Play audio with AVAudioPCMBuffer using AVAudioEngine

Question

I have two classes: MicrophoneHandler and AudioPlayer . I managed to use AVCaptureSession to connect microphone data using the approved answer here , and converted CMSampleBuffer to NSData using this function:

 func sendDataToDelegate(buffer: CMSampleBuffer!) { let block = CMSampleBufferGetDataBuffer(buffer) var length = 0 var data: UnsafeMutablePointer<Int8> = nil var status = CMBlockBufferGetDataPointer(block!, 0, nil, &length, &data) // TODO: check for errors let result = NSData(bytesNoCopy: data, length: length, freeWhenDone: false) self.delegate.handleBuffer(result) } 

Now I would like to play the sound above the speaker, converting the NSData created above to AVAudioPCMBuffer and play it using AVAudioEngine . My AudioPlayer class is as follows:

 var engine: AVAudioEngine! var playerNode: AVAudioPlayerNode! var mixer: AVAudioMixerNode! override init() { super.init() self.setup() self.start() } func handleBuffer(data: NSData) { let newBuffer = self.toPCMBuffer(data) print(newBuffer) self.playerNode.scheduleBuffer(newBuffer, completionHandler: nil) } func setup() { self.engine = AVAudioEngine() self.playerNode = AVAudioPlayerNode() self.engine.attachNode(self.playerNode) self.mixer = engine.mainMixerNode engine.connect(self.playerNode, to: self.mixer, format: self.mixer.outputFormatForBus(0)) } func start() { do { try self.engine.start() } catch { print("error couldn't start engine") } self.playerNode.play() } func toPCMBuffer(data: NSData) -> AVAudioPCMBuffer { let audioFormat = AVAudioFormat(commonFormat: AVAudioCommonFormat.PCMFormatFloat32, sampleRate: 8000, channels: 2, interleaved: false) // given NSData audio format let PCMBuffer = AVAudioPCMBuffer(PCMFormat: audioFormat, frameCapacity: UInt32(data.length) / audioFormat.streamDescription.memory.mBytesPerFrame) PCMBuffer.frameLength = PCMBuffer.frameCapacity let channels = UnsafeBufferPointer(start: PCMBuffer.floatChannelData, count: Int(PCMBuffer.format.channelCount)) data.getBytes(UnsafeMutablePointer<Void>(channels[0]) , length: data.length) return PCMBuffer } 

The buffer reaches the handleBuffer:buffer function when self.delegate.handleBuffer(result) is called in the first fragment above.

I can print(newBuffer) and see the memory locations of the converted buffers, but nothing comes out of the speakers. I can only imagine that there is no consistent relationship between conversions to and from NSData . Any ideas? Thanks in advance.

Answer 1

Skip raw NSData format

Why not use AVAudioPlayer fully? If you really need NSData , you can always download such data from soundURL below. In this example, the disk buffer looks something like this:

 let soundURL = documentDirectory.URLByAppendingPathComponent("sound.m4a") 

It makes sense to write directly to the file anyway for optimal memory and resource management. You get NSData from your record as follows:

 let data = NSFileManager.defaultManager().contentsAtPath(soundURL.path()) 

The code below is all you need:

Record

 if !audioRecorder.recording { let audioSession = AVAudioSession.sharedInstance() do { try audioSession.setActive(true) audioRecorder.record() } catch {} } 

Play

 if (!audioRecorder.recording){ do { try audioPlayer = AVAudioPlayer(contentsOfURL: audioRecorder.url) audioPlayer.play() } catch {} } 

Customization

 let audioSession = AVAudioSession.sharedInstance() do { try audioSession.setCategory(AVAudioSessionCategoryPlayAndRecord) try audioRecorder = AVAudioRecorder(URL: self.directoryURL()!, settings: recordSettings) audioRecorder.prepareToRecord() } catch {} 

Settings

 let recordSettings = [AVSampleRateKey : NSNumber(float: Float(44100.0)), AVFormatIDKey : NSNumber(int: Int32(kAudioFormatMPEG4AAC)), AVNumberOfChannelsKey : NSNumber(int: 1), AVEncoderAudioQualityKey : NSNumber(int: Int32(AVAudioQuality.Medium.rawValue))] 

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Download the Xcode project:

Here you can find this example here . Download the complete project, which records and plays both on the simulator and on the device, from Swift Recipes .