getting frames by display link

 //
  //  VideoDisplayController.m
  //  Prototype492
  //
  //  Created by Christopher Sanders on 3/7/08.
  //  Copyright 2008 __CIS492__. All rights reserved.
  //
  
  #import "VideoDisplayController.h"
  
  @implementation VideoDisplayController 
  
  /*
      start the video capture session if it's not running
  */
  - (IBAction)startVideoCapture:(id)sender
  {
  
      if(![captureSession isRunning])
      {
          [captureSession startRunning];
      }
  }
  
  /*
      stop the video capture session if it's running
  */
  
  - (IBAction)stopVideoCapture:(id)sender
  {
      if([captureSession isRunning])
      {
          [captureSession stopRunning];
      }
  
  }
  
  
  /*
  initialization of UI elements
  */
  - (void)awakeFromNib
  {
      NSLog(@"initializing video controller");
  
      if(!captureSession) {
  
          //creating capture session
  
          captureSession = [[QTCaptureSession alloc] init];
  
  
          //flags for connecting inputs and outputs
          BOOL successConnect = NO;
          NSError *error = nil;
  
  
          //finding and creating the input device and adding it to the capture session
          //if unsuccessful, send a message to error log
  
  
          //note: using QTMediaTypeMuxed for DV camera... otherwise use QTMediaTypeVideo
          videoCaptureDevice = [QTCaptureDevice defaultInputDeviceWithMediaType:QTMediaTypeMuxed];
  
          //if the video capture device is found, attempt to open it and add it to the capture session
          if(videoCaptureDevice)
          {
              successConnect = [videoCaptureDevice open:&error];
  
  
            if(!successConnect)
            {
  
                NSLog(@"error opening video capture device");
                  videoCaptureDevice = nil;
  
                //other error handling code goes here
            }
  
              captureVideoDeviceInput = [[QTCaptureDeviceInput alloc] initWithDevice:videoCaptureDevice];
  
  
              //attempt to add capture device input to the capture session
            successConnect = [captureSession addInput:captureVideoDeviceInput error:&error];
  
            if(!successConnect)
            {
                NSLog(@"error adding video capture device input to capture session");
  
                  //other error handling code goes here
              }
  
              //adding decompressed video output to capture session
  
              decompressedVideoOutput = [[QTCaptureDecompressedVideoOutput alloc] init];
  
              //assigning delegate to decompressed video output
  
              [decompressedVideoOutput setDelegate: self];
  
              successConnect = [captureSession addOutput:decompressedVideoOutput error:&error];
  
              if(!successConnect)
              {
                  NSLog(@"error adding decompressed video output to capture session");
  
                    //other error handling code goes here
  
              }
  
  
              //linking capture session to the capture view
            [captureView setCaptureSession:captureSession];
  
            //[captureSession startRunning];
          }
          else
          {
              NSLog(@"couldn't find video capture device");
          }
      }
  }
  
  
  /*
  delegate method called when decompressedVideoOutput receives a frame
  it is not called in the main thread, so a synhronized block is used
  delegates of decompressedVideoOutput receive this message 
  and then can used the provided video frame for further image processing
  
  captureOutput - the QTCaptureDecompressedVideoOutput instance that sent the frame (decompressedVideoOutput)
  videoFrame - Core Video image buffer containing the decompressed frame
  sampleBuffer sample buffer containing additional info about the frame
  connection - connnection from which vdieo was received
  */
  
  
  - (void)captureOutput:(QTCaptureOutput *)captureOutput 
          didOutputVideoFrame:(CVImageBufferRef)videoFrame
          withSampleBuffer:(QTSampleBuffer *)sampleBuffer 
          fromConnection:(QTCaptureConnection *)connection
  {
      CVImageBufferRef releasedImageBuffer;
  
  
      CVBufferRetain(videoFrame);
  
  
      @synchronized(self)
      {
          //basically, have frame to be released refer to the current frame
        //then update the reference to the current frame with the next frame in the "video stream"
          releasedImageBuffer = currentImageBuffer;
          currentImageBuffer = videoFrame;
      }
  
      CVBufferRelease(releasedImageBuffer);
  
  }
  
  
  
  
  
  /*
  event that's fired when window is closed
  stop the session and close any opened devices
  */
  - (void)windowWillClose:(NSNotification *)notification
  {
      if([captureSession isRunning])
      {
          [captureSession stopRunning];
      }
  
      if([videoCaptureDevice isOpen])
      {
          [videoCaptureDevice close];
      }
  
  }
  
  /*
  event that fires when memory is to be deallocated when object is killed
  */
  - (void)dealloc
  {
  
      [captureSession release];
      [captureVideoDeviceInput release];
      [decompressedVideoOutput release];
  
      [super dealloc];
  }
  
  
  @end
  
  
  //
  //  VideoDisplayController.h
  //  Prototype492v1.1
  //
  //  Updated by Christopher Sanders on 3/8/08.
  //  Copyright 2008 CIS492. All rights reserved.
  //
  
  #import <Cocoa/Cocoa.h>
  #import <QTKit/QTkit.h>
  #import "VideoView.h"
  
  @interface VideoDisplayController : NSOpenGLView 
  {
      QTCaptureSession *captureSession;
      QTCaptureDevice *videoCaptureDevice;
      QTCaptureDeviceInput *captureVideoDeviceInput;
      QTCaptureDecompressedVideoOutput *decompressedVideoOutput;
  
      //stores most recent frame grabbed from a CVImageBufferRef
      CVImageBufferRef currentImageBuffer;
  
  
      //this is the panel on which the video from the DV camera will be displayed
      IBOutlet QTCaptureView *captureView;
  
  
      //IBOutlet VideoView *openGLVideoView;
  
  }
  
  
  
  - (IBAction)startVideoCapture:(id)sender;
  - (IBAction)stopVideoCapture:(id)sender;
  
  
  @end