I have a cheap ONN Android TV box I've used for months connected to my TV through HDMI. The sound randomly quit working 2 days ago and I cannot find the solution. If I pull up Netflix/YouTube through the actual TV apps the sound works fine, just not when used through the TV box. I've tried using the different HDMI ports as well with no luck.
Is there a setting I could've messed up, or could it just be the HDMI cable? Video still works fine through HDMI as well, just no sound. I don't have a 2nd HDMI handy to test that theory though.
Try checking the ATV box's audio settings to make sure that nothing has changed, if a audio mode that is not supported by your TV is being used, you can end up with no sound.
It that doesn't work, then you could try the good old standbys and first restart the ATV box, and if that doesn't work, try factory resetting it, the same goes for the TV itself.
You could try reversing the HDMI cable, to see if that makes any difference, sometimes unplugging/plugging a cable in and/or flexing it, can "fix" things.
I hope this made sense and was helpful.
Best wishes and good luck!