User guide

Adding Volume and Route Control

Use the MPVolumeView class to present volume and routing control for your app. The volume view provides

a slider to control the volume from inside your app and a button for choosing the output audio route. Apple

recommends using the MPVolumeView route picker over AVAudioSessionPortOverride when routing

audio to the built-in speaker. See MPVolumeView Class Reference .

Responding to Remote Control Events

Remote control events let users control an app’s multimedia. If your app plays audio or video content, you

might want it to respond to remote control events that originate from either transport controls or external

accessories. iOS converts commands in UIEvent objects and delivers the events to the app. The app sends

them to the first responder and, if the first responder doesn’t handle them, they travel up the responder chain.

Your app must be the “Now Playing” app and currently playing audio before it can respond to events. See

Remote Control Events and MPNowPlayingInfoCenter Class Reference.

Activating and Deactivating Your Audio Session

The system activates your audio session on app launch. Even so, Apple recommends that you explicitly activate

your session—typically as part of your app’s viewDidLoad method, and set preferred hardware values prior

to activating your audio session. See Setting Preferred Hardware Values (page 33) for a code example. This

gives you an opportunity to test whether activation succeeded. However, if your app has a play/pause UI

element, write your code so that the user must press play before the session is activated. Likewise, when

changing your audio session’s active/inactive state, check to ensure that the call is successful. Write your code

to gracefully handle the system’s refusal to activate your session.

The system deactivates your audio session for a Clock or Calendar alarm or incoming phone call. When the

user dismisses the alarm, or chooses to ignore a phone call, the system allows your session to become active

again. Whether to reactivate a session at the end of an interruption depends on the app type, as described in

Audio Guidelines By App Type (page 43).

Listing 1-1 shows how to activate your audio session.

Listing 1-1 Activating an audio session using the AV Foundation framework

NSError *activationError = nil;

BOOL success = [[AVAudioSession sharedInstance] setActive: YES error:

&activationError];

Defining an Audio Session

Adding Volume and Route Control