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GPUImageMovieWriter - random black frames at both ends of the recorded video

I have a recording application where the user can click the “record” button to start / stop recording. I achieve this with a baseline GPUImageVideoCamerawith the output set to GPUImageViewas well GPUImageMovieWriter.

50% of the time, the recorded clip ends with a pair (or one) of a black frame at both ends, sometimes both. The implementation is pretty simple, but it's all the same.

gpuImageView = [[GPUImageView alloc] initWithFrame:cameraView.frame];
gpuImageView.fillMode = kGPUImageFillModePreserveAspectRatioAndFill;

[cameraView addSubview:gpuImageView];

videoCamera = [[GPUImageVideoCamera alloc] initWithSessionPreset:AVCaptureSessionPresetHigh cameraPosition:(usingBackCamera) ? AVCaptureDevicePositionBack : AVCaptureDevicePositionFront];

[videoCamera addTarget:gpuImageView];
[videoCamera addTarget:movieWriter];
videoCamera.audioEncodingTarget = movieWriter;
[videoCamera startCameraCapture];

double delayToStartRecording = 0.5;
dispatch_time_t startTime = dispatch_time(DISPATCH_TIME_NOW, delayToStartRecording * NSEC_PER_SEC);
        dispatch_after(startTime, dispatch_get_main_queue(), ^(void){
            NSLog(@"Start recording");
            [movieWriter startRecording];
        });

And then stop recording as follows (while the live camera continues to display on GPUImageView.

[movieWriter finishRecording];

Has anyone else experienced this and / or found a solution to avoid black frames? I can not pause / resume camera capture to ensure smooth operation with the user.

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