Provide an AirPlay Picker

The user can go to the system AirPlay picker in the iOS multitasking interface to select an AirPlay output, as illustrated in Figure 3-1. If an AirPlay output device is available, an AirPlay button appears next to the volume slider; tapping the button displays a list of available devices.

If your app plays media, you might want to provide an AirPlay output picker within your app so that the user doesn’t have to change focus. You can add an AirPlay picker to your media playback controls by using MPVolumeView, as shown in the following code snippet:

MPVolumeView *volumeView = [ [MPVolumeView alloc] init] ;

[view addSubview:volumeView];

If you have a custom media controller and don’t want to use the standard volume controller, you can add just the AirPlay picker using the following code snippet:

MPVolumeView *volumeView = [ [MPVolumeView alloc] init] ;

[volumeView setShowsVolumeSlider:NO];

[volumeView sizeToFit];

[view addSubview:volumeView];

The picker is visible only when there is an AirPlay output device available.

Send Audio Where It Belongs

Apps typically use two types of sound—app audio (such as ambient sounds, background music, and incidental noises) and system sounds (such as key clicks and alert sounds). AirPlay attempts to deliver the app audio to a remote sound system while keeping system sounds on the host, so that feedback sounds remain local to the input device.

If your app uses system sound APIs for app audio, AirPlay does not redirect them to the AirPlay-enabled sound system. The result is a less-than-optimum user experience. It is important to use system sound APIs only for system sounds. For app audio, use APIs such as AVAudioPlayer.

Provide Audio Metadata

Your audio might be playing on a big-screen home theater system or on a sound system with an LCD display. Your app gives a better user experience if you provide metadata that can be shown on the AirPlay device’s display, such as the artist name, song title, and album art.

Add metadata by passing a dictionary into the setNowPlayingInfo method of MPNowPlayingInfoCenter. The MPNowPlayingInfoCenter class is part of the MediaPlayer framework, but works with all playback frameworks, including MediaPlayer, AVFoundation, and AudioQueue.

In addition to providing the usual song information strings, you should also pass in the playback rate, elapsed time, and media item duration. The playback device can use the duration and playback rate to create a progress bar. Update the elapsed time and playback rate whenever the playback rate changes.

Respond to Remote Events

When AirPlay is in use, your media might be playing in another room from your host device. The AirPlay output device might have its own controls or respond to an Apple remote control. For the best user experience, your app should listen for and respond to remote events, such as play, pause, and fast-forward requests. Enabling remote events also allows your app to respond to the controls on headphones or earbuds that are plugged into the host device.

Use the following code snippet to receive remote events:

- (BOOL) canBecomeFirstResponder {return YES;}

- (void) viewDidAppear: (BOOL) animated {

    [super viewDidAppear:animated];

    [ [UIApplication sharedApplication] beginReceivingRemoteControlEvents];

    [self becomeFirstResponder];

}

When your app is finished playing media, let the system know that you are no longer the receiver for remote events by using the following code snippet:

- (void) viewWillDisappear: (BOOL) animated {

    [super viewWillDisappear:animated];

    [ [UIApplication sharedApplication] endReceivingRemoteControlEvents];

    [self resignFirstResponder];

}

Respond to events of the type UIEventTypeRemoteControl and the subtypes appropriate for your app. The following code snippet gives an example:

- (void) remoteControlReceivedWithEvent: (UIEvent *) receivedEvent {

    if (receivedEvent.type == UIEventTypeRemoteControl) {

        switch (receivedEvent.subtype) {

            case UIEventSubtypeRemoteControlTogglePlayPause:

                [self playPauseToggle: nil]

                break;

            case UIEventSubtypeRemoteControlNextTrack:

                [self nextTrack: nil]

                break;

...

See UIEvent.h for an enumeration of event subtypes.