Fix for Youtube error: 'This video is currently unavailable' - Ubuntu Chromium

Thankfully, this one's an easy fix and will presumably apply to other browsers and operating systems, as well.

I've been using Chromium as my browser for a while and everything has been great until recently, when some youtube videos wouldn't play reliably and instead would show the error:

This video is currently unavailable.

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This is apparently caused by being enrolled in Youtube's HTML5 video trial. You can enroll/unenroll from the program by visiting this link.

I had forgotten I was even using HTML5 video, so I never even considered this could be the problem. Once I unenrolled, everything works fine again. Of course, YMMV.