[Feature request] XPSNR metric as an alternative to VMAF

[gitoss]

The ab-av1 encoding helper just added XPSNR in addition to VMAF: alexheretic/ab-av1#256

XPSNR is designed to be fast, and target-quality searching seems to be a major bottleneck on av1an. The metic is like PSNR logarithic (until 'inf'), i.e. this a bit of a change vs. VMAF.

https://github.com/fraunhoferhhi/xpsnr
https://ffmpeg.org/ffmpeg-filters.html#xpsnr-1

XPSNR is supported out of the box on recent ffmpeg, so it's probably as hassle-free as it gets adding a new metric.

I suggest looking at adding XPSNR to av1an, too - either as an alternative metric (XPSNR claims to be match about the same as VMAF http://www.ecodis.de/video/helmrich_xpsnr_rev3.pdf) and/or better performance (this would require some benchmarks w/ different settings).

Thanks for considering - see the av1an feature request and code changes for details how to pull the score from ffmpeg.