the sound is lost when program run in the background

[Joneshong]

It works for me.

How can I keep Audio from losing focus when not in Editor?

This has been moved to the Engine.ini file as of 4.6: GConfig->GetFloat(TEXT("Audio"), TEXT("UnfocusedVolumeMultiplier"), UnfocusedVolumeMultiplier, GEngineIni); In the DefaultEngine.ini or any of the Engine config files where you would need to change this just set: [Audio] UnfocusedVolumeMultiplier=1.0