AVCaptureSession拍照，摄像，载图总结

AVCaptureSession

[IOS开发]拍照，摄像，载图总结

1 建立Session 

2 添加 input 

3 添加output 

4 开始捕捉

5 为用户显示当前录制状态

6 捕捉

7 结束捕捉

8 参考 

1 建立Session 

1.1 声明session 

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

// Add inputs and outputs.

[session startRunning];

1.2 设置采集的质量 

Symbol	Resolution	Comments
AVCaptureSessionPresetHigh	High	Highest recording quality. This varies per device.
AVCaptureSessionPresetMedium	Medium	Suitable for WiFi sharing. The actual values may change.
AVCaptureSessionPresetLow	Low	Suitable for 3G sharing. The actual values may change.
AVCaptureSessionPreset640x480	640x480	VGA.
AVCaptureSessionPreset1280x720	1280x720	720p HD.
AVCaptureSessionPresetPhoto	Photo	Full photo resolution. This is not supported for video output.

if ([session canSetSessionPreset:AVCaptureSessionPreset1280x720]) {

session.sessionPreset = AVCaptureSessionPreset1280x720;

}

else {

// Handle the failure.

}

1.3 重新设置session 

[session beginConfiguration];

// Remove an existing capture device.

// Add a new capture device.

// Reset the preset.

[session commitConfiguration];

2 添加input 

2.1 配置一个device (查找前后摄像头) 

NSArray *devices = [AVCaptureDevice devices];

for (AVCaptureDevice *device in devices) {

NSLog(@"Device name: %@", [device localizedName]);

if ([device hasMediaType:AVMediaTypeVideo]) {

if ([device position] == AVCaptureDevicePositionBack) {

NSLog(@"Device position : back");

}

else {

NSLog(@"Device position : front");

}

}

}

2.2 设备的前后切换 Switching Between Devices

AVCaptureSession *session = <#A capture session#>;

[session beginConfiguration];

[session removeInput:frontFacingCameraDeviceInput];

[session addInput:backFacingCameraDeviceInput];

[session commitConfiguration];

2.3 添加输入设备到当前session 

NSError *error;

AVCaptureDeviceInput *input =

[AVCaptureDeviceInput deviceInputWithDevice:device error:&error];

if (!input) {

// Handle the error appropriately.

}

AVCaptureSession *captureSession = <#Get a capture session#>;

AVCaptureDeviceInput *captureDeviceInput = <#Get a capture device input#>;

if ([captureSession canAddInput:captureDeviceInput]) {

[captureSession addInput:captureDeviceInput];

}

else {

// Handle the failure.

}

3 添加输出设备到session 

AVCaptureMovieFileOutput to output to a movie file (输出一个 视频文件)

AVCaptureVideoDataOutput if you want to process frames from the video being captured (可以采集数据从指定的视频中)

AVCaptureAudioDataOutput if you want to process the audio data being captured (采集音频)

AVCaptureStillImageOutput if you want to capture still images with accompanying metadata (采集静态图片)

3.1 添加一个output 到session 

AVCaptureSession *captureSession = <#Get a capture session#>;

AVCaptureMovieFileOutput *movieOutput = <#Create and configure a movie output#>;

if ([captureSession canAddOutput:movieOutput]) {

[captureSession addOutput:movieOutput];

}

else {

// Handle the failure.

}

3.2 保存视频到文件  Saving to a Movie File

3.2.1 声明一个输出

AVCaptureMovieFileOutput *aMovieFileOutput = [[AVCaptureMovieFileOutput alloc] init];

CMTime maxDuration = <#Create a CMTime to represent the maximum duration#>;

aMovieFileOutput.maxRecordedDuration = maxDuration;

aMovieFileOutput.minFreeDiskSpaceLimit = <#An appropriate minimum given the quality of the movie format and the duration#>;

3.2.2 配置写到指定的文件

AVCaptureMovieFileOutput *aMovieFileOutput = <#Get a movie file output#>;

NSURL *fileURL = <#A file URL that identifies the output location#>;

[aMovieFileOutput startRecordingToOutputFileURL:fileURL recordingDelegate:<#The delegate#>];

3.2.3 确定文件是否写成功

captureOutput:didFinishRecordingToOutputFileAtURL:fromConnections:error:  实现这个方法

- (void)captureOutput:(AVCaptureFileOutput *)captureOutput

didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL

fromConnections:(NSArray *)connections

error:(NSError *)error {

BOOL recordedSuccessfully = YES;

if ([error code] != noErr) {

// A problem occurred: Find out if the recording was successful.

id value = [[error userInfo] objectForKey:AVErrorRecordingSuccessfullyFinishedKey];

if (value) {

recordedSuccessfully = [value boolValue];

}

}

// Continue as appropriate...

3.3 对采集载图

3.3.1 设置采集图片的像素格式 

说实话下面这段的像素格式我也似懂非懂， 感觉是不是像素的对像素的质量会有一些影响

You can use the videoSettings property to specify a custom output format. The video settings property is a dictionary; currently, the only supported key is kCVPixelBufferPixelFormatTypeKey. The recommended pixel format choices for iPhone 4 are kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange or kCVPixelFormatType_32BGRA; for iPhone 3G the recommended pixel format choices are kCVPixelFormatType_422YpCbCr8or kCVPixelFormatType_32BGRA. Both Core Graphics and OpenGL work well with the BGRA format:

// Create a VideoDataOutput and add it to the session

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

[session addOutput:output];

// Configure your output.

