The battles over video codecs – in which high quality mobile video has been an increasingly important consideration – have become a “bloodbath” in recent years, according to Fabio Murra, SVP of products and marketing at video compression specialist V-Nova.
In this race, the main contenders are AV1 and HEVC (or H.265, the successor to the
ubiquitous H.264 or MPEG-4). But a dark horse in the picture, LCEVC (low complexity enhancement video coding), also known as MPEG-5 part 2, provides a different approach. It specifies a data stream structure made up of a base stream (decodable by a hardware decoder) and an enhancement stream (which can be processed in software). It can act as an enhancement to any of the main codecs including AV1 and HEVC.
Murra said, in the virtual version of the National Association of Broadcasters (NAB) event: “Adopting a multi-codec strategy is not necessarily easy. You need to think about what to deploy, where to deploy, and when to deploy.”
He believes there are three main decisions to make – regarding compression performance, running costs, and compatibility of the ecosystem. LCEVC promises to address all three, but of course complex questions remain about the low complexity standard.
Roughly, every generation of video codec halves file size (compression efficiency) and increases the time to encode (computational complexity) by between eight and 10 times, according to Murra, but typically with the caveat of computational costs rising by an order of magnitude higher.
“This is really the target and rationale behind LCEVC, to impact both of these dimensions,” he said, describing the 2018 proposal from MPEG, which simply required a codec-agnostic tool capable of enhancing any codec to a compression performance close to its next generation, with device compatibility and without breaking anything. In other words, a codec with low enough complexity to be deployed in software, that can enhance – not replace – existing codecs.
The low complexity part of LCEVC is demonstrated by the use of fewer encoding techniques than other codecs. HEVC, for example, uses over 100 tools and techniques for compressing images, compared to LCEVC which uses less than 10 techniques across the two sublayers – including entropy decoding, including inverse quantization, inverse transform, and smoothing filter.
Results of a recent test show LCEVC x265 winning against native x265 in 99% of the clips on Netflix’s VMAF (Video Multi-method Assessment Fusion) quality metric, and 61% on PSNR (peak signal-to-noise ratio). Here, the combined LCEVC-HEVC stream was lighter to encode and decode than the native format at same resolution.
As well as results showing impressive improvements in QoS, arguably the most alluring figure is that LCEVC can reduce encoding and CDN costs by up to 50%. There are more than just lab tests though, with early implementations out there in the form of libraries available for Windows, Linux, and ARM-based (Android, iOS) devices, and of course the V-Nova platform itself.
As for the all-important commercial encoder, Murra could only say commercial deployments supporting LCEVC were “coming soon”. What remains uncertain is the dreaded royalty scheme. Huawei, Samsung and Qualcomm have all thrown weight behind the recently approved essential video coding (EVC) standard as part of MPEG-5 Part 1 and the three tech titans recently reassured that they will offer “fair” patent royalty terms, for which licensing terms need to be published within two years.