Today I read Lennart Poettering' blogpost titled "Tagging Audio Streams" where he talks about exactly this. Here's a quote from his blogpost:
...PulseAudio can enforce all kinds of policy on sounds. For example, starting in 0.9.15, we will automatically pause your media player while a phone call is going on. To implement this we however need to know what the stream you are sending to PulseAudio should be categorized as: is it music? Is it a movie? Is it game sounds? Is it a phone call stream?
Also, PulseAudio would like to show a nice icon and an application name next to each stream in the volume control. That requires it to be able to deduce this data from the stream.
The feature will be available in PulseAudio 0.9.15, so will will have to wait for Karmir Koala, since PulseAudio 0.9.15 won't land in Jaunty.
Source: Lennart Poettering