27 research outputs found
Rate-Distortion Optimization With Alternative References For UGC Video Compression
User generated content (UGC) refers to videos that are uploaded by users and
shared over the Internet. UGC may have low quality due to noise and previous
compression. When re-encoding UGC for streaming or downloading, a traditional
video coding pipeline will perform rate-distortion (RD) optimization to choose
coding parameters. However, in the UGC video coding case, since the input is
not pristine, quality ``saturation'' (or even degradation) can be observed,
i.e., increased bitrate only leads to improved representation of coding
artifacts and noise present in the UGC input. In this paper, we study the
saturation problem in UGC compression, where the goal is to identify and avoid
during encoding, the coding parameters and rates that lead to quality
saturation. We proposed a geometric criterion for saturation detection that
works with rate-distortion optimization, and only requires a few frames from
the UGC video. In addition, we show how to combine the proposed saturation
detection method with existing video coding systems that implement
rate-distortion optimization for efficient compression of UGC videos.Comment: 5 pages, 6 figures, accepted at International Conference on
Acoustics, Speech, & Signal Processing (ICASSP) 202
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
Deformable block based motion estimation in omnidirectional image sequences
This paper presents an extension of block-based motion estimation for omnidirectional videos, based on a camera and translational object motion model that accounts for the spherical geometry of the imaging system. We use this model to design a new algorithm to perform block matching in sequences of panoramic frames that are the result of the equirectangular projection. Experimental results demonstrate that significant gains can be achieved with respect to the classical exhaustive block matching algorithm (EBMA) in terms of accuracy of motion prediction. In particular, average quality improvements up to approximately 6dB in terms of Peak Signal to Noise Ratio (PSNR), 0.043 in terms of Structural SIMilarity index (SSIM), and 2dB in terms of spherical PSNR, can be achieved on the predicted frames