小编Ste*_*ten的帖子

我正在屏幕区域进行一些运动检测.在开始检测之前,我想设置焦距和曝光并锁定它们,这样它们就不会触发假动作.因此,我将AVCaptureFocusModeAutoFocus和AVCaptureExposureModeAutoExpose发送到设备并添加KeyvalueObserver.当观察者说它已完成聚焦并改变曝光时,它会锁定它们(并开始运动检测).一切都可以正常工作,但锁定曝光会在几秒钟内崩溃应用程序",尽管在两种情况下都有相同的代码.

static void * const MyAdjustingFocusObservationContext = (void*)&MyAdjustingFocusObservationContext;
static void * const MyAdjustingExposureObservationContext = (void*)&MyAdjustingExposureObservationContext;

-(void)focusAtPoint{

   CGPoint point;
   if(fromRight) point.x = 450.0/480.0;
   else point.x = 30.0/480.0;
   point.y = 245.0/320.0;

   AVCaptureDevice *device =[AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

   if(device != nil) {
       NSError *error;
       if([device lockForConfiguration:&error]){

          if([device isExposureModeSupported:AVCaptureFocusModeContinuousAutoFocus] && [device isFocusPointOfInterestSupported]) {
             [device setFocusPointOfInterest:point];
             [device setFocusMode:AVCaptureFocusModeContinuousAutoFocus];
             [device addObserver:self forKeyPath:@"adjustingFocus" options:NSKeyValueObservingOptionNew context:MyAdjustingFocusObservationContext];
             NSLog(@"focus now");
          }

          if([device isExposureModeSupported:AVCaptureExposureModeContinuousAutoExposure] && [device isExposurePointOfInterestSupported]) {
             [device setExposurePointOfInterest:point];
             [device setExposureMode:AVCaptureExposureModeContinuousAutoExposure];
             [device addObserver:self forKeyPath:@"adjustingExposure" options:NSKeyValueObservingOptionNew context:MyAdjustingExposureObservationContext];
             NSLog(@"expose now");
          }

          [device unlockForConfiguration];
      }else{ …

我正在使用AVAssetWriter来保存来自摄像头的实时信息.这很适合使用此代码

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

 CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
 CMTime lastSampleTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);

 if(videoWriter.status != AVAssetWriterStatusWriting){
    [videoWriter startWriting];
    [videoWriter startSessionAtSourceTime:lastSampleTime];
 }

 if(adaptor.assetWriterInput.readyForMoreMediaData) [adaptor appendPixelBuffer:imageBuffer withPresentationTime:lastSampleTime];
 else NSLog(@"adaptor not ready",);
}

我通常接近30 fps(但是其他人注意到iPhone 4s上的速度不是60 fps),而当定时[适配器appendPixelBuffer]它只需要几毫秒.

但是,我不需要全帧,但我需要高质量(低压缩,每帧关键帧),我将在几次后读回一个过程.因此,我想在写作之前裁剪图像.幸运的是我只需要一个中间的条带,所以我可以做一个简单的缓冲区memcpy.为此,我创建了一个CVPixelBufferRef,我正在使用适配器进行复制和写入:

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

 CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
 CMTime lastSampleTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);

 if(videoWriter.status != AVAssetWriterStatusWriting){
    [videoWriter startWriting];
    [videoWriter startSessionAtSourceTime:lastSampleTime];
 }

 CVPixelBufferLockBaseAddress(imageBuffer,0);
 size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
 size_t width = CVPixelBufferGetWidth(imageBuffer);
 size_t height = CVPixelBufferGetHeight(imageBuffer);
 void * buffIn = CVPixelBufferGetBaseAddress(imageBuffer);

 CVPixelBufferRef pxbuffer = …