op-queue.swift

let operationQueue = OperationQueue()
operationQueue.maxConcurrentOperationCount = 1

while (sample != nil) {
    if let newSample = sample {
        let cgImage = self.cgImageFromSampleBuffer(newSample)!
        
        operationQueue.addOperation { // Problematic son of a
            CGImageDestinationAddImage(destination, cgImage, frameProperties as CFDictionary)
        }
    }

    sample = readerOutput.copyNextSampleBuffer()
}