Hello @glenburns1, welcome to the Sonos Community!
When I mirror a movie to the TV from computer the TV defaults to TV sound.
Sounds like the HDMI-CEC protocol on your Samsung TV is not working properly. Make sure to enable the Anynet+ setting on your Samsung TV which represents the HDMI-CEC protocol for the brand.
Have a look on the Samsung Support page on how to do so : Use Anynet+ (HDMI-CEC) on your Samsung Smart TV.
You could also do a hard reboot on your Samsung TV by unplugging the power cable, wait for a couple minutes and then plug it back in.
If you are still experiencing this, you should reach out to Samsung Support.
I hope this helps.
