问题
I'm trying to play a pure sine wave tone using Core Audio AudioQueue's (Swift 3).
It plays nicely, but I'm getting popping noises every time my AudioQueueOutputCallback is invoked to fill a new buffer with audio data.
My AudioStreamer class looks like:
let kNumberBuffers = 3
protocol AudioStreamerDelegate {
func requestAudioData() -> [Float]
}
let sampleRate = 48000.0
let bufferSize = Int(sampleRate) / 50
let bufferByteSize = UInt32(bufferSize * sizeof(Float)) // 20 mili sec of audio
class AudioStreamer {
var delegate: AudioStreamerDelegate
var outputQueue: AudioQueueRef?
var buffers = [AudioQueueBufferRef?](repeatElement(nil, count: kNumberBuffers))
var streamBasicDescription = AudioStreamBasicDescription(
mSampleRate: sampleRate,
mFormatID: kAudioFormatLinearPCM,
mFormatFlags: kAudioFormatFlagsNativeFloatPacked | kAudioFormatFlagIsNonInterleaved,
mBytesPerPacket: UInt32(sizeof(Float)),
mFramesPerPacket: 1,
mBytesPerFrame: UInt32(sizeof(Float)),
mChannelsPerFrame: 1,
mBitsPerChannel: UInt32(8 * sizeof(Float)),
mReserved: 0
)
init(delegate: AudioStreamerDelegate) {
// create new output audio queue
self.delegate = delegate
}
func play() {
let queue = DispatchQueue.main
queue.async(execute: {
let selfPointer = unsafeBitCast(self, to: UnsafeMutablePointer<Void>.self)
AudioQueueNewOutput(
&self.streamBasicDescription,
AudioStreamerOuputCallback,
selfPointer,
nil,
nil,
0,
&self.outputQueue
)
// allocate buffers
for i in 0 ..< kNumberBuffers {
AudioQueueAllocateBuffer(
self.outputQueue!,
bufferByteSize,
&self.buffers[i]
)
if let bufferRef = self.buffers[i] {
// configure audio buffer
let selfPointer = unsafeBitCast(self, to: UnsafeMutablePointer<Void>.self)
bufferRef.pointee.mUserData = selfPointer
bufferRef.pointee.mAudioDataByteSize = bufferByteSize
}
}
AudioQueuePrime(self.outputQueue!, 0, nil)
for bufferRef in self.buffers {
AudioStreamerOuputCallback(userData: unsafeBitCast(self, to: UnsafeMutablePointer<Void>.self), queueRef: self.outputQueue!, buffer: bufferRef!)
}
AudioQueueStart(self.outputQueue!, nil)
})
}
}
func AudioStreamerOuputCallback(userData: Optional<UnsafeMutablePointer<Void>>, queueRef: AudioQueueRef, buffer: AudioQueueBufferRef) {
let this = Unmanaged<AudioStreamer>.fromOpaque(OpaquePointer(userData!)).takeUnretainedValue()
let audioData = this.delegate.requestAudioData()
memcpy(buffer.pointee.mAudioData, unsafeBitCast(audioData, to: UnsafeMutablePointer<Void>.self), Int(bufferByteSize))
AudioQueueEnqueueBuffer(queueRef, buffer, 0, nil)
}
Audio data generator method of a ViewController class with just a "play" button (theta is a stored property on that ViewController):
func generateAudioData(frequency: Double) {
semaphore.wait()
let amplitude: Double = 0.25
let theta_increment: Double = 2.0 * M_PI * frequency / sampleRate
for j in 0 ..< Int(bufferSize) {
audioData[j] = Float(sin(theta) * amplitude)
theta += theta_increment
if theta > 2.0 * M_PI {
theta -= 2.0 * M_PI
}
}
}
The problem looks like something similar to that on this question, but nobody answered.
Any help will be greatly appreciated.
回答1:
In your output callback, you did not generate a new set of audio data, where the phase of the new buffer's first sample is an increment of the last sample of from previous buffer.
来源:https://stackoverflow.com/questions/38509920/popping-noise-between-audioqueuebuffers