IOS adding UIProgressView to AVFoundation AVCaptureMovieFileOutput - ios

Question

I am using AVCaptureMovieFileOutput to record videos and I want to add a UIProgressView to represent how much time there is left before the video stops recording.
I set a max duration of 15 seconds:
CMTime maxDuration = CMTimeMakeWithSeconds(15, 50);
[[self movieFileOutput] setMaxRecordedDuration:maxDuration];
I can't seem to find if AVCaptureMovieFileOutput has a callback for when the video is recording or for when recording begins. My question is, how can I get updates on the progress of the recording? Or if this isn't something that is available, how can I tell when recording begins in order to start a timer?

Answer 1

Here is how I was able to add a UIProgressView
recording is a property of AVCaptureFileOutput which is extended by AVCaptureMovieFileOutput
I have a variable movieFileOutput of type AVCaptureMovieFileOutput that I am using to capture data to a QuickTime movie.
#property (nonatomic) AVCaptureMovieFileOutput *movieFileOutput;
I added an observer to the recording property to detect a change in recording.
[self addObserver:self
forKeyPath:#"movieFileOutput.recording"
options:(NSKeyValueObservingOptionOld | NSKeyValueObservingOptionNew)
context:RecordingContext];
Then in the callback method:
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context;
I created a while loop to be executed in the background, then I made sure to dispatch updates to the view on the main thread like this:
dispatch_async([self sessionQueue], ^{ // Background task started
// While the movie is recording, update the progress bar
while ([[self movieFileOutput] isRecording]) {
double duration = CMTimeGetSeconds([[self movieFileOutput] recordedDuration]);
double time = CMTimeGetSeconds([[self movieFileOutput] maxRecordedDuration]);
CGFloat progress = (CGFloat) (duration / time);
dispatch_async(dispatch_get_main_queue(), ^{ // Here I dispatch to main queue and update the progress view.
[self.progressView setProgress:progress animated:YES];
});
}
});