The document discusses the next-generation video codec H.265 (HEVC), highlighting its ability to produce high-quality 4K video while significantly reducing file sizes compared to H.264. Early tests show that H.265 can achieve close to 50% bandwidth savings at certain settings, and its performance is improving with support for parallel computing. Although current support is limited and it requires more computational power, H.265 is poised to replace H.264 as the dominant codec for advanced video applications.

1. Technical Insights - Embedded
Next Generation 4K Video Codec Experience – Ultra HD
The next-generation High Efficiency Video codec (HEVC), H.265, has hit a major public milestone, the
x265 encoder is already impressively parallelized and supports all of the major instruction sets including
AVX/AVX2 and FMA3/FMA4.
There are lots of discussion about H.265 and next-generation video encoding technologies, but this is
the first time we’ve had the chance to sit down with a next-generation encoder (albeit a pre-alpha
version) to examine both performance and video quality. We’ve put together a comparison of both
video quality and stream encode sizes versus H.264, as well as a quick look at performance across Sandy
Bridge-E, Ivy Bridge, and Haswell.
The benefits of H.265
H.264 has been a huge success. It’s a flexible codec standard that’s used by streaming services, satellite
providers, and for Blu-ray discs. It’s scaled remarkably well since it was first proposed and is capable of
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2. Technical Insights - Embedded
handling 3D, 48-60 fps encodes, and even 4K. The Blu-ray disc standard doesn’t currently include
provisions for some of these technologies, but the H.264 codec itself is capable of handling them.
The problem with H.264, however, is that while it can handle these types of encodes, it can’t do so while
simultaneously keeping file sizes low. A new standard is necessary to push file/stream sizes back down
while driving next-generation adoption, and that’s where H.265 comes in. It’s designed to utilize
substantially less bandwidth thanks to advanced encoding techniques and a more sophisticated
encode/decode model.
Unlike H.264, which can extend to cover 4K television but wasn’t designed with the feature in mind,
H.265 was built to match the capabilities of future screens and includes support for 10-bit color and high
frame rates. This is early days — support and capability of the current alpha are limited to 8-bit color
and YUV output, but we still wanted to take the alpha technology out for a spin. Armed with a freshly
compiled version and some test clips, we set out to see what we could build.
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3. Technical Insights - Embedded
First up — file sizes. What we’re comparing here is actually the size of the elementary video stream.
Note that these are video streams only — audio isn’t encoded in either instance. Encode sizes were
defined by the quantizer setting, with lower q-values equaling a higher quality (and larger file size). The
base encoded file is 500 frames of a 1.5GB, YUV 4:2:0 file at 50 fps. The elementary stream file size is
used for comparison here because it represents what’s transmitted to the decoder to create the final
output. We’re working with elementary streams because, at this stage of the project (pre-alpha), the
decoded video file always comes back at 1.5GB, regardless of the stream quality used to create it.
This gives a good basic idea of what sorts of benefits H.265 can offer compared to H.264. While it’s not
hitting 50% bandwidth savings in most cases, it’s close — quantizer 24 is 57% the size, q=30 is 59%, and
q=40 is just 47%. Granted, at a quantizer of 40, the final output is wretched — but it’s wretched at less
than half the bandwidth.
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4. Technical Insights - Embedded
Performance & image quality
The next area we wanted to consider was performance. H.265 is known for taking more horsepower to
encode and decode than H.264, though the team developing the standard continues to emphasize the
role of parallel computing in speeding the encode/decode process. It’s implied that OpenCL support will
materialize sooner, rather than later, which means initiatives like AMD’s HAS could get a boost from
x265 support early in 2014.
Right now, we’re limited to CPU support, but MultiCoreWare spokesperson Tom Vaughan emphasized
that the team has already been working on strong multithreading. We decided to test the alpha decoder
using Sandy Bridge-E, Ivy Bridge, and Haswell. We experimented with different levels of parallelization
but settled on options that stuck to the number of physical cores in a system (6, 4, and 4). HyperThreading was enabled, but setting for 12/8 - thread parallelization actually increased encode time
slightly.
