Capturing video from multiple devices simultaneously using QTKit

Question

       I have three cameras in my iMac，one is iSight(FaceTime HD Camera (Built-in)，the other two are  USB Camera。And my System version is Mac OS X 10.7.3 (11D2001)，SDKs：Mac OS X 10.7 (11E52)
       My QTKit Capture application uses multiple cameras to capture video with a frame size of 640x480 @ 30 fps simultaneously， but I've found I can only capture with one or two cameras at the same time and it is dependent on different USB port。 Is this a known limitation?

Answer 1

Fallowing is what I have done：
_captureDevices = [[NSArray alloc] initWithArray:
                       [QTCaptureDevice inputDevicesWithMediaType:QTMediaTypeVideo]];
    _captureDeviceCount = _captureDevices.count;
    NSLog(@"Find video devices :%d" ,_captureDeviceCount);
    _CaptureSessions = [[NSMutableArray alloc] initWithCapacity:_captureDeviceCount];
    _captureDeviceInputs = [[NSMutableArray alloc] initWithCapacity:_captureDeviceCount];
    _captureDecompressedVideoOutput =[[NSMutableArray alloc] initWithCapacity:_captureDeviceCount];
    _CaptureMovieFileOutputs = [[NSMutableArray alloc] initWithCapacity:_captureDeviceCount];
// Create the capture session
    for (int i = 0; i < _captureDeviceCount; i++)
        [_CaptureSessions addObject:[[QTCaptureSession alloc] init]];
        [_CaptureMovieFileOutputs addObject:[[QTCaptureMovieFileOutput alloc] init]];
         [_captureDecompressedVideoOutput addObject:[[QTCaptureDecompressedVideoOutput alloc] init]];
  for (int idex = 0; idex < _captureDeviceCount; idex++)
// Connect inputs and outputs to the session
      BOOL success = NO;
      NSError *error;
// Find a video device 
    QTCaptureDevice *tempCaptureDevice =  (QTCaptureDevice*)[_captureDevices objectAtIndex:idex];
    char tempDeviceNameUniqueID[1024] = "";
    char tempCaptureDeviceName[1024] = "";
    [[tempCaptureDevice localizedDisplayName]
     getCString:tempCaptureDeviceName maxLength:1024
     encoding:NSUTF8StringEncoding];
    [[tempCaptureDevice uniqueID]
     getCString:tempDeviceNameUniqueID maxLength:1024
     encoding:NSUTF8StringEncoding];
     NSLog(@"\nCaptureDevice: %d \nDeviceName: %s  \nUniqueID :%s\n" , idex ,tempCaptureDeviceName, tempDeviceNameUniqueID);
    success = [tempCaptureDevice open:&error];
    if (error != Nil)
        NSLog(@"CaptureDevice open:&error!");
    if (!success)
        tempCaptureDevice = nil;
        // Handle error
    if (tempCaptureDevice)
       //Add the video device to the session as a device input
                    [_captureDeviceInputs addObject:[[QTCaptureDeviceInput alloc] initWithDevice:tempCaptureDevice]];
                    success = [ [_CaptureSessions objectAtIndex:idex] addInput:[_captureDeviceInputs objectAtIndex : idex] error:&error];
        if (!success)
            // Handle error
            NSLog(@"mCaptureSession addInput error!");
// Create the movie depress output and add it to the session
        success = [ [_CaptureSessions objectAtIndex:idex] addOutput: [_captureDecompressedVideoOutput objectAtIndex:idex] error:&error];
        if (!success)
            // Handle error
            NSLog(@" Handle error");
        int _frameWidth = 640;
        int _frameHeight = 480;
        int _frameRate = 30;
        [ [_captureDecompressedVideoOutput objectAtIndex:idex]
         setMinimumVideoFrameInterval:(NSTimeInterval)1/(float)_frameRate];
        NSDictionary* captureDictionary = [NSDictionary dictionaryWithObjectsAndKeys:
                                           [NSNumber numberWithDouble:_frameWidth], (id)kCVPixelBufferWidthKey,
                                           [NSNumber numberWithDouble:_frameHeight], (id)kCVPixelBufferHeightKey,
                                           [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32ARGB, nil];
        [ [_captureDecompressedVideoOutput objectAtIndex:idex] performSelectorOnMainThread:@selector(setPixelBufferAttributes:) withObject:captureDictionary waitUntilDone:NO];
// start runing the Sessions
        [ [_CaptureSessions objectAtIndex:idex] startRunning];
}// end of   for (int idex = 0; idex < _captureDeviceCount; idex++)
Message was edited by: 08064140
Message was edited by: 08064140
Message was edited by: 08064140