QTKit, capture video for live streaming - cocoa

Question

I am trying to create an application for the Mac that would create live video streaming. I know about VLC and other solutions, but still.
To that end i am trying to record video from iSight using QTKit, and save it continuously as a series of tiny video files. However, the recording turns out not quite continuous, with gaps between the files.
Basically, I am just setting up a timer, that starts recording to a new file at certain time intervals, thus stopping the old recording. I also tried setting the max recorded length, and using a delegate method ...didFinishRecording... and ...willFinishRecording..., but with the same result (i can't really estimate the difference between the gaps in these cases).
Please, help me, if you know how these things should be done.
Here is my current code:
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
QTCaptureSession *session = [[QTCaptureSession alloc] init];
QTCaptureDevice *iSight = [QTCaptureDevice defaultInputDeviceWithMediaType:QTMediaTypeVideo];
[iSight open:nil];
QTCaptureDeviceInput *myInput = [QTCaptureDeviceInput deviceInputWithDevice:iSight];
output = [[QTCaptureMovieFileOutput alloc] init] ; //ivar, QTCaptureFileOutput
[output setDelegate:self];
a = 0; //ivar, int
fileName = #"/Users/dtv/filerecording_"; //ivar, NSString
[session addOutput:output error:nil];
[session addInput:myInput error:nil];
[capview setCaptureSession:session]; //IBOutlet
[session startRunning];
[output setCompressionOptions:[QTCompressionOptions compressionOptionsWithIdentifier:#"QTCompressionOptionsSD480SizeH264Video"] forConnection:[[output connections] objectAtIndex:0]];
[output recordToOutputFileURL:[NSURL fileURLWithPath:[NSString stringWithFormat:#"%#%i.mov", fileName, a]] bufferDestination:QTCaptureFileOutputBufferDestinationOldFile];
NSTimer *tmr = [NSTimer timerWithTimeInterval:5 target:self selector:#selector(getMovieLength:) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:tmr forMode:NSDefaultRunLoopMode];
}
‐ (void) getMovieLength:(NSTimer *) t {
a++;
[output recordToOutputFileURL:[NSURL fileURLWithPath:[NSString stringWithFormat:#"%#%i.mov", fileName, a]] bufferDestination:QTCaptureFileOutputBufferDestinationOldFile];
}

Answer 1

There is a native mechanism to brake the captured movie into pieces. Use
[QTCaptureFileOutput setMaximumRecordedDuration:]
to specify the duration of the piece or
[QTCaptureFileOutput setMaximumRecordedFileSize:]
to specify the file size limit.
When the limit is reached the delegate method will be called:
[QTCaptureFileOutput_Delegate captureOutput: shouldChangeOutputFileAtURL: forConnections: dueToError:]
In the this method you can set the new file name:
[QTCaptureFileOutput recordToOutputFileURL:]
This will allow you to cut the pieces of the recorded movie pretty precisely.
Note, that [QTCaptureFileOutput_Delegate captureOutput: didFinishRecordingToOutputFileAtURL: forConnections: dueToError:] will be called a bit later after the recoding into the file has been actually finished. If you use this method to set the new file you will have gaps in the final video. It does not mean you do not need to use this method though. This method will indicated when the piece of the movie is ready to be used.
If you need even more precise cutting you can use
[QTCaptureFileOutput captureOutput: didOutputSampleBuffer: fromConnection:]
to specify the exact movie frame when to start recording into a new piece. However, you will need more specific knowledge to work with the method.