HDMI 2.0 (the name going around the industry, despite the HDMI forum's decision to do away with
version numbers for all HDMI products) is going to be ratified soon, and will apparently simply double
the operating frequency of the controller / PHY to provide enough bandwidth to send across
uncompressed 4Kp60 video. The high cost of current 4K solutions is already a deterrent, and if one is
hesitating to jump in right now, these facts should serve as an incentive to wait for some more time.
Contrary to popular belief, there is really no dearth of 4K content since most professional videographing
solutions have been 4K capable for a number of years. It is a simple matter of bringing that content in
the right format to the end-consumer. H.264 emerged as the codec of choice (and replaced MPEG-2 due
to better compression efficiency) when moving from SD to HD. However, both H.264 and MPEG-2 coexist in the Blu-ray standard for HD content. Similarly, H.265 (HEVC) is expected to become the codec of
choice (and replace H.264 due to better compression efficiency) when moving from HD to 4K. However,
consumers can expect a lot of the initial 4K end-user content to be in H.264 format (such as the current
4K videos on YouTube or the 4K videos being shot on the GoPro Hero 3 Black). All said, a future-proof 4K
solution should have the capability to decode 4K content in both H.264 and H.265 (HEVC) formats.
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5. Technical Insights - Embedded
The parallelization performance looks good — Sandy Bridge-E, with six cores, is somewhat ahead of Ivy
Bridge with four. Similarly, Ivy Bridge is beaten out by Haswell, thanks to the new core’s AVX2 support
and better performance characteristics. Compared to x264, even on the –very slow preset, x265
encodes take noticeably longer — our Ivy Bridge 3770K encoded the same file in H.264 in 129 seconds
as compared to 247 seconds for H.265. Keep in mind, however, that this is very, very early software.
Of more interest is the quality question — how does the H.265 output compare to the uncompressed
original? We chose a basketball clip because, at 50 fps, it’s full of the sort of fast motion that often gives
encoders fits. H.265’s smaller sizes won’t be worth much if the final output isn’t as good.
To that end, here’s the original uncompressed YUV output, the H.265 encode at q=24, and the H.264
output at q=24. Click on each image to enlarge it.
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6. Technical Insights - Embedded
Original uncompressed
H265 Q=24
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7. Technical Insights - Embedded
H264 Q=24
The variance here is minimal. The hardwood floor underneath the leaping player is slightly less blurry in
the H.264 variant, but the H.265 image quality is phenomenal considering it’s half the size. What about
lower qualities? Here’s H.265 and H.264 at q=30; H.265 is first.
H.265 Q=30
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8. Technical Insights - Embedded
H.264 Q=30
At q=30 (file sizes of 6.39MB and 10.87MB), the H.265 video stream is arguably better than the H.264
encode stream. We’re not trying to claim this is an absolute — as always, encode settings matter a great
deal and are sensitive to tweaking. But after waiting more than a year for H.265 to break cover, it’s clear
that the new standard is going to offer what its proponents have claimed.
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Encode/decode support, meanwhile, is already going to be possible on a vast range of products. Modern
CPUs are more than capable of decoding H.265 in software, OpenCL support is coming in future
iterations, and hardware GPU support, while not formally guaranteed by AMD, Intel, or Nvidia for nextgeneration products, is a mid-term certainty. All three companies have previously leapt to include
advanced video pipelines in their products — as the H.265 presentation notes, video is something that’s
become ubiquitous across every type of device.
Long-term, H.265 will likely succeed H.264’s position as the premier solution for advanced video, though
that may depend on whether or not battery consumption while decoding can match H.264’s levels in the
long term. That’s something we’ll only be able to evaluate once hardware is available, but for now we’re
optimistic. H.265’s explicitly parallel model should map well against multi-core devices of the future.
Source: Extremetech.com
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