如何使用AVFoundation框架设置视频输入

Question

我从另一篇stackoverflow帖子中得到了这段代码，它似乎很好地完成了我想做的事情：

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

    CFDictionaryRef metadataDict = CMCopyDictionaryOfAttachments(NULL,
                                                                 sampleBuffer, kCMAttachmentMode_ShouldPropagate);
    NSDictionary *metadata = [[NSMutableDictionary alloc]
                              initWithDictionary:(__bridge NSDictionary*)metadataDict];
    CFRelease(metadataDict);
    NSDictionary *exifMetadata = [[metadata
                                   objectForKey:(NSString *)kCGImagePropertyExifDictionary] mutableCopy];
    float brightnessValue = [[exifMetadata
                              objectForKey:(NSString *)kCGImagePropertyExifBrightnessValue] floatValue];
    NSLog(@"AVCapture: %f", brightnessValue);
}

但由于我对AVFoundation了解不多，我不知道如何使用它……如何获取AVCaptureOutput、CMSampleBufferRef和AVCaptureConnection对象？

或者换句话说，“如何使用AVFoundation框架设置视频输入”？

Answer 1

下面的代码应该可以帮助您设置具有SampleBufferDelegate的CaptureSession：

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

AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];
[session addInput:input];

AVCaptureVideoDataOutput *output = [[AVCaptureVideoDataOutput alloc] init];
[session addOutput:output];

dispatch_queue_t queue = dispatch_queue_create("VideoQueue", NULL);
[output setSampleBufferDelegate:self queue:queue];

NSDictionary *outputSettings = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA]
                                                           forKey:(id)kCVPixelBufferPixelFormatTypeKey];
[output setVideoSettings:outputSettings];

output.alwaysDiscardsLateVideoFrames = YES;

更多信息请参考：https://developer.apple.com/library/ios/documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/04_MediaCapture.html