This is on the nexus 7 so I'm not sure about any other devices...
Go to settings, then under Device, click sound. At the top of the menu, it will say volume, click on that. Slide the slider that says music and games and slide to 100%. After this, try your sound out on YouTube or BBC iPlayer, (doesn't really matter) and you should no longer get the message. This is how is worked for me! Hope it helped.
Go to settings, then under Device, click sound. At the top of the menu, it will say volume, click on that. Slide the slider that says music and games and slide to 100%. After this, try your sound out on YouTube or BBC iPlayer, (doesn't really matter) and you should no longer get the message. This is how is worked for me! Hope it helped.