When I play a video from my Photos app on my iMac. it periodically freezes and the audio continues for a couple of seconds then stops. In about 5 seconds the frozen video starts up again and fast forward's for 3 seconds and then everything plays normall for another 30-40 seconds when the abnormal behavior repeats itself. This also happens with Quick Time screen recordings. Not sure if this is related but many videos at websites turn blank white with a gray progress bar on the bottom with no audio, when I press the play arrow, I am running Sierra 10.12.1. Thanks Forummers