AVCaptureMovieFileOutput minFreeDiskSpaceLimit not working

Question

I am trying to prevent AVCaptureSession from adding an AVCaptureMovieFileOutput when there is not enough disk space left. I'm using the following code inside viewDidload for testing:

let session = AVCaptureSession()
session.sessionPreset = AVCaptureSessionPresetHigh

let movieFileOutput = AVCaptureMovieFileOutput()
movieFileOutput.minFreeDiskSpaceLimit = 1024 * 1024 * 100 // 100 MB
movieFileOutput.maxRecordedDuration = CMTimeMakeWithSeconds(45, Int32(NSEC_PER_SEC)) // 45 sec

if (session.canAddOutput(movieFileOutput)) {
    print("Output added")
    session.addOutput(movieFileOutput)
} else {
    print("Not enough disk space??")
}

But somehow the function 'canAddOutput' always returns true. I'm testing it on a real device and only have 69.4 MB space left. Why is it not returning false?

Answer 1

From the AVCaptureOutput header file, on minFreeDiskSpaceLimit:

Specifies the minimum amount of free space, in bytes, required for recording to continue on a given volume.

The error is reported via the captureOutput:didFinishRecordingToOutputFileAtURL:fromConnections:error: delegate method.

So the fact that minFreeDiskSpaceLimit defines a condition for continued recording and the error is reported via a finish delegate method suggests to me that you must first start the capture session to use it.