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

[output setSampleBufferDelegate:self queue:queue];

dispatch_release(queue);

// Specify the pixel format

output.videoSettings =

[NSDictionary dictionaryWithObject:

[NSNumber numberWithInt:kCVPixelFormatType_32BGRA]

forKey:(id)kCVPixelBufferPixelFormatTypeKey];

3.3.2 采集静态图片

AVCaptureStillImageOutput  这个类可以采集静态图片。

Preset	iPhone 3G	iPhone 3GS	iPhone 4 (Back)	iPhone 4 (Front)
High	400x304	640x480	1280x720	640x480
Medium	400x304	480x360	480x360	480x360
Low	400x304	192x144	192x144	192x144
640x480	N/A	640x480	640x480	640x480
1280x720	N/A	N/A	1280x720	N/A
Photo	1600x1200	2048x1536	2592x1936	640x480

Pixel and Encoding Formats

Different devices support different image formats:

iPhone 3G	iPhone 3GS	iPhone 4
yuvs, 2vuy, BGRA, jpeg	420f, 420v, BGRA, jpeg	420f, 420v, BGRA, jpeg

可以自己指定想要捕捉的格式， 下面就可以指定捕捉一个JPEG的图片

AVCaptureStillImageOutput *stillImageOutput = [[AVCaptureStillImageOutput alloc] init];

NSDictionary *outputSettings = @{ AVVideoCodecKey : AVVideoCodecJPEG};

[stillImageOutput setOutputSettings:outputSettings];

如果使用JPEG图片格式， 就不应该再指定其它的压缩了， output 会自动压缩， 这个压缩会使用硬件加速。 而我们要使用这个图片数据时。 可以使用jpegStillImageNSDataRepresentation: 这个方法来获取相应的NSData，这个方法不会做重复压缩的动作。

jpegStillImageNSDataRepresentation:

Returns an NSData representation of a still image data and metadata attachments in a JPEG sample buffer.

+ (NSData *)jpegStillImageNSDataRepresentation:(CMSampleBufferRef)jpegSampleBuffer

Parameters

jpegSampleBuffer

The sample buffer carrying JPEG image data, optionally with Exif metadata sample buffer attachments.

This method throws an NSInvalidArgumentException if jpegSampleBuffer is NULL or not in the JPEG format.

Return Value

An NSData representation of jpegSampleBuffer.

Discussion

This method merges the image data and Exif metadata sample buffer attachments without re-compressing the image.

The returned NSData object is suitable for writing to disk.

捕捉图片 Capturing an Image

When you want to capture an image, you send the output a captureStillImageAsynchronouslyFromConnection:completionHandler: message. The first argument is the connection you want to use for the capture. You need to look for the connection whose input port is collecting video:

AVCaptureConnection *videoConnection = nil;

for (AVCaptureConnection *connection in stillImageOutput.connections) {

for (AVCaptureInputPort *port in [connection inputPorts]) {

if ([[port mediaType] isEqual:AVMediaTypeVideo] ) {

videoConnection = connection;

break;

}

}

if (videoConnection) { break; }

}

The second argument to captureStillImageAsynchronouslyFromConnection:completionHandler: is a block that takes two arguments: a CMSampleBuffer containing the image data, and an error. The sample buffer itself may contain metadata, such as an Exif dictionary, as an attachment. You can modify the attachments should you want, but note the optimization for JPEG images discussed in “Pixel and Encoding Formats.”

[stillImageOutput captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler:

^(CMSampleBufferRef imageSampleBuffer, NSError *error) {

CFDictionaryRef exifAttachments =

CMGetAttachment(imageSampleBuffer, kCGImagePropertyExifDictionary, NULL);

if (exifAttachments) {

// Do something with the attachments.

}

// Continue as appropriate.

}];

5 为用户显示当前的录制状态

5.1 录制预览

AVCaptureSession *captureSession = <#Get a capture session#>;

CALayer *viewLayer = <#Get a layer from the view in which you want to present the preview#>;

AVCaptureVideoPreviewLayer *captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:captureSession];

[viewLayer addSublayer:captureVideoPreviewLayer];

Video Gravity Modes

The preview layer supports three gravity modes that you set using videoGravity:

• AVLayerVideoGravityResizeAspect: This preserves the aspect ratio, leaving black bars where the video does not fill the available screen area.
• AVLayerVideoGravityResizeAspectFill: This preserves the aspect ratio, but fills the available screen area, cropping the video when necessary.
• AVLayerVideoGravityResize: This simply stretches the video to fill the available screen area, even if doing so distorts the image.

6 捕捉

下面是一个完整的过程

Putting it all Together: Capturing Video Frames as UIImage Objects

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(1, 15);

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] autorelease];

[session addOutput:output];

// Configure your output.

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

[output setSampleBufferDelegate:self queue:queue];

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(0, 0, 300, 300)];

v.backgroundColor = [UIColor blueColor];

v.layer.masksToBounds = YES;

v1 = [v retain];

[self.view addSubview:v];

// [v release];

start = [[NSDate date] timeIntervalSince1970];

before = start;

num = 0;

}

(NSTimeInterval)getTimeFromStart

{

NSDate* dat = [NSDate dateWithTimeIntervalSinceNow:0];

NSTimeInterval now = [dat timeIntervalSince1970]*1;

NSTimeInterval b = now - start;

return b;

}

- (void)showImage:(NSData *)topImageData

{

if(num > 5)

{

[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(0, 0, 100, 100)];

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:0];

NSTimeInterval now = [dat timeIntervalSince1970]*1;

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

if((now - before) > 5)

{

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,0);

// 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,

8,

32,

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, 0);

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"];

}

8 参考

xcode 自带文档 Media Capture

比较完整的捕捉代码 http://chenweihuacwh.iteye.com/blog/734229

随便找的2个

http://blog.csdn.net/guo_hongjun1611/article/details/7992294

http://blog.csdn.net/xiaobingbing/article/details/6012798