I have a Dell Latitude 5480.
I am perfectly happy with my switch from my old OS to Qubes OS except for DVD or HD Video playback. Video is just not running smooth.
Now there is GPU passthrough,can it help me here?
How would I go about it, when doing this for just one app qube, an app qube I intend for the sole purpose of playing dvds?
What are the security risks? Are there more risks apart from the gpu knowing what is going on on the screen including other qubes? If this is indeed the only risk, would it help, if I restrict myself to using this qube, only when running no other qubes?
Only if you have a second GPU for passing through.
…that cancels my plan for smooth dvd playback
Your machine should easily be good enough for DVD-Video playback without any hardware acceleration. I’d guesstimate 1080p30 H.264 is still fine. Try a good player:
mpv --vo=x11 --profile=sw-fast dvd://
For stereo output maybe also add
--audio-channels=stereo because (without having benchmarked this) it seems more efficient to downmix in the VM and send 2 channels to dom0 than to send e.g. 6 channels to dom0 and downmix there.