thank you for that @ssmith_c ! i realised that I didn't have that structure protocol setup that way. I now can record frames properly with queueDepth = 8. However, there is another issue I run into (which I don't know how to reproduce or trigger it) My stream suddenly breaks/stops sometimes and I get the error: EXC_BAD_ACCESS (code=1, address=0x0) I catch it in this function: func stream(_ stream: SCStream, didStopWithError error: Error) { print("Stream stopped with error: \(error.localizedDescription)") if isRecording { isRecording = false if let session = compressionSession { VTCompressionSessionCompleteFrames(session, untilPresentationTimeStamp: .positiveInfinity) VTCompressionSessionInvalidate(session) } compressionSession = nil self.stream = nil self.bufferQueue.async { print("[DEBUG] Buffer size before restart: \(self.circularBuffer.count)") } // Attempt to restart self.start() self.bufferQueue.async { print("[DEBUG] Buffer size after restart: \(self.circularBuffer.count)") } } } one moment, the stream would be running properly and then the next, it stops. What are generally the steps to debug in this scenario? I added exception breakpoints but I don't exactly know what to look for and where to look for. I added zombie objects detection as well but I don't know what to check for..