Sound stopped in Safari 10.1.2 in Yosemite

[PaulRanger2]

Sound has suddenly stopped in Safari (while watching YouTube videos). I have tried the 'command option P R' restart option - to no avail. I've opened iTunes, played a song showing that the internal speakers work fine, adjustable by the F11 and F12 keys. I am running Yosemite 10.10.5 on an iMac 21.5" )late 2009). Has anyone experienced and corrected this OS X malfunction before?

Sincerely, PaulRanger2.

 

[Riwam]

It may not be the same situation but here my experience with a Yosemite hacked using MacPostFactor in an Early 2008 Macbook.
Whenever Apple releases some safety update my mac looses sound.
With the Kext Utility to be found in the web I reinstall the Apple HDA Kext and after rebooting, the internal mike and speakers work again.
Ed