AVFoundation，如何在捕捉 StillImageAsynouslyFromConnection 时关闭快门声音？

The only possible work-around I can think of would be to mute the iphone sound when they press the "take picture" button, and then un-mute it a second later.

Method 1: Not sure if this will work, but try playing a blank audio file right before you send the capture event.

To play a clip, add the Audio Toolbox framework, #include <AudioToolbox/AudioToolbox.h> and play the audio file like this immediately before you take the picture:

 NSString *path = [[NSBundle mainBundle] pathForResource:@"blank" ofType:@"wav"];
SystemSoundID soundID;
NSURL *filePath = [NSURL fileURLWithPath:path isDirectory:NO];
AudioServicesCreateSystemSoundID((CFURLRef)filePath, &soundID);
AudioServicesPlaySystemSound(soundID);

Here is a blank audio file if you need it. https://d1sz9tkli0lfjq.cloudfront.net/items/0Y3Z0A1j1H2r1c0z3n3t/blank.wav

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Method 2: There's also an alternative if this doesn't work. As long as you don't need to have a good resolution, you can grab a frame from the video stream, thus avoiding the picture sound altogether.

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Method 3: Another way to do this would be to take a "screenshot" of your application. Do it this way:

UIGraphicsBeginImageContext(self.window.bounds.size);
[self.window.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
NSData * data = UIImagePNGRepresentation(image);
[data writeToFile:@"foo.png" atomically:YES];

If you're wanting this to fill the whole screen with a preview of the video stream so that your screenshot looks good:

AVCaptureSession *captureSession = yourcapturesession;
AVCaptureVideoPreviewLayer *previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:captureSession];
UIView *aView = theViewYouWantTheLayerIn;
previewLayer.frame = aView.bounds; // Assume you want the preview layer to fill the view.
[aView.layer addSublayer:previewLayer];

A common trick in such cases is to find out if the framework invokes a certain method for this event, and then to overwrite that method temporarily, thereby voiding its effect.

I'm sorry but I am not a good enough hack to tell you right away if that works in this case. You could try the "nm" command on the framework executables to see if there's a named function that has a suitatable name, or use gdb with the Simulator to trace where it goes.

Once you know what to overwrite, there are those low level ObjC dispatching functions that you can use to redirect the lookup for functions, I believe. I think I've done that once a while ago, but can't remember the details.

Hopefully, you can use my hints to google a few solutions paths to this. Good luck.

I live in in Japan, so I can not mute the audio when we take photos for security reason. In video, however audio turns off. I don't understand why.

The only way I take a photo without shutter sound is using AVCaptureVideoDataOutput or AVCaptureMovieFileOutput. For analyze still image AVCaptureVideoDataOutput is only way. In AVFoundatation sample code,

AVCaptureVideoDataOutput *output = [[[AVCaptureVideoDataOutput alloc] init] autorelease];
// If you wish to cap the frame rate to a known value, such as 15 fps, set
// minFrameDuration.
output.minFrameDuration = CMTimeMake(1, 15);

In my 3GS it is very heavy when I set CMTimeMake(1, 1); // One frame per second.

In WWDC 2010 Sample code, FindMyiCone, I found following code,

[output setAlwaysDiscardsLateVideoFrames:YES];

When this API is used, the timing is not granted, but API is called sequentially. I this it is best solutions.

I used this code once to capture iOS default shutter sound (here is list of sound file names https://github.com/TUNER88/iOSSystemSoundsLibrary):

NSString *path = @"/System/Library/Audio/UISounds/photoShutter.caf";
NSString *docs = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
NSData *data = [NSData dataWithContentsOfFile:path];
[data writeToFile:[docs stringByAppendingPathComponent:@"photoShutter.caf"] atomically:YES];

Then I used third-party app to extract photoShutter.caf from Documents directory (DiskAid for Mac). Next step I opened photoShutter.caf in Audacity audio editor and applied inversion effect, it looks like this on high zoom:

Then I saved this sound as photoShutter2.caf and tried to play this sound right before captureStillImageAsynchronouslyFromConnection:

static SystemSoundID soundID = 0;
if (soundID == 0) {
NSString *path = [[NSBundle mainBundle] pathForResource:@"photoShutter2" ofType:@"caf"];
NSURL *filePath = [NSURL fileURLWithPath:path isDirectory:NO];
AudioServicesCreateSystemSoundID((__bridge CFURLRef)filePath, &soundID);
}
AudioServicesPlaySystemSound(soundID);


[self.stillImageOutput captureStillImageAsynchronouslyFromConnection:
...

