VMAF is considered by many to be the best metric to measure video compression by. I knew it was somewhat random with respect to inputs. Now I know how awful it is. Some months ago people figured out they can cheat it by just sharpening the video before compression. This doesn't mean the video looks better though. Of course, libaom implemented a sharpening filter as a preprocessor to increase its vmaf score by around 30%. Just don't use VMAF alone, ever. Provide PSNR, PSNR-HVS and SSIM as well.