Netflix does not play video sound OK

I can login to Netflix and it plays trailers when I select a title it starts to run and after a couple of seconds I lose video but keep any text in the program, black screen. when I hover over the time line I can see the thumb nails. I have cleared Netflix website data but still the same. I can run Netflix on my iPhone and have downloaded Chrome to my iMac and that works as it should.

Latest updates installed 2 days ago

iMac Retina 4K 21.5 inch 2017