IOS:应用程序在后台播放声音

Question

我正在开发一个小应用程序，我想让手机从我的位置控制器上播放一个事件的声音文件。问题是，当应用程序处于后台模式时，AVAudioPlayer不会启动音频文件，但会安排代码，获取NSLog输出。另一件事是它可以在模拟器中工作，但不能在电话上工作。

为什么不呢？

这是我播放该文件的代码：

- (void)tryPlayTaleSound:(NSString*)fileName {

    NSString *backgroundMusicPath = [[NSBundle mainBundle] pathForResource:fileName ofType:@"mp3"];
    NSURL *backgroundMusicURL = [NSURL fileURLWithPath:backgroundMusicPath];
    NSError *error;

    backgroundMusicPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:backgroundMusicURL error:&error];

    // Check to see if iPod music is already playing
    //UInt32 propertySize = sizeof(otherMusicIsPlaying);
    //AudioSessionGetProperty(kAudioSessionProperty_OtherAudioIsPlaying, &propertySize, &otherMusicIsPlaying);

    // Play the music if no other music is playing and we aren't playing already
    //if (otherMusicIsPlaying != 1 && !backgroundMusicPlaying) {
    //[backgroundMusicPlayer prepareToPlay];
    [backgroundMusicPlayer play];
    backgroundMusicPlaying = YES;
    //}
    NSLog(@"%s - ", __FUNCTION__);
}

在日志中，我得到了这一点。

Apr 26 13:57:48 iPhone CommCenter[58] <Notice>: Client [com.apple.persistentconnection[dataaccessd,85]] is telling PDP context 0 to go active.
Apr 26 13:57:50 iPhone Herning100[1467] <Warning>: Playing audiofile - filename is Fil03
Apr 26 13:57:50 iPhone mediaserverd[39] <Warning>: 13:57:50.653 <AudioControl> WARNING translating CMSession error: -12985 
Apr 26 13:57:50 iPhone mediaserverd[39] <Warning>: 13:57:50.656 <AudioControl> WARNING translating CMSession error: -12985 
Apr 26 13:57:50 IPhone mediaserverd[39] <Error>: 13:57:50.734 <AudioControl> AudioQueue: Error -12985 from AudioSessionSetClientPlayState(1467)
Apr 26 13:57:50 iPhone Herning100[1467] <Warning>: -[AppDelegate tryPlayTaleSound:] - 
Apr 26 13:57:50 iPhone com.apple.debugserver-199[1465] <Warning>: 9 +28.832083 sec [05b9/0303]: error: ::mach_vm_region_recurse ( task = 0x1603, address => 0xfffffffe, size => 0, nesting_depth => 1024, info => 0x2fd7fe48, infoCnt => 12) addr = 0xfffffffe  err = (os/kern) invalid address (0x00000001)
Apr 26 13:57:51 iPhone com.apple.debugserver-199[1465] <Warning>: 10 +0.187961 sec [05b9/0303]: error: ::mach_vm_region_recurse ( task = 0x1603, address => 0xfffffffe, size => 0, nesting_depth => 1024, info => 0x2fd7fe48, infoCnt => 12) addr = 0xfffffffe  err = (os/kern) invalid address (0x00000001)

使用AVAudioPlayer和AVAudioSession有什么区别吗？

希望有人能帮上忙。

/Lasse

Answer 1

除了在Info.plist中设置后台模式audio之外，你还需要将共享音频会话设置为适合你的应用的正确模式，并在后台播放你的声音之前激活它：

AVAudioSession *audioSession = [AVAudioSession sharedInstance];
NSError *error = nil;
NSLog(@"Activating audio session");
if (![audioSession setCategory:AVAudioSessionCategoryPlayback withOptions:AVAudioSessionCategoryOptionDuckOthers error:&error]) {
    NSLog(@"Unable to set audio session category: %@", error);
}
BOOL result = [audioSession setActive:YES error:&error];
if (!result) {
    NSLog(@"Error activating audio session: %@", error);
}
[[UIApplication sharedApplication] beginReceivingRemoteControlEvents];

播放完声音后，不要忘了停用音频会话：

AVAudioSession *audioSession = [AVAudioSession sharedInstance];
NSError *error = nil;
NSLog(@"Deactivating audio session");
BOOL result = [audioSession setActive:NO error:&error];
if (!result) {
    NSLog(@"Error deactivating audio session: %@", error);
}

Answer 2

在开始在后台播放声音之前，请设置一个后台任务。如果剩余的后台时间小于10秒，iOS似乎会拒绝在后台启动声音。

Answer 3

在iOS上，只允许部分应用程序在后台运行。其中之一是音频播放器应用程序，但对于它们，你需要在你的Info.plist中设置“必要的背景模式”与“音频”(应用程序可以播放音频)。

是的，如果你能够在后台定位，那么你必须在你的Plist中设置这个关键点。在plist中也添加音频权限。