I can confirm the observations of tobiasra.

I suspect the change is the result of this discussion:


For me Opium dynamically changes priority to Normal (8) for the foreground tab, and Below Normal (6) to background tabs. Video does stutter occasionally on the configuration where Opera 12 works well.

I'm not sure how this can be resolved because in the previous situation pages overloaded with Flash could hang a PC. Perhaps like with all normal software that deals with multimedia playback, a process/thread priority setting could be added. Do not be afraid of a Preferences dialog. The browser is not exactly a media player. But if you try to combine the functionality of one into it, a large options dialog seems unavoidable, for use cases, where the browser is mainly used for semi-realtime media playback, or browsing.