Approximately after Google has announced that Hangouts is going to use Peer-to-Peer connections via WebRTC for voice and video, video calls have stopped working in HTML5 mode.
It shows some generic error for a moment, and offers to install the plugin.
If you have disabled NPAPI plugins completely, like I did, for security reasons, there is no way to use Hangouts for video calls at all.

Reported as DNA-49795

Since we don't have the flag that disables the "new" compositor-driven rendering path for video elements. I'm having the problem with YouTube HTML5 player.
If you play the video and start hovering your mouse cursor above any link (relevant videos, channel name, etc) you'll get huge frame drops. Enable 'stats for nerds'. I began to experience this problem when the new rendering path has been implemented. Then I disabled it in 'opera:flags' to make video playback smooth again. But now there's no option to disable it, and the video stutters every time I scroll or move the mouse in wrong places.

Reported as DNA-49794

Google Hangouts have stopped working after this update... There is no video, only black screen...

I have the same behaviour in my mac version. Is there any bug report for this?

DNA-20467

Google Hangouts have stopped working after this update... There is no video, only black screen...