Oleg Oleg - 1 year ago 87
iOS Question

ios capturing image using AVFramework

I'm capturing images using this code

#pragma mark - image capture

// Create and configure a capture session and start it running
- (void)setupCaptureSession
NSError *error = nil;

// Create the session
AVCaptureSession *session = [[AVCaptureSession alloc] init];

// Configure the session to produce lower resolution video frames, if your
// processing algorithm can cope. We'll specify medium quality for the
// chosen device.
session.sessionPreset = AVCaptureSessionPresetMedium;

// Find a suitable AVCaptureDevice
AVCaptureDevice *device = [AVCaptureDevice

// Create a device input with the device and add it to the session.
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device
if (!input)
NSLog(@"PANIC: no media input");
[session addInput:input];

// Create a VideoDataOutput and add it to the session
AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];
[session addOutput:output];

// Configure your output.
dispatch_queue_t queue = dispatch_queue_create("myQueue", NULL);
[output setSampleBufferDelegate:self queue:queue];

// Specify the pixel format
output.videoSettings =
[NSDictionary dictionaryWithObject:
[NSNumber numberWithInt:kCVPixelFormatType_32BGRA]

// If you wish to cap the frame rate to a known value, such as 15 fps, set
// minFrameDuration.

// Start the session running to start the flow of data
[session startRunning];

// Assign session to an ivar.
[self setSession:session];

// Delegate routine that is called when a sample buffer was written
- (void)captureOutput:(AVCaptureOutput *)captureOutput
fromConnection:(AVCaptureConnection *)connection
NSLog(@"captureOutput: didOutputSampleBufferFromConnection");

// Create a UIImage from the sample buffer data
UIImage *image = [self imageFromSampleBuffer:sampleBuffer];

//< Add your code here that uses the image >
[self.imageView setImage:image];
[self.view setNeedsDisplay];

// Create a UIImage from sample buffer data
- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer
NSLog(@"imageFromSampleBuffer: called");
// Get a CMSampleBuffer's Core Video image buffer for the media data
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
// Lock the base address of the pixel buffer
CVPixelBufferLockBaseAddress(imageBuffer, 0);

// Get the number of bytes per row for the pixel buffer
void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);

// Get the number of bytes per row for the pixel buffer
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
// Get the pixel buffer width and height
size_t width = CVPixelBufferGetWidth(imageBuffer);
size_t height = CVPixelBufferGetHeight(imageBuffer);

// Create a device-dependent RGB color space
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

// Create a bitmap graphics context with the sample buffer data
CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8,
bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
// Create a Quartz image from the pixel data in the bitmap graphics context
CGImageRef quartzImage = CGBitmapContextCreateImage(context);
// Unlock the pixel buffer

// Free up the context and color space

// Create an image object from the Quartz image
UIImage *image = [UIImage imageWithCGImage:quartzImage];

// Release the Quartz image

return (image);

-(void)setSession:(AVCaptureSession *)session
NSLog(@"setting session...");

Capturing code works. But!
I need to change to things:
- video stream from the camera in my view.
- getting images every (for example 5 seconds) from it.
Help me please, how can it be done?

Answer Source

Add the following line

output.minFrameDuration = CMTimeMake(5, 1);

below the comment

 // If you wish to cap the frame rate to a known value, such as 15 fps, set
 // minFrameDuration.

but above the

[session startRunning];


Use the following code to preview the camera output.

AVCaptureVideoPreviewLayer *previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:session];
UIView *aView = self.view;
CGRect videoRect = CGRectMake(0.0, 0.0, 320.0, 150.0);
previewLayer.frame = videoRect; // Assume you want the preview layer to fill the view.
[aView.layer addSublayer:previewLayer];

Edit 2: Ok fine..

Apple has provided a way to set the minFrameDuration here

So now, use the following code to set the frame duration

AVCaptureConnection *conn = [output connectionWithMediaType:AVMediaTypeVideo];

if (conn.supportsVideoMinFrameDuration)
    conn.videoMinFrameDuration = CMTimeMake(5,1);
if (conn.supportsVideoMaxFrameDuration)
    conn.videoMaxFrameDuration = CMTimeMake(5,1);