在iphone上播放背景音频

Question

在应用程序运行时如何播放背景音频？

谢谢。

Answer 1

好的。 这是iOS4和iOS5上的背景声音解决方案（绝对适用于iOS 5.0.1），我只使用AVPlayer进行了测试。 它也可能适用于MPMusicPlayerController。

必需的框架：

• AVFoundation.framework
• AudioToolbox.framework

在Info.plist ，对于密钥UIBackgroundModes ，添加audio 。

在MyAppDelegate.h ：

• 参考<AVFoundation/AVFoundation.h> ＆ <AudioToolbox/AudioToolbox.h>

• 实现协议AVAudioSessionDelegate ：

   @interface MyAppDelegate : NSObject <UIApplicationDelegate, AVAudioSessionDelegate> 

• 定义一个方法ensureAudio ：

   // Ensures the audio routes are setup correctly - (BOOL) ensureAudio; 

在MyAppDelegate.m ：

• 实现ensureAudio方法：

   - (BOOL) ensureAudio { // Registers this class as the delegate of the audio session (to get background sound) [[AVAudioSession sharedInstance] setDelegate: self]; // Set category NSError *categoryError = nil; if (![[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:&categoryError]) { NSLog(@"Audio session category could not be set"); return NO; } // Activate session NSError *activationError = nil; if (![[AVAudioSession sharedInstance] setActive: YES error: &activationError]) { NSLog(@"Audio session could not be activated"); return NO; } // Allow the audio to mix with other apps (necessary for background sound) UInt32 doChangeDefaultRoute = 1; AudioSessionSetProperty(kAudioSessionProperty_OverrideCategoryMixWithOthers, sizeof(doChangeDefaultRoute), &doChangeDefaultRoute); return YES; } 

• 在application:didFinishLaunchingWithOptions:方法中，在分配根视图控制器之前，运行[self ensureAudio] ：

   - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { // Configure audio session [self ensureAudio]; // Add the navigation controller's view to the window and display. self.window.rootViewController = self.navigationController; [self.window makeKeyAndVisible]; return YES; } 

• 实现AVAudioSessionDelegate方法，如下所示：

   #pragma mark - AVAudioSessionDelegate - (void) beginInterruption { } - (void) endInterruption { // Sometimes the audio session will be reset/stopped by an interruption [self ensureAudio]; } - (void) inputIsAvailableChanged:(BOOL)isInputAvailable { } 

• 确保您的应用继续在后台运行。 如果你愿意，可以使用ol' [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler] ，但我认为有更好的方法。

• 播放实际音频（注意我正在使用ARC，这就是为什么没有release呼叫）：

   NSURL * file = [[NSBundle mainBundle] URLForResource:@"beep" withExtension:@"aif"]; AVURLAsset * asset = [[AVURLAsset alloc] initWithURL:file options:nil]; AVPlayerItem * item = [[AVPlayerItem alloc] initWithAsset:asset]; __block AVPlayer * player = [[AVPlayer alloc]initWithPlayerItem:item]; __block id finishObserver = [[NSNotificationCenter defaultCenter] addObserverForName:AVPlayerItemDidPlayToEndTimeNotification object:player.currentItem queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification *note) { [[NSNotificationCenter defaultCenter] removeObserver:finishObserver]; // Reference the 'player' variable so ARC doesn't release it until it's // finished playing. player = nil; }]; // Trigger asynchronous load [asset loadValuesAsynchronouslyForKeys:[NSArray arrayWithObject:@"tracks"] completionHandler:^{ // Start playing the beep (watch out - we're not on the main thread here)! [player play]; }]; 

• 而且它真的很棒！

Answer 2

如果您还使用您的应用程序进行录制 - 那么请不要忘记将setCategory更改为AVAudioSessionCategoryPlayAndRecord。 在其他情况下，您将无法录制

[[AVAudioSession sharedInstance] setCategory: AVAudioSessionCategoryPlayAndRecord error:&setCategoryErr];