no sound on video

I have an Apple TV 4K and just today it has stopped playing sound through tv speakers when playing video.

all the sound effects when navigating the apps work

music plays sound no problem

if I play a music video in the Music app I can see the video but no sound, however when I press the menu button the sound from the video plays even though I’m not focused on the video any more.

when I select the video as full screen the sound stops

my hardware configuration has not changed for the last 2 years and has worked fine every night until today.

i have restarted AND unplugged the Apple TV to no avail

interestingly, it plays fine on other sources except tv speakers.

The box is connected to TV via HDMI. same cable for last 2 years

please help