  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.
