Step 1) After the vive is setup, go to steam library and find the virtual desktop app.
2) Launch the app and a screen should pop up on the desktop (Not in VR) From this screen press the videos tab on the top to access the 360 video page.
3) Once you’ve entered this page you need to open chrome or any web browser and find the link to the 360 youtube video you want to view. Once found, copy the url to the clipboard by highlighting the url right clicking and pressing copy.
4) Back on the virtual desktop page, press the PasteURL button (Circled below) and the 360 video should begin playing automatically in the htc vive headset after the video has been downloaded.