Learning from the patent miss-steps of HEVC, MPEG have released MPEG-5 EVC which brings bitrate savings, faster encoding and clearer licencing terms including a royalty-free implementation. The hope being that with more control over exposure to patent risk, companies large and small will adopt EVC as they improve and launch streaming services now and in the future.
At Mile High Video 2020, Kiho Choi introduced the MPEG 5 Essential Video Coding. Naturally, the motivation to produce a new codec was partly based on the continued need to reduce video bitrates. With estimates of the video traffic share on the internet, both now and in the future all hovering between 75% and 90% any reduction in bitrate will have a wide benefit, best exemplified by Netflix and Facebook’s decision to reduce the bitrate at the top of their ABR ladder during the pandemic which impacted the quality available to viewers. The unspoken point of this talk is that if the top rung used EVC, viewers wouldn’t notice a drop in quality.
The most important point about EVC, which is in contrast to the MPEG/ISO co-defined standard form last year, VVC, is that it provides businesses a lot of control over their exposure to patent royalties. It’s no secret that much HEVC adoption has been hampered by the risk that large users could be approached for licencing fees. Whilst it has made its way into Apple devices, which is no minimal success, big players like ESPN won’t have anything to do with it. EVC tackles this problem in two ways. One is to have a baseline profile which provides bitrate savings over its predecessors but uses a combination of technologies which are either old enough to not be eligible for royalty payments or that have been validated as free to use. Companies should, therefore, be able to use this level of codec without any reasonable concern over legal exposure. Moreover, the main profile which does use patentable technologies allows for each individual part of the profile to be switched off meaning anyone encoding EVC has control, assuming the vendor makes this possible, over which technologies they are using and hence their exposure to risk. Kiho points out that this business-requirements-first approach is new and in contrast to many codecs.
Kiho highlights a number of the individual tools within both the baseline and main codecs which provide the bitrate savings before showing us the results of the objective and subjective testing. Within the EVC docs, the testing methodology is spelt out to allow EVC to be compared against predecessors AVC and HEVC. The baseline codec shows an improvement of 38% against 1080p60 material and 35% for UHD material compared to AVC doing the same tasks yet it achieves a quicker encoder (less compute needed) and the decode is approximately the same. The main profile, being more efficient is compared against HEVC which is, itself, around 50% more efficient than AVC. Against HEVC, Kiho says, EVC main profile produces an improvement of around 30% encoding gain for UHD footage and 25% for 1080p60 footage. Encoding is close to 5x longer and decoder is around 1.5x longer than HEVC.
Kiho finishes by summarising subjective testing of SDR and HDR videos which show that, in contrast to the objective savings which are calculated by computers, in practice perceived quality is higher and enables a higher bitrate reduction, a phenomenon which has been seen in other codec comparisons such LCEVC. SDR results show a 50% encoding gain for 4K and 30% for 1080p60 against AVC. Against HEVC, the main profile is able to deliver 50% coding gains for 4K content and 40% for 1080p60. For HDR, the main profile provides an approximately 35% encoding gain for both 1080p60 and 4k.
Senior Engineer & Technical Lead for Multimedia Standards at Samsung Electronics
Lead Editor of MPEG5 Part 1 Essential Video Coding