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H.263: Reengineered videoconferencing and early mobile applications

We won’t spend much time on H.263; it’s an important intermediary step between the H.262 standard and the relative game-changer that was H.264, and it was crucial to the advent of streaming video sites that form one of HD cinema’s multiple arms, but it doesn’t have much to do with HD cinema itself directly; instead, H.263 was mostly about improving compression efficiency and improving the scalability of video quality. The codec is Web-oriented in a way that its previous incarnations were not. H.263 was never going to be used as a standard for physical media or home entertainment; its widest audience was going to be found much more in “new media” - an ethereal concept in the mid-1990s when it was established, and still slippery and insubstantial as a general term ten years later. Perhaps its biggest “get” as far as acquisition was its use in encoding Flash videos for YouTube and MySpace (mentioning the latter should let you place the acquisition in a fairly specific time frame).

H.263 also includes several improvements to predictive encoding; like H.262, it possesses B-frames as a way to retain maximum visual information at minimum storage space. It also incorporates layering via extensions, which was a boon to scalability. As we mentioned, scalability refers to the ability of a video to sustain a certain resolution, while having the ability to intelligently degrade video quality depending on bandwidth, vehicle, or provider choice. Layering is a huge aspect of scalability in its modern form, and you can identify it in just about any current type of subscription media. Netflix is probably the easiest to spot it on, where it’s pretty frequent to start up a movie or show and behold a choppy, blocky image that quickly refines itself and gains clarity and resolution. Each instance of image improvement is essentially a layer being applied to the base image, changing the acceptable protocol and bitrate depending on the scenario. In this way, it’s not dissimilar from MPEG-2’s levels.

H.264

H.264 is a product of the MPEG-4 video standard; it is also known as MPEG-4 Part 10, or by the acronym AVC (Advanced Video Codec). Put simply, it is the reason we have the video we do on Blu-ray discs, computers, tablets, and smartphones. It’s the underpinning of HD in the home, of contemporary Internet streaming video, and of mobile services. But for the final segment in this column, it is the only standard capable of displaying content at Ultra HD-level resolution.

There are a number of core enhancements inherent to H.264 that set it above its predecessors; chief among them is the targeted reduction in bitrate and the compensation in bitrate reduction with more sophisticated means of arranging each frame. A big component of this arrangement is the introduction of variable block sizes. We talked about blocks already; the H.26x standard is built on the foundation of luma and chroma blocks. With H.264, these blocks can assume varying shapes and proportions in accordance with what the predictive framing needs require. This results in a savings of approximately 15% in terms of bitrate, without a discernable compromise in quality.

H.264 was provided an extension in 2009 to allow for multiview applications, a fancy way of saying that it accepts coding of content acquired from multiple cameras; this was usable for a predicted boom in 3-D stereoscopic films. There are several other instances of increased efficiency with the H.264 codec - deblocking applications for reducing the amount of macroblocking without losing detail in the image, weighted and quarter-pixel predictive capabilities for P and B frames in the image - but the main takeaway from the standard is the enormous leap forward it brought for HD in the home, and for paving the way to what’s here now.

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