Yeah I can't get YouTube videos to play with SVP at all. I copy the YouTube link, and it will load for a second but do nothing 
EDIT:
I found the problem! It turns out that it was the latest Nvidia drivers was interfering with SVP.
Here is how I fixed it:
Go to Nvidia Control Panel > Manage 3D Settings > Global Settings
Go to "Background Application Max Frame Rate"
Set it to "OFF"
Apparently the latest Nvidia Drivers automatically enabled this setting to 30fps, limiting apps like SVP and Lossless Scaling. Hope this helps someone!