iPhone AVAudioPlayer stopping background music

Note: The AudioSession API has been completely deprecated in iOS 7.0

You can't run AVAudioPlayer and the iPod player or MPMusicPlayer or MPMoviePlayer at the same time, without doing a bit more work. If you want easy, then use Audio Toolbox's System Sounds.

If you want to do some extra work, then you should look at Audio Sessions:

kAudioSessionCategory_UserInterfaceSoundEffects For sound effects such as touch feedback, explosions, and so on.

Equivalent to the kAudioSessionCategory_AmbientSound category, which you should use instead. The kAudioSessionCategory_UserInterfaceSoundEffects category is deprecated in iPhone OS 3.0.

kAudioSessionCategory_AmbientSound For long-duration sounds such as rain, car engine noise, and so on. It is also for “play along” style applications, such a virtual piano that a user plays over iPod audio.

When you use this category, audio from built-in applications, such as the iPod, mixes with your audio. Your audio is silenced when the Ring/Silent switch is set to silent or when the screen locks.

Basically, every app is assigned an audio session which is modelled as a singleton class which you can get at application launch and set parameters to. The way I fixed the same problem was through a single line of code placed at applicationDidFinishLaunching:

Objective-C:

[[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryAmbient error:nil];

Swift 2/3:

try! AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryAmbient)