet The Sapphire R9 285 Dual-X OC 2GB
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  • felaki - Wednesday, September 10, 2014 - link

    The article says that the Sapphire card has "1x DL-DVI-I, 1x DL-DVI-D, 1x HDMI, and 1x DisplayPort". Can you be more precise as to which versions of the spec are supported? Is it HDMI 1.4 or HDMI 2.0? I believe since this refers to MST, it's only HDMI 1.4 and a DisplayPort connection is required in MST mode for 4K@60Hz output?

    Reading the recent GPU articles, I'm very puzzled why HDMI 2.0 adoption is still lacking in GPUs and displays, even though the spec has been out there for about a year now. Is the PC industry reluctant to adopt HDMI 2.0 for some (political(?), business(?)) reason? I have heard only bad things about DisplayPort 1.2 MST to carry a 4K@60Hz signal, and I'm thinking it's a buggy hack for a transitional tech period.

    If the AMD newest next-gen graphics card only supports HDMI 1.4, that is mind-boggling. Please tell me I'm confused and this is a HDMI 2.0-capable release?
    Reply
  • Ryan Smith - Wednesday, September 10, 2014 - link

    DisplayPort 1.2 and HDMI 1.4. Tonga does not add new I/O options. Reply
  • felaki - Wednesday, September 10, 2014 - link

    Thanks for clarifying this! Reply
  • Penti - Wednesday, September 10, 2014 - link

    You can do 4K SST on both Nvidia and AMD-cards as long as they are DisplayPort 1.2 capable. It depends on your screen. There is no HDMI 600MHz on any graphics processor. Neither is their much of support from monitors or TVs as most don't do 600MHz. Reply
  • felaki - Wednesday, September 10, 2014 - link

    Thanks! I was not actually aware that SST existed. I see here http://community.amd.com/community/amd-blogs/amd-g... that AMD is referring to SST as being the thing to fix up the 4K issue, although the people in the comments on that link refer that the setup is not working properly.

    How do people generally see SST? Should one defer buying a new system now until proper HDMI 2.0 support comes along, or is SST+DisplayPort 1.2 already a glitch-free user experience for 4K@60Hz?
    Reply
  • Kjella - Wednesday, September 10, 2014 - link

    Got 3840x2160x60Hz using SST/DP and it's been fine, except UHD gaming is trying to kill my graphics card. Reply
  • mczak - Wednesday, September 10, 2014 - link

    DP SST 4k/60Hz should be every bit as glitch free as proper hdmi 2.0 (be careful though with the latter since some 4k TVs claiming to accept 60Hz 4k resolutions over hdmi will only do so with ycbcr 4:2:0). DP SST has the advantage that actually even "old" gear on the graphic card side can do it (such as radeons from the HD 6xxx series - from the hw side, if it could do DP MST 4k/60Hz it should most likely be able to do the same with SST too, the reason why MST hack was needed in the first place is entirely on the display side).
    But if you're planning to attach your 4k TV to your graphic card a DP port might not be of much use since very few TVs have that.
    Reply
  • Solid State Brain - Wednesday, September 10, 2014 - link

    I won't get another AMD video card until idle multimonitor consumption gets fixed. According to other websites, power consumption in such case increases substantially whereas NVidia video cards have almost the same consumption as when using a single display. In the case of the Sapphire 285 Dual-X it increases by almost 30W just by having a second display connected!!

    I think Anandtech should start measuring idle power consumption when more than one display is connected to the video card / multimonitor configurations. It's an important information for many users who not only game but also need to have productivity needs.
    Reply
  • Solid State Brain - Wednesday, September 10, 2014 - link

    And of course, a comment editing function would be useful too. Reply
  • shing3232 - Wednesday, September 10, 2014 - link

    well, AMD video card have to run higher frequency with multiscreen than with a single monitor Reply

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