I have GuitarToolkit on my iPhone4S (iOS 5.01 – NOT jailbroken) It has a metronome feature which continues playing in the background, and also adds a red banner overlay (see screenshots) which persists on the home/lock screen and also when other apps are running. The banner is animating (background colour pulses) and it is also ‘active’ in that pressing it will return you to the GuitarToolkit app.
I know about the background audio APIs for the sound, but how does it do this banner? My first thought was local notifications, but nothing appears in notification center, and GuitarToolkit is not listed under Notifications in Settings.
My iPhone is not jailbroken and GuitarToolkit is available in the App Store, so what APIs is it using to achieve this?
The banner appears because it’s got an open audio recording session—you’ll notice that the system Voice Memos app does the same thing, as does Shazam for a moment before it enters the background and Skype when you’re on a call with the app in the background. I’m not sure of the specific API, but that’s generally what’s going on.