My Windows 10 version is 1709 (Fall Creators Update), so it should have the capability.
Unfortunately the flags had no effect and still couldn't use the hardware capabilities. What I noticed is that when the video is in full screen, the GPU Processing usage is significantly reduced and the Video Processing increases to numbers close to Google Chrome.
What I can be sure is that hardware decoding capabilities exist and work on both Windows 10 and Xubuntu 17.10, they only aren't being used.
Regarding audio difference on Xubuntu, the best word I could find to define the sound is "muffled". I have noticed this difference on every file with audio encoded using opus. To encode I use, for example:
ffmpeg -i INPUT -acodec libopus -application audio -b:a 320k -vbr on -f ogg -flags +global_header OUTPUT
This is very noticeable with high frequency sound, some instruments become completely inaudible. Maybe a voice optimization which degrades sound fidelity?
I face (almost) the same problem here. Things broke on version 49 because opera decided it can follow the theme's colors for fonts... and only for the fonts.
Debian testing x64, opera stable 49, openbox and numix as the theme.
Go to Opera's menu (just tap Alt or click the regular menu button). On the Page submenu the first item should be Fullscreen - see if that works. Otherwise we'll have to see if the keyboard method that Windows uses works on your desktop ...
Hey @furret29, I'm glad you found the issue. I had read something about a problem with Chrome and Gnome keyring, but thought you weren't affected (I was mislead by your using XFCE).
Thanks for sharing your findings.