AVFoundation自定义录像机音频问题

Question

I try to learn how to create custom video recorder, everything work fine except when the audio having a lot of noisy sound. I try in the system camera, instagram or any other camera app their audio quality is very good and don't have some kind of low level sound. Beside, the recorded volume of the video also significantly lower compare to other camera app. I can't found any answer on stackoverflow which most of them having answer about AVAudioSession but not on AVCaptureSession .

Here is the code how I implement the recorder

_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];

The video quality is fine and the code working, just having trouble on the audio part. So

1. How can I improve the audio quality when recording a video?
2. How can I increase the recording volume of the video?

I know how to increase it when just pure recording an audio with the code below but not when recording video.

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

Answer 1

Ok I finally figure it out. After create the AVCaptureSession do the following code.

 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;

Now the ouput audio of the video is even better than the system