Luke,
Videos do not play if logging into Web Client, or ET web version (tv.emby.media) via external IP address. This issue just recently popped up since installing v3.0.6000. I only use external IP at work, so I just found this out. Theme songs work fine, but if I press play, or resume... nothing happens.
Will send you a log via PM.
Hope you can find the issue, watching YouTube sucks!