DEFINITION January 2022 – Web


O ne day, memory cards high-dynamic-range images, uncompressed. That day hasn’t yet arrived – at least not for most of us. Codec design is a wonderful example of engineering compromise, balancing computer processing power, storage space and image quality. Performance improves continuously, but now just one piece of mathematics does the lion’s share of video compression. Its proper name is Advanced Video Coding, but most of us have encountered it as H.264 – part ten of the MPEG-4 standard – in every form, from ultra low- will be big enough to store all our high-resolution, high-frame-rate and bandwidth videoconferencing to high-level cinema origination. It comes in various guises. AVC-Intra and AVC-Ultra are Panasonic’s configurations, appearing in the VariCam series and AU-EVA1 – handling 4K, 4:4:4 material at 12 bits per pixel. Exactly how AVC data is handled depends on the application, and the standard gives manufacturers options to achieve a useful balance of quality, workload and file size. Turning off the more complex encoding techniques makes the material easier to encode and decode, and AVC will handle it down to low bit rates, as in Panasonic’s portable AVC-Proxy. The standards describe a series of profiles and levels. Sony calls its

high-end version XAVC, which has been used in professional cameras since the F5 series – and is often described in terms of its bit rate. The top-end Class 480 operates at 480Mbps at 24, 25 or 30fps; or 960Mbps at 50fps or more. XAVC uses AVC’s High Profile and level 5.2, which allows DCI 4K at 60fps, up to 12 bits deep. By comparison, the more compact AVCHD – developed jointly by Sony and Panasonic – uses High Profile at level 4.2, limiting resolution to 2K at 60fps. AVC provides a huge variety of options, although all of them should be understood by a well-written decoder intended to handle MPEG-4 part ten material. With AVC having been incumbent for a while, we might expect to see a sequel. One does exist: High Efficiency Video Coding or, with great originality, H.265. HEVC achieves perhaps twice the quality for a given file size, in exchange for extra mathematical effort. It’s found in cameras such as Panasonic’s compact HC-X2000, which packs 4K, 10-bit pictures at 60 frames into a package that weighs under a kilo. That’s impressive. Cramming in the hardware to handle that, and conventional AVC for video streaming, is even more astounding. To say that AVC and its brethren have revolutionised both acquisition and distribution of digital video barely hints at the extent of its influence. Although, it

The salt mines Film can’t be copied without generation loss, but digital images can. That ability to make backups is no bad thing, given that flexibility and complexity are often interchangeable. Hedge’s titular product is a backup and archiving utility, supported by a range of tools to deal with verification and reliability checking, as well as backup to LTO with the Canister utility. As one of the last data tape formats on the planet, LTO remains about the only option for long-term secure archiving. Hedge can also help keep things organised on shared storage, as part of the Postlab suite. Its most codec-relevant tools actually come via its acquisition of Divergent Media. EditReady is a transcoding and rewrapping tool designed to solve compatibility problems with codecs and colorimetry.

COMPLEX Sony Venice 2 (above); Panasonic VariCam LT (below)

was not solely intended to behave as a mezzanine codec like ProRes. By switching off the inter-frame compression, we can make AVC behave more like ProRes, but Apple’s codec will probably always be a little easier on the silicon. The mathematics underlying ProRes are well established. It’s a fantastic illustration that simply having a standard is more important than it being hugely advanced – especially if we “Codec design is a wonderful example of engineering compromise, balancing computer processing power, storage space and image quality”

47. JANUARY 2022

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