ios将摄像头捕获的视频数据转为jpeg格式

想要将摄像头进行视频录制或者拍照可以用UIImagePickerController，不过UIImagePickerController会弹出一个自己的界面，可是有时候我们不想要弹出的这个界面，那么就可以用另一种方法来获取摄像头得到的数据了。

首先需要引入一个包#import <AVFoundation/AVFoundation.h>，接下来你的类需要实现AVCaptureVideoDataOutputSampleBufferDelegate这个协议，只需要实现协议中的一个方法就可以得到摄像头捕获的数据了

- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
       fromConnection:(AVCaptureConnection *)connection
{
    // Create a UIImage from the sample buffer data
    UIImage *image = [self imageFromSampleBuffer:sampleBuffer];
    mData = UIImageJPEGRepresentation(image, 0.5);//这里的mData是NSData对象，后面的0.5代表生成的图片质量

}

下面是imageFromSampleBuffer方法，方法经过一系列转换，将CMSampleBufferRef转为UIImage对象，并返回这个对象：

// Create a UIImage from sample buffer data
- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer
{
    // 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
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);

    // Free up the context and color space
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);

    // Create an image object from the Quartz image
    //UIImage *image = [UIImage imageWithCGImage:quartzImage];
    UIImage *image = [UIImage imageWithCGImage:quartzImage scale:1.0f orientation:UIImageOrientationRight];

    // Release the Quartz image
    CGImageRelease(quartzImage);

    return (image);
}

不过要想让摄像头工作起来，还得做一些工作才行：

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

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

    // 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
                               defaultDeviceWithMediaType:AVMediaTypeVideo];//这里默认是使用后置摄像头，你可以改成前置摄像头

    // 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 dictionaryWithObjectsAndKeys:
                              [NSNumber numberWithInt:kCVPixelFormatType_32BGRA], kCVPixelBufferPixelFormatTypeKey,
                              [NSNumber numberWithInt: 320], (id)kCVPixelBufferWidthKey,
                              [NSNumber numberWithInt: 240], (id)kCVPixelBufferHeightKey,
                              nil];

    AVCaptureVideoPreviewLayer* preLayer = [AVCaptureVideoPreviewLayer layerWithSession: session];
    //preLayer = [AVCaptureVideoPreviewLayer layerWithSession:session];
    preLayer.frame = CGRectMake(0, 0, 320, 240);
    preLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
    [self.view.layer addSublayer:preLayer];
    // 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];

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

其中preLayer是一个预览摄像的界面，加不加全看自己了，位置什么的也是在preLayer.frame里可设置。这里强调一下output.videoSettings，这里可以配置输出数据的一些配置，比如宽高和视频的格式。你可以在你这个controller中的初始化调用- (void)setupCaptureSession 方法，这样摄像头就开始工作了，这里没有处理关闭什么的，大家可以查文档。

只能在真机中调试，模拟器不可以。