So I have tried something similar using information from an older post about linkURL. I link to a little html file which has the <video>  code very similar to what you show above (I just add autoplay). Works great, starts the video in a new tab. All good ... except one thing. If the gallery is in full screen mode, the video link changes tabs away from the gallery. When you close that tab, in Chrome at least, you return to the splash page. Like there's an implied "esc" when you change tabs, which makes sense. Could be user error, I'm not an html or javascript expert. But if this is expected behavior, I'm wondering if some sort of popup is the answer, but not sure if it's possible to get anything more complicated than a filename in linkURL...

Thanks!