Subaru 2015 BRZ Owner's Manual page 328

Condition
Audio is output, but not video (even when the vehicle
is stopped).
Neither audio nor video is output.
There are dots that are always lit on the screen.
Possible cause
The parking brake is not applied.
The vehicle ignition switch is not turned on.
At least 99.99% of the pixels on TFT panels function
correctly, but 0.01% of the pixels may not light or may
stay lit.
Action
Apply the parking brake.
Turn the vehicle ignition switch to "ACC" or "ON".
This is not a defect, so please use the device in this
condition.
Reference
Other 327