5 research outputs found
Comparison of HDR quality metrics in Per-Clip Lagrangian multiplier optimisation with AV1
The complexity of modern codecs along with the increased need of delivering
high-quality videos at low bitrates has reinforced the idea of a per-clip
tailoring of parameters for optimised rate-distortion performance. While the
objective quality metrics used for Standard Dynamic Range (SDR) videos have
been well studied, the transitioning of consumer displays to support High
Dynamic Range (HDR) videos, poses a new challenge to rate-distortion
optimisation. In this paper, we review the popular HDR metrics DeltaE100
(DE100), PSNRL100, wPSNR, and HDR-VQM. We measure the impact of employing these
metrics in per-clip direct search optimisation of the rate-distortion Lagrange
multiplier in AV1. We report, on 35 HDR videos, average Bjontegaard Delta Rate
(BD-Rate) gains of 4.675%, 2.226%, and 7.253% in terms of DE100, PSNRL100, and
HDR-VQM. We also show that the inclusion of chroma in the quality metrics has a
significant impact on optimisation, which can only be partially addressed by
the use of chroma offsets.Comment: Accepted version for ICME 2023 Special Session, "Optimised Media
Delivery
Filling the gaps in video transcoder deployment in the cloud
Cloud-based deployment of content production and broadcast workflows has
continued to disrupt the industry after the pandemic. The key tools required
for unlocking cloud workflows, e.g., transcoding, metadata parsing, and
streaming playback, are increasingly commoditized. However, as video traffic
continues to increase there is a need to consider tools which offer
opportunities for further bitrate/quality gains as well as those which
facilitate cloud deployment. In this paper we consider preprocessing,
rate/distortion optimisation and cloud cost prediction tools which are only
just emerging from the research community. These tools are posed as part of the
per-clip optimisation approach to transcoding which has been adopted by large
streaming media processing entities but has yet to be made more widely
available for the industry.Comment: Camera-ready version of BEIT Conference at NAB 202
Direct Optimisation of for HDR Content Adaptive Transcoding in AV1
Since the adoption of VP9 by Netflix in 2016, royalty-free coding standards
continued to gain prominence through the activities of the AOMedia consortium.
AV1, the latest open source standard, is now widely supported. In the early
years after standardisation, HDR video tends to be under served in open source
encoders for a variety of reasons including the relatively small amount of true
HDR content being broadcast and the challenges in RD optimisation with that
material. AV1 codec optimisation has been ongoing since 2020 including
consideration of the computational load. In this paper, we explore the idea of
direct optimisation of the Lagrangian parameter used in the rate
control of the encoders to estimate the optimal Rate-Distortion trade-off
achievable for a High Dynamic Range signalled video clip. We show that by
adjusting the Lagrange multiplier in the RD optimisation process on a
frame-hierarchy basis, we are able to increase the Bjontegaard difference rate
gains by more than 3.98 on average without visually affecting the
quality.Comment: SPIE2022:Applications of Digital Image Processing XLV accepted
manuscrip