Horizontal lines (some kind of dithering) while playing Youtube videos

[Atak_Snajpera]

I've noticed that when video is running I get those horizontal lines on image. Lines immediately disappear when I pause video.
It looks like some kind of weird dithering effect to hide banding on image.

My setup:
Windows 7 x64, FireFox 56 , VP9 (NO GPU acceleration)
reference video
https://www.youtube.com/watch?v=JuVWs9IZIvk

Paused (no lines)
http://i.cubeupload.com/ewe6wS.png
http://i.cubeupload.com/SmYvo0.png

Playback (lines appear)
http://i.cubeupload.com/Og5e1V.png
http://i.cubeupload.com/6Huz7m.png

[huhn]

i was hoping someone that knows what going on will answer this but well...

so in my personal experience this issue only happen with firefox and when scaling is done by the HTML5 renderer. i never saw this problem with chrome and i was under the impression this has something todo with high DPI settings on windows 10.

but i can confirm your issue:
https://abload.de/img/firefox9dqr6.png

i gave up on firefox because it was impossible to play anything fluid with it when high DPI setting are used and it clearly can't handle high dpi setting that pretty much the end of my story.