Question

您好我想设置AV捕获会话以使用iphone相机捕获具有特定分辨率（如果可能，具有特定质量）的图像。这是setupping AV会话代码

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

    // Create the session
    self.captureSession = [[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.
    captureSession.sessionPreset = AVCaptureSessionPresetMedium;

    // Find a suitable AVCaptureDevice
    NSArray *cameras=[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    AVCaptureDevice *device;
    if ([UserDefaults camera]==UIImagePickerControllerCameraDeviceFront)
    {
        device =[cameras objectAtIndex:1];
    }
    else
    {
        device = [cameras objectAtIndex:0];
    };

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

    // Create a VideoDataOutput and add it to the session
    AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];
    [captureSession addOutput:output];
    NSLog(@"connections: %@", output.connections);

    // 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];


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


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

和setSession：

-(void)setSession:(AVCaptureSession *)session
{
    NSLog(@"setting session...");
    self.captureSession=session;
    NSLog(@"setting camera view");
    self.previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:session];
    //UIView *aView = self.view;
    CGRect videoRect = CGRectMake(20.0, 20.0, 280.0, 255.0);
    previewLayer.frame = videoRect; // Assume you want the preview layer to fill the view.
    [previewLayer setBackgroundColor:[[UIColor grayColor] CGColor]];
    [self.view.layer addSublayer:previewLayer];
    //[aView.layer addSublayer:previewLayer];
}

和输出方法：

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

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

    //< Add your code here that uses the image >
}

// 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
    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];

    // Release the Quartz image
    CGImageRelease(quartzImage);

    return (image);
}

一切都很标准。但是我应该在哪里以及应该更改什么来指定捕获图像的分辨率及其质量。请帮帮我

Answer 1

请参阅Apple's guide捕捉静止图像部分，了解设置一个或另一个预设时可获得的尺寸。

您应更改的参数为captureSession.sessionPreset

Answer 2

尝试使用这样的东西，其中cx和cy是你的自定义分辨率：

NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                              AVVideoScalingModeResizeAspectFill,AVVideoScalingModeKey,
                           AVVideoCodecH264, AVVideoCodecKey,
                           [NSNumber numberWithInt:cx], AVVideoWidthKey,
                           [NSNumber numberWithInt:cx], AVVideoHeightKey,
                           nil];
_videoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoSettings];

AVCaptureSession指定捕获图像的分辨率和质量obj-c iphone app

2 个答案: