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H.265/HEVC

That “now” is the ultimate subject of our column; it’s H.265, or HEVC, for High-Efficiency Video Codec (the instincts of the ITU’s naming committee are a reminder of how clarity is occasionally at the expense of creativity, for better or worse). The standard was approved in April 2013. Putting very simply what H.265 does: it improves compression efficiency by up to 50% over AVC without perceptible quality loss, opening the door for storing content at 4K/Ultra HD-level resolution on mobile, streaming, and physical-media applications while keeping bandwidth usage and processing times reasonable. Improvements to the process and extensions to the codec will continue to boost quality and lower bitrate, similarly to H.262 and H.264.

To that end, H.265 pulls a lot of its structural makeup from H.264, and several features have been simplified. Most, however, are geared toward streamlining more complex coding work. For example, H.264 utilized a method of spatial prediction using pixel values from adjacent decoded blocks in order to fine-tune its image, and it did this with a total of eight directional modes. To visualize this, picture three rows of three dots each. The dot in the center is the pixel asking for “hints” as to prediction values; the eight dots surrounding it are what provide those hints. H.265 utilizes the same basic scheme, but with 35 directional modes instead of eight; this means there’s basically more than four times the resources for that central dot to pull information from. It’s picking a subject from one encyclopedia versus picking a subject from the Britannica Global Edition.

H.265 utilizes thirteen levels of encoding; with the available bitrates observed, Levels 5 and 6 and their derivatives are likely to be the most popular during the first phase of the codec’s lifespan, offering displays of 1080p at 128-300 frames per second, 2160p at 30-120 frames per second, and 4320p at 30-120 frames per second, depending on the level and derivative. There are three profiles for HEVC, consisting of a standard “Main” profile (8 bits, 4:2:0 chroma sampling); a “Main 10” profile (10 bits, 4:2:2 chroma sampling with a bitrate reduction of 5% over the Main profile, and Main Still Picture, which is a subset of the Main profile used for still image coding. There are additional profiles in development, including profiles for 12-bit decoding and 4:4:4 full chroma sampling.

What we see with the H.26x standard, cultivated chiefly through H.262, 264, and 265, is a codec given toward evolution rather than redefinition. A trend toward increased coding efficiency is the clearest improvement here, with the same general architecture precipitating, on average, a halving of bitrate for equivalent video quality every 10 years over the past three decades. The trends going into the future will focus on further improvements to compression efficiency and spatial resolution. It’s worth noting that most of the efficiency tests conducted for H.265 (as of 2014, at least), were conducted with HD content (720p or 1080p), despite one of the stated goals of the format being to realize visuals beyond high definition (I bet the original packaging for the first wave of Blu-ray discs are feeling the crushing weight of that dated hyperbole now, and no, I will not let it go). Tests of H.265 with 4K content at 24 and 30 frames per second have been conducted since, and the format has been shown to handle the visual requirement easily. Results for greater resolutions and higher detail is something baked into the H.265 mission statement, which should afford the codec a greater degree of permanence and flexibility.

Ultimately, Ultra HD is another stepping-stone; the ultimate goal here is, I assume, total perceptual immersion into the atmosphere of whatever film or event you’re watching. The implications of this are varied; the mind reels at the thought of being much closer to anything made by Zack Snyder or Michael Bay, for example. I’m reminded of The Pedestrian, a Ray Bradbury short story that I read all the way back in middle school. The story is narratively about Leonard Mead, a man in a city of millions who takes walks outside in total solitude. Everyone else stays inside, watching TV on giant wall screens. I don’t think we’ll get to that point; HDTV is still at a spotty-enough penetration rate as far as the market goes to invalidate much threat of an entirely disconnected society. Besides, it’s far more likely that we’d just stay buried in our smartphones.

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