Playing WAV data with AVAudioEngine - objective-c

Question

Currently, I'm getting an EXC_BAD_ACCESS error on the audio thread, and I'm trying to deduce what is going wrong.
When converting .wav file data from Data to an AVAudioPCMBuffer, do I need to strip the RIFF header first?
import AVFoundation
public class Player : NSObject {
let engine = AVAudioEngine()
public override init() {
super.init()
do {
let _ = engine.mainMixerNode
try engine.start()
} catch {
print("Player error: \(error)")
}
}
#objc public func play(_ data: Data) {
let format = AVAudioFormat(commonFormat: .pcmFormatInt16, sampleRate: 48000, channels: 2, interleaved: true)!
let buffer = data.toPCMBuffer(format: format)!
let player = AVAudioPlayerNode()
engine.attach(player)
engine.connect(player, to: engine.mainMixerNode, format: nil)
player.scheduleBuffer(buffer, at: nil, completionCallbackType: .dataPlayedBack) {
callbackType in
// Nothing in here.
}
player.play()
}
}
Here's the toPCMBuffer extension:
// Taken from: https://stackoverflow.com/a/52731480/2228559
extension Data {
func toPCMBuffer(format: AVAudioFormat) -> AVAudioPCMBuffer? {
let streamDesc = format.streamDescription.pointee
let frameCapacity = UInt32(count) / streamDesc.mBytesPerFrame
guard let buffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: frameCapacity) else { return nil }
buffer.frameLength = buffer.frameCapacity
let audioBuffer = buffer.audioBufferList.pointee.mBuffers
withUnsafeBytes { addr in
audioBuffer.mData?.copyMemory(from: addr, byteCount: Int(audioBuffer.mDataByteSize))
}
return buffer
}
}
Note: I cannot use AVAudioFile because the .wav file data is loaded over-the-wire.

Answer 1

IDK, but my mac crashes if I play interleaved AVAudioPCMBuffers, and garbled audio if they're not float data, so you could convert to non-interleaved float data:
#objc public func play(_ data: Data) {
let sampleRate: Double = 48000
let interleavedFormat = AVAudioFormat(commonFormat: .pcmFormatInt16, sampleRate: sampleRate, channels: 2, interleaved: true)!
let interleavedBuffer = data.toPCMBuffer(format: interleavedFormat)!
let nonInterleavedFormat = AVAudioFormat(commonFormat: .pcmFormatFloat32, sampleRate: sampleRate, channels: 2, interleaved: false)!
let nonInterleavedBuffer = AVAudioPCMBuffer(pcmFormat: nonInterleavedFormat, frameCapacity: interleavedBuffer.frameCapacity)!
nonInterleavedBuffer.frameLength = interleavedBuffer.frameLength
let converter = AVAudioConverter(from: interleavedFormat, to: nonInterleavedFormat)!
try! converter.convert(to: nonInterleavedBuffer, from: interleavedBuffer)
let player = AVAudioPlayerNode()
engine.attach(player)
engine.connect(player, to: engine.mainMixerNode, format: nil)
player.scheduleBuffer(nonInterleavedBuffer, at: nil, completionCallbackType: .dataPlayedBack) {
callbackType in
// Nothing in here.
}
player.play()
}
extension Data {
func toPCMBuffer(format: AVAudioFormat) -> AVAudioPCMBuffer? {
assert(format.isInterleaved)
let streamDesc = format.streamDescription.pointee
let frameCapacity = UInt32(count) / streamDesc.mBytesPerFrame
guard let buffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: frameCapacity) else { return nil }
buffer.frameLength = buffer.frameCapacity
let b = UnsafeMutableBufferPointer(start: buffer.int16ChannelData![0], count: buffer.stride * Int(frameCapacity))
let bytesCopied = self.copyBytes(to: b)
assert(bytesCopied == count)
return buffer
}
}