Yesterday released Opera 30 stable enables Media Source Extensions (MSE) & H.264 support in the browser, which allows users to watch 60FPS videos on YouTube. After upgrading from Opera 29, some users noticed YouTube videos not playing in their browser. The Opera desktop team is working on a fix, meanwhile try this workaround.
UPDATE: Opera has fixed this by releasing a minor update, check for updates to install it (version number is: 30.0.1835.59). Only 32-bit Windows 7 version users affected.
Fix YouTube Videos not playing in Opera 30
1. Visit opera://flags/#mse-h264-support in the browser address bar
2. Choose ‘Disabled’ from the drop down, click ‘Relaunch now’ to restart the browser.
3. Now Visit YouTube and try to play any video, it will work.
If you don’t know about this change: Recent Tabs submenu in Opera menu has been moved to Tab Menu.