AVAudioRecorder averagePowerForChannel始终返回-120.0

Question

我正在尝试使用AVAudioRecorder的averagePowerForChannel方法来监控iPad/iPhone应用程序的麦克风输入电平.我有一个回调轮询循环中的平均水平 - 在iPhone上它工作正常并返回合理的水平,但由于某种原因在iPad上它总是返回-120.0.

这是我的一些设置代码:

- (void) setupMic {
if (micInput) {
    [micInput release];
    micInput = nil;
}
NSURL *newURL = [[NSURL alloc] initFileURLWithPath:@"/dev/null"];

NSMutableDictionary *recordSettings = [[NSMutableDictionary alloc] init];

[recordSettings setObject:[NSNumber numberWithInt:kAudioFormatAppleLossless] forKey: AVFormatIDKey];
[recordSettings setObject:[NSNumber numberWithFloat:22050.0] forKey: AVSampleRateKey];
//  [recordSettings setObject:[NSNumber numberWithInt:2] forKey:AVNumberOfChannelsKey];
[recordSettings setObject:[NSNumber numberWithInt:12800] forKey:AVEncoderBitRateKey];
[recordSettings setObject:[NSNumber numberWithInt:16] forKey:AVLinearPCMBitDepthKey];
[recordSettings setObject:[NSNumber numberWithInt: AVAudioQualityLow] forKey: AVEncoderAudioQualityKey];

micInput = [[AVAudioRecorder alloc] initWithURL:newURL settings:recordSettings error:nil];
//  [micInput setMeteringEnabled:YES];

[newURL release];
[recordSettings removeAllObjects];
[recordSettings release];
}

以及我的开始录制方法:

- (void) startRecording {
NSLog(@"startRecording!");
[micInput pause];
[micInput prepareToRecord];
micInput.meteringEnabled = YES;
[micInput record];
[micInput updateMeters];
levelTimer = [[NSTimer alloc] initWithFireDate:[NSDate dateWithTimeIntervalSinceNow:0.0] interval:0.03 target:self selector:@selector(levelTimerCallback:) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:levelTimer forMode:NSDefaultRunLoopMode];
}

以及一些levelTimer回调:

- (void)levelTimerCallback:(NSTimer *)timer {
[micInput updateMeters];
double avgPowerForChannel = pow(10, (0.05 * [micInput averagePowerForChannel:0]));
[micSprite receiveInput:avgPowerForChannel];

NSLog(@"Avg. Power: %f", [micInput averagePowerForChannel:0]);

 ...

}

在iPhone上,NSLog语句将返回合理的值,iPad将始终返回-120.0.

注意:我在cocos2d应用程序中使用它.出于某种原因,如果我重新启动iPad上的当前场景,麦克风级别将返回正确的值.

有人有什么建议吗？我在这里真的很茫然.谢谢!

Answer 1

我遇到过同样的问题.我发现将类别设置为AVAudioSessionCategoryPlayAndRecord修复它:

NSError *error;
[[AVAudioSession sharedInstance] 
    setCategory:AVAudioSessionCategoryPlayAndRecord error:&error];

if (error) {
    NSLog(@"Error setting category: %@", [error description]);
}