Sorry if this has already been suggested (I did a search for "mp3" and found nothing), but this is something that could help keep the size of custom maps down by quite a bit.

But, my suggestion is an entity for playing mp3 music within HL/BB in a similar manner that Natural-Selection handles mp3s (or just an ambient_generic). Just an entity where you can either define a radius or flag it as a global sound as well as define whether it loops or not. With this, mappers wouldn't have to worry about 20 meg .wav files if they wanted to add music or large ambient sound (TV or radio broadcast, etc.) to their map.

Any and all comments are welcome.