how to play sound with AVAudioPCMBuffer

Question

I Cannot play sound with AVAudioPCMBuffer (though I could play with AVAudioFile). I got this error.

ERROR: AVAudioBuffer.mm:169: -[AVAudioPCMBuffer initWithPCMFormat:frameCapacity:]: required condition is false: isCommonFormat

here is my code below, and I'd really appreciate for your help.

import UIKit
import AVFoundation

class ViewController: UIViewController {

let audioEngine: AVAudioEngine = AVAudioEngine()
let audioFilePlayer: AVAudioPlayerNode = AVAudioPlayerNode()

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    audioEngine.attachNode(audioFilePlayer)

    let filePath: String = NSBundle.mainBundle().pathForResource("test", ofType: "mp3")!
    let fileURL: NSURL = NSURL(fileURLWithPath: filePath)!
    let audioFile = AVAudioFile(forReading: fileURL, error: nil)
    let audioFormat = audioFile.fileFormat
    let audioFrameCount = UInt32(audioFile.length)
    let audioFileBuffer = AVAudioPCMBuffer(PCMFormat: audioFormat, frameCapacity: audioFrameCount)

    var mainMixer = audioEngine.mainMixerNode
    audioEngine.connect(audioFilePlayer, to:mainMixer, format: audioFileBuffer.format)

    audioFilePlayer.scheduleBuffer(audioFileBuffer, atTime: nil, options: nil, completionHandler: nil)

    var engineError: NSError?
    audioEngine.startAndReturnError(&engineError)

    audioFilePlayer.play()
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

}

Answer 1

just let me share, this worked somehow, though I don't understand fully.

import UIKit
import AVFoundation

class ViewController: UIViewController {

var audioEngine: AVAudioEngine = AVAudioEngine()
var audioFilePlayer: AVAudioPlayerNode = AVAudioPlayerNode()

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.


    let filePath: String = NSBundle.mainBundle().pathForResource("test", ofType: "mp3")!
    println("\(filePath)")
    let fileURL: NSURL = NSURL(fileURLWithPath: filePath)!
    let audioFile = AVAudioFile(forReading: fileURL, error: nil)
    let audioFormat = audioFile.processingFormat
    let audioFrameCount = UInt32(audioFile.length)
    let audioFileBuffer = AVAudioPCMBuffer(PCMFormat: audioFormat, frameCapacity: audioFrameCount)
    audioFile.readIntoBuffer(audioFileBuffer, error: nil)

    var mainMixer = audioEngine.mainMixerNode
    audioEngine.attachNode(audioFilePlayer)
    audioEngine.connect(audioFilePlayer, to:mainMixer, format: audioFileBuffer.format)
    audioEngine.startAndReturnError(nil)

    audioFilePlayer.play()
    audioFilePlayer.scheduleBuffer(audioFileBuffer, atTime: nil, options: nil, completionHandler: nil)
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

}

Answer 2

When using an AVAudioPCMBuffer() you'll get strange errors if you try and use a pcmFormat that's not mixer.outputFormat(forBus: 0)

It will not accept mono channel formats, it will complain about mismatches between the mixer's output format and your format even if you've described them exactly the same and it won't produce errors that explain exactly what the problem is.

Answer 3

The problem is you're setting the format of your PCM buffer to a non-PCM format. Therefore, you need to create your AVAudioPCMBuffer with the AVAudioFile's processingFormat.