And this really works! I runs test several times, every time I hear no shutter sound :)

You can get already inverted sound, captured on iPhone 5S iOS 7.1.1 from this link: https://www.dropbox.com/s/1echsi6ivbb85bv/photoShutter2.caf

You can also take a frame from a video stream to capture a (not full resolution) image.

It is used here to capture images at short intervals:

- (IBAction)startStopPictureSequence:(id)sender
{
if (!_capturingSequence)
{
if (!_captureVideoDataOutput)
{
_captureVideoDataOutput = [AVCaptureVideoDataOutput new];
_captureVideoDataOutput.videoSettings = @{(NSString *)kCVPixelBufferPixelFormatTypeKey: @(kCVPixelFormatType_32BGRA)};
[_captureVideoDataOutput setSampleBufferDelegate:self
queue:dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0)];
if (_sequenceCaptureInterval == 0)
{
_sequenceCaptureInterval = 0.25;
}
}


if ([_captureSession canAddOutput:_captureVideoDataOutput])
{
[_captureSession addOutput:_captureVideoDataOutput];
_lastSequenceCaptureDate = [NSDate date]; // Skip the first image which looks to dark for some reason
_sequenceCaptureOrientation = (_currentDevice.position == AVCaptureDevicePositionFront ? // Set the output orientation only once per sequence
UIImageOrientationLeftMirrored :
UIImageOrientationRight);
_capturingSequence = YES;
}
else
{
NBULogError(@"Can't capture picture sequences here!");
return;
}
}
else
{
[_captureSession removeOutput:_captureVideoDataOutput];
_capturingSequence = NO;
}
}


- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
fromConnection:(AVCaptureConnection *)connection
{
// Skip capture?
if ([[NSDate date] timeIntervalSinceDate:_lastSequenceCaptureDate] < _sequenceCaptureInterval)
return;


_lastSequenceCaptureDate = [NSDate date];


UIImage * image = [self imageFromSampleBuffer:sampleBuffer];
NBULogInfo(@"Captured image: %@ of size: %@ orientation: %@",
image, NSStringFromCGSize(image.size), @(image.imageOrientation));


// Execute capture block
dispatch_async(dispatch_get_main_queue(), ^
{
if (_captureResultBlock) _captureResultBlock(image, nil);
});
}


- (BOOL)isRecording
{
return _captureMovieOutput.recording;
}

See this post for a different kind of answer: Capture the image from the image buffer. Screen capture during video preview fails

I was able to get this to work by using this code in the snapStillImage function and it works perfectly for me on iOS 8.3 iPhone 5. I have also confirmed that Apple won't reject your app if you use this (they didn't reject mine)

MPVolumeView* volumeView = [[MPVolumeView alloc] init];
//find the volumeSlider
UISlider* volumeViewSlider = nil;
for (UIView *view in [volumeView subviews]){
if ([view.class.description isEqualToString:@"MPVolumeSlider"]){
volumeViewSlider = (UISlider*)view;
break;
}
}
// mute it here:
[volumeViewSlider setValue:0.0f animated:YES];
[volumeViewSlider sendActionsForControlEvents:UIControlEventTouchUpInside];

Just remember to be nice and unmute it when your app returns!

My Solution in Swift

When you call AVCapturePhotoOutput.capturePhoto method to capture an image like the below code.

photoOutput.capturePhoto(with: self.capturePhotoSettings, delegate: self)

AVCapturePhotoCaptureDelegate methods will be invoked. And the system tries to play shutter sound after willCapturePhotoFor invoked. So you can dispose of system sound in willCapturePhotoFor method.

extension PhotoCaptureService: AVCapturePhotoCaptureDelegate {


func photoOutput(_ output: AVCapturePhotoOutput, willCapturePhotoFor resolvedSettings: AVCaptureResolvedPhotoSettings) {
// dispose system shutter sound
AudioServicesDisposeSystemSoundID(1108)
}
}

See also

• AVCapturePhotoDelegate