iOS开发-实现相机app的方法［转载自官方］

This brief code example to illustrates how you can capture video and convert the frames you get to UIImage objects. It shows you how to:

• Create an AVCaptureSession object to coordinate the flow of data from an AV input device to an output
• Find the AVCaptureDevice object for the input type you want
• Create an AVCaptureDeviceInput object for the device
• Create an AVCaptureVideoDataOutput object to produce video frames
• Implement a delegate for the AVCaptureVideoDataOutput object to process video frames
• Implement a function to convert the CMSampleBuffer received by the delegate into a UIImage object

Note: To focus on the most relevant code, this example omits several aspects of a complete application, including memory management. To use AV Foundation, you are expected to have enough experience with Cocoa to be able to infer the missing pieces.

Create and Configure a Capture Session

You use an AVCaptureSession object to coordinate the flow of data from an AV input device to an output. Create a session, and configure it to produce medium resolution video frames.

AVCaptureSession *session = [[AVCaptureSession alloc] init];

session.sessionPreset = AVCaptureSessionPresetMedium;

Create and Configure the Device and Device Input

Capture devices are represented by AVCaptureDevice objects; the class provides methods to retrieve an object for the input type you want. A device has one or more ports, configured using an AVCaptureInput object. Typically, you use the capture input in its default configuration.

Find a video capture device, then create a device input with the device and add it to the session.

AVCaptureDevice *device =

        [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

NSError *error = nil;

AVCaptureDeviceInput *input =[AVCaptureDeviceInput deviceInputWithDevice:device error:&error];

if (!input) {

    // Handle the error appropriately.

}

[session addInput:input];

Create and Configure the Data Output

You use an AVCaptureVideoDataOutput object to process uncompressed frames from the video being captured. You typically configure several aspects of an output. For video, for example, you can specify the pixel format using the videoSettings property, and cap the frame rate by setting the minFrameDuration property.

Create and configure an output for video data and add it to the session; cap the frame rate to 15 fps by setting the minFrameDuration property to 1/15 second:

AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];

[session addOutput:output];

output.videoSettings =@{ (NSString *)kCVPixelBufferPixelFormatTypeKey : @(kCVPixelFormatType_32BGRA) };
output.minFrameDuration = CMTimeMake(, );

The data output object uses delegation to vend the video frames. The delegate must adopt the AVCaptureVideoDataOutputSampleBufferDelegate protocol. When you set the data output’s delegate, you must also provide a queue on which callbacks should be invoked.

dispatch_queue_t queue = dispatch_queue_create("MyQueue", NULL);

[output setSampleBufferDelegate:self queue:queue];

dispatch_release(queue);

You use the queue to modify the priority given to delivering and processing the video frames.

Implement the Sample Buffer Delegate Method

In the delegate class, implement the method (captureOutput:didOutputSampleBuffer:fromConnection:) that is called when a sample buffer is written. The video data output object delivers frames as CMSampleBuffers, so you need to convert from the CMSampleBuffer to a UIImage object. The function for this operation is shown in “Converting a CMSampleBuffer to a UIImage.”

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer  fromConnection:(AVCaptureConnection *)connection {

    UIImage *image = imageFromSampleBuffer(sampleBuffer);
    // Add your code here that uses the image.

}

Remember that the delegate method is invoked on the queue you specified in setSampleBufferDelegate:queue:; if you want to update the user interface, you must invoke any relevant code on the main thread.

Starting and Stopping Recording

After configuring the capture session, you send it a startRunning message to start the recording.

[session startRunning];

To stop recording, you send the session a stopRunning message.

DEMO Code

这个demo 运行时出了一个问题，- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer        fromConnection:(AVCaptureConnection*)connection 里载到图后把图片转换为UIImage后转出来后怎么都不显示图片， 经查后直接转为NSData传出来后一切正常， 特别说明一下。 

// 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 = AVCaptureSessionPresetLow; 

    // Find a suitable AVCaptureDevice

    AVCaptureDevice *device = [AVCaptureDevice

                               defaultDeviceWithMediaType:AVMediaTypeVideo];

    // Create a device input with the device and add it to the session.

    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device

                                                                        error:&error];

    if (!input) {

        // Handling the error appropriately.

