Why is the volume low while streaming?
You can increase the volume by using the volume keys on your keyboard.
Usually this issue is easily fixed by restarting the AirPlay device and router. If that didn’t help, restart Porthole and finally your Mac.
If you’re using an Apple TV and have updated to software version 6.0 or higher, make sure you update Porthole as well. At least to version 1.4.4.