update, some videos play OK, how do I tell the format of the ones that do not play/play with black picture?

I have Opera 30.0.1835.59 running on Windows7 My twitter seems unable to run Videos, can hear the sound but the movies are on a black screen. How do i fix this? It works fine on FF but as that is extremally slow at loading I prefer Opera. Chrome and IE are also No No's.