Yes, I have a somewhat better idea of how to do it UI-wise, but it is a bit more complicated/depends on something else. The idea is to do it directly in the (nonexistent!) layer controls. I filed to reflect the missing feature dependency for this to happen.

There would be a nice Record button on audio layers, and when the user clicks on it,
- the timeline starts playing at the playhead and a vumeter is shown on the layer controls
- the sound is recorded and you can see a clip growing "in real time" on the timeline
- if the user pauses playback, it pauses the recording too
- if the user clicks the Record button again, or moves the playhead, it stops the recording.

Codec preferences and whatnot should probably go in the application's global preferences.

Advantages of this approach is that it's direct manipulation, and it doesn't require showing an additional dialog over the UI (I know that the pitivi devs prefer to avoid those).

Now, that would probably mean that 1) devs agree with my idea :)   2) you could implement bug #632319 before tackling #572449, if that's the case.