Sound but not Video when using Opera

[quarkslot]

Since I moved from 8.10 to 9.04 (clean install, not upgrade) I can hear but no longer see video clips on some websites, YouTube and the BBC are examples.

However on websites which have embedded YouTube clips, like emusic.com, the same video plays without any problem.

I've gone through the usual steps for Opera to check the plugin files are installed in the right locations but cannot get it to work.

Any suggestions?

Thanks

Nick