    }

    [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];
    //ARC下不再使用
    //dispatch_release(queue);

    // Specify the pixel format

    output.videoSettings =

    [NSDictionary dictionaryWithObject:

     [NSNumber numberWithInt:kCVPixelFormatType_32BGRA]

                                forKey:(id)kCVPixelBufferPixelFormatTypeKey];

    // 添加界面显示

    AVCaptureVideoPreviewLayer *previewLayer = nil; 

    previewLayer = [[[AVCaptureVideoPreviewLayer alloc] initWithSession:session] autorelease];

    [previewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];

    CGRect layerRect = [[[self view] layer] bounds];

    [previewLayer setBounds:layerRect];

    [previewLayer setPosition:CGPointMake(CGRectGetMidX(layerRect),CGRectGetMidY(layerRect))];

[[[self view] layer] addSublayer:previewLayer];

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

    // minFrameDuration.

//    output.minFrameDuration = CMTimeMake(1, 15);

    // Start the session running to start the flow of data

    [session startRunning];

    sessionGlobal = session; 

    // Assign session to an ivar.

   //  [self setSession:session];

    isCapture = FALSE;

    UIView *v = [[UIView alloc] initWithFrame:CGRectMake(, , , )];

    v.backgroundColor = [UIColor blueColor];

    v.layer.masksToBounds = YES;

    v1 = [v retain]; 

    [self.view addSubview:v];

   // [v release];

    start = [[NSDate date] timeIntervalSince1970];

    before = start;

    num = ; 

}

 (NSTimeInterval)getTimeFromStart

{

    NSDate* dat = [NSDate dateWithTimeIntervalSinceNow:];

    NSTimeInterval now = [dat timeIntervalSince1970]*;

    NSTimeInterval b = now - start;

    return b; 

}

- (void)showImage:(NSData *)topImageData

{

    if(num > )

    {

        [sessionGlobal stopRunning]; 

        return;

    }

    num ++;

    NSString *numStr = [NSString stringWithFormat:@"%d.jpg", num];

    NSString *path = [NSHomeDirectory() stringByAppendingPathComponent:numStr];

    NSLog(@"PATH : %@", path);

    [topImageData writeToFile:path atomically:YES];

    UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(, , , )];

    imageView.layer.masksToBounds = YES;

    imageView.backgroundColor = [UIColor redColor];

    UIImage *img = [[UIImage alloc] initWithData:topImageData];

    imageView.image = img;

    [img release]; 

    [self.view addSubview:imageView];

    [imageView release];

    [self.view setNeedsDisplay]; 

//    [v1 setNeedsDisplay];

}

// Delegate routine that is called when a sample buffer was written

- (void)captureOutput:(AVCaptureOutput *)captureOutput

didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer

       fromConnection:(AVCaptureConnection *)connection

{

    NSDate* dat = [NSDate dateWithTimeIntervalSinceNow:];

    NSTimeInterval now = [dat timeIntervalSince1970]*;

    NSLog(@" before: %f  num: %f" , before, now - before);

    if((now - before) > )

    {

        before = [[NSDate date] timeIntervalSince1970];

        // Create a UIImage from the sample buffer data

        UIImage *image = [self imageFromSampleBuffer:sampleBuffer];

        if(image != nil)

        { //            NSTimeInterval t = [self getTimeFromStart];

            NSData* topImageData = UIImageJPEGRepresentation(image, 1.0);

            [self performSelectorOnMainThread:@selector(showImage:) withObject:topImageData waitUntilDone:NO];

        }

    }

}

// Create a UIImage from sample buffer data

- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer

{

    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);

    // Lock the base address of the pixel buffer

    CVPixelBufferLockBaseAddress(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();

    if (!colorSpace)

    {

        NSLog(@"CGColorSpaceCreateDeviceRGB failure");

        return nil;

    }

    // Get the base address of the pixel buffer

    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);

    // Get the data size for contiguous planes of the pixel buffer.

    size_t bufferSize = CVPixelBufferGetDataSize(imageBuffer);

    // Create a Quartz direct-access data provider that uses data we supply

    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, baseAddress, bufferSize,

                                                              NULL);

    // Create a bitmap image from data supplied by our data provider

    CGImageRef cgImage =

    CGImageCreate(width,

                  height,

                  ,

                  ,

                  bytesPerRow,

                  colorSpace,

                  kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Little,

                  provider,

                  NULL,

                  true,

                  kCGRenderingIntentDefault);

    CGDataProviderRelease(provider);

    CGColorSpaceRelease(colorSpace);

    // Create and return an image object representing the specified Quartz image

    UIImage *image = [UIImage imageWithCGImage:cgImage];

    CGImageRelease(cgImage);

    CVPixelBufferUnlockBaseAddress(imageBuffer, );

    return image;

}

7 结束捕捉 

- (void)stopVideoCapture:(id)arg

{

//停止摄像头捕抓

if(self->avCaptureSession){

[self->avCaptureSession stopRunning];

self->avCaptureSession= nil;

[labelStatesetText:@"Video capture stopped"];

}