IOS8: Camera preview flickers when recording to a file and using AVCaptureSession/commitConfiguration

Question

Ever since IOS8, I am experiencing a strange problem when using commitConfiguration We record 5 second files via AVCaptureMovieFileOutput. When changing the files, the camera preview flickers and fades to black for a second. Also there is a stutter when stitching back the files on the receiving server.

// method that switches the output file
- (void) switchOutputFile {
    NSURL *outputUrl = [self getOutputFileUrl];
    NSLog(@"Switching to: %@", outputUrl);

    // begin configuration
    [self.captureSession beginConfiguration];

    // remove the current writer
    [self.captureSession removeOutput:self.fileOutput];

    // attach new writer
    self.fileOutput = [self attachFileWriter:self.captureSession];

    // commit configuration
    [self.captureSession commitConfiguration];

    // after this line the camera preview flickers.
    [self.fileOutput startRecordingToOutputFileURL:outputUrl recordingDelegate:self];
  } 

Answer 1

The solution is very simple - not remove and add the writer. thanks to bford from apple for the explanation! Here is the updated function method

// method that switches the output file
- (void) switchOutputFile {
    NSURL *outputUrl = [self getOutputFileUrl];
    NSLog(@"Switching to: %@", outputUrl);
    [self.fileOutput startRecordingToOutputFileURL:outputUrl recordingDelegate:self];
}