Play audio from AVAudioPCMBuffer with AVAudioEngine - ios

Question

I have two classes, MicrophoneHandler, and AudioPlayer. I have managed to use AVCaptureSession to tap microphone data using the approved answer here, and and converted the 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)
}
I would now like to play the audio over the speaker by converting the NSData produced above to AVAudioPCMBuffer and play it using AVAudioEngine. My AudioPlayerclass 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 snippet above.
I am able to print(newBuffer), and see the memory locations of the converted buffers, but nothing comes out of the speakers. I can only imagine something is not consistent between the conversions to and from NSData. Any ideas? Thanks in advance.

Answer 1

Skip the raw NSData format
Why not use AVAudioPlayer all the way? If you positively need NSData, you can always load such data from the soundURL below. In this example, the disk buffer is something like:
let soundURL = documentDirectory.URLByAppendingPathComponent("sound.m4a")
It makes sense to record directly to a file anyway for optimal memory and resource management. You get NSData from your recording this way:
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 {}
}
Setup
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))]
Download Xcode Project:
You can find this very example here. Download the full project, which records and plays on both simulator and device, from Swift Recipes.