anyone know if it is possible to use nexus 4 speakerphone for normal audio, ie. music or video.

Welcome to Android Central! The speakerphone uses the main speaker, so it would seem to me that it already uses the same speaker that normal audio uses.
 
My speakerphone works but when I try to make a call or listen to music it makes no sound.

Sorry, I'm a bit confused. You said the speakerphone works, but it makes no sound when you make a call? When you're on speakerphone, can you hear the other person's voice over the main speaker?