AVFoundation自定义录像机音频问题

Question

我试图学习如何创建自定义录像机，一切工作良好，除了音频有很多嘈杂的声音。我在系统相机、instagram或任何其他相机应用程序中尝试，它们的音频质量非常好，没有某种低音。此外，视频的录制量也明显低于其他相机应用。我在stackoverflow上找不到任何答案，其中大多数有关于AvAudioSession的答案，但在AvCapturesession上没有。

_session =  [[AVCaptureSession alloc]init];

NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeAudio];
AVCaptureDeviceInput *audioInput = [[AVCaptureDeviceInput alloc] initWithDevice:[devices objectAtIndex:0] error:nil];
if ([_session canAddInput:audioInput])
    [_session addInput:audioInput];

AVCaptureDevice *inputDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
AVCaptureDeviceInput *deviceInput = [AVCaptureDeviceInput deviceInputWithDevice:inputDevice error:nil];
if ( [_session canAddInput:deviceInput] )
    [_session addInput:deviceInput];

_videoOutput = [[AVCaptureVideoDataOutput alloc] init];
_videoOutput.alwaysDiscardsLateVideoFrames = NO;

if ( [_session canAddOutput:_videoOutput] )
    [_session addOutput:_videoOutput];

_audioOutput = [[AVCaptureAudioDataOutput alloc] init];

if ( [_session canAddOutput:_audioOutput] )
    [_session addOutput:_audioOutput];

AVCaptureVideoPreviewLayer *previewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:_session];
[previewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];

CALayer *rootLayer = [[self view] layer];
[rootLayer setMasksToBounds:YES];
[previewLayer setFrame:CGRectMake(0, 0, rootLayer.bounds.size.width, rootLayer.bounds.size.height)];
[rootLayer insertSublayer:previewLayer atIndex:0];

[_session setSessionPreset:AVCaptureSessionPresetHigh];

dispatch_queue_t queue = dispatch_queue_create("MyQueue", NULL);
[_videoOutput setSampleBufferDelegate:self queue:queue];
[_audioOutput setSampleBufferDelegate:self queue:queue];


AVCaptureConnection *videoConnection = [_videoOutput connectionWithMediaType:AVMediaTypeVideo];
[videoConnection setVideoOrientation:AVCaptureVideoOrientationPortrait];

[_session startRunning];

1. 如何提高录制视频时的音频质量？
2. 如何增加视频的录制量？

我知道如何增加它时，只是纯录制音频与下面的代码，但不是当录制视频。

 [[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayAndRecord withOptions:(AVAudioSessionCategoryOptionDefaultToSpeaker | AVAudioSessionCategoryOptionAllowBluetooth) error:&sessionCategoryError];

Answer 1

好吧，我终于想通了。创建AvCaptureSession后，执行以下代码。

 AVAudioSession *audioSession = [AVAudioSession sharedInstance];
[audioSession setCategory:AVAudioSessionCategoryPlayAndRecord withOptions:(AVAudioSessionCategoryOptionDefaultToSpeaker | AVAudioSessionCategoryOptionAllowBluetooth) error:nil];
[audioSession setActive:YES error:nil];

_session =  [[AVCaptureSession alloc]init];

//the 2 line below is very important. 
_session.usesApplicationAudioSession = YES;
_session.automaticallyConfiguresApplicationAudioSession = NO;

现在视频的输出音频甚至比系统更好