我正在尝试播放来自网络的字节数组的音乐,其格式为pcmInt16数据。
// formats
let format1 = AVAudioFormat(commonFormat: AVAudioCommonFormat.pcmFormatFloat32, sampleRate: 48000, channels: 1, interleaved: false)!
let format2 = AVAudioFormat(commonFormat: AVAudioCommonFormat.pcmFormatInt16, sampleRate: 48000, channels: 1, interleaved: false)!
// byte array buffer
var byteArray: [Int16]! // one packet size is 512
...
// 1. create / attach / connect engine
engine.prepare()
try! engine.start()
engine.attach(playerNode)
engine.connect(playerNode, to: engine.mainMixerNode, format: format1)
// 2. fill byteArray with music stream // int16 48kHz 32bit
...
// 3.
var len = 512
let pcmBuffer = AVAudioPCMBuffer(pcmFormat: format2, frameCapacity: AVAudioFrameCount(len))!
// HERE
// How to set the first 512 data from byteArray ?
playerNode.scheduleBuffer(pcmBuffer, completionHandler: nil)
如何设置byteArray的前512个数据?我尝试过类似的操作,但无法正常工作:memcpy(pcmBuffer.audioBufferList.pointee.mBuffers.mData, byteArray[0..<512], len * 2)
AVAudioMixerNode非常适合sampleRate转换,但是对于从Int16到Float的宽格式更改,最好自己转换一下。为了提高性能,我建议使用vDSP Accelerate。
import Cocoa
import AVFoundation
import Accelerate
import PlaygroundSupport
let bufferSize = 512
let bufferByteSize = MemoryLayout<Float>.size * bufferSize
var pcmInt16Data: [Int16] = []
var pcmFloatData = [Float](repeating: 0.0, count: bufferSize) // allocate once and reuse
// one buffer of noise as an example
for _ in 0..<bufferSize {
let value = Int16.random(in: Int16.min...Int16.max)
pcmInt16Data.append(value)
}
let engine = AVAudioEngine()
let player = AVAudioPlayerNode()
let audioFormat = AVAudioFormat(standardFormatWithSampleRate: 48_000.0, channels: 1)!
let buffer = AVAudioPCMBuffer(pcmFormat: audioFormat, frameCapacity: UInt32(bufferSize))
let mixer = engine.mainMixerNode
engine.attach(player)
engine.connect(player, to: mixer, format: audioFormat)
engine.prepare()
do {
try engine.start()
} catch {
print("Error info: \(error)")
}
player.play()
if let buffer = AVAudioPCMBuffer(pcmFormat: audioFormat, frameCapacity: UInt32(bufferSize)) {
let monoChannel = buffer.floatChannelData![0]
// Int16 ranges from -32768 to 32767 -- we want to convert and scale these to Float values between -1.0 and 1.0
var scale = Float(Int16.max) + 1.0
vDSP_vflt16(pcmInt16Data, 1, &pcmFloatData, 1, vDSP_Length(bufferSize)) // Int16 to Float
vDSP_vsdiv(pcmFloatData, 1, &scale, &pcmFloatData, 1, vDSP_Length(bufferSize)) // divide by scale
memcpy(monoChannel, pcmFloatData, bufferByteSize)
buffer.frameLength = UInt32(bufferSize)
player.scheduleBuffer(buffer, completionHandler: nil) // load more buffers in the completionHandler
}
PlaygroundPage.current.needsIndefiniteExecution = true
[相反,如果您想播放AVAudioFile,请使用AVAudioPlayerNode.scheduleFile()和.scheduleSegment方法,而不是尝试直接从WAV / AIFF读取Int16数据。您需要注意AVAudioFile.processingFormat参数,并将其用于从播放器到混音器的连接格式。
import Cocoa
import PlaygroundSupport
import AVFoundation
let engine = AVAudioEngine()
let player = AVAudioPlayerNode()
let playEntireFile = true
func playLocalFile() {
// file needs to be in ~/Documents/Shared Playground Data
let localURL = playgroundSharedDataDirectory.appendingPathComponent("MyAwesomeMixtape6.aiff")
guard let audioFile = try? AVAudioFile(forReading: localURL) else { return }
let audioFormat = audioFile.processingFormat
let mixer = engine.mainMixerNode
engine.attach(player)
engine.connect(player, to: mixer, format: audioFormat)
engine.prepare()
do {
try engine.start()
} catch {
print("Error info: \(error)")
}
player.play()
if playEntireFile {
player.scheduleFile(audioFile, at: nil, completionHandler: nil)
} else { // play segment
let startTimeSeconds = 5.0
let durationSeconds = 2.0
let sampleRate = audioFormat.sampleRate
let startFramePostion = startTimeSeconds * sampleRate
let durationFrameCount = durationSeconds * sampleRate
player.scheduleSegment(audioFile, startingFrame: AVAudioFramePosition(startFramePostion), frameCount: AVAudioFrameCount(durationFrameCount), at: nil, completionHandler: nil)
}
}
playLocalFile()
PlaygroundPage.current.needsIndefiniteExecution = true
对于远程文件,请尝试AVPlayer。
import Cocoa
import AVFoundation
import PlaygroundSupport
var player: AVPlayer?
func playRemoteFile() {
guard let remoteURL = URL(string: "https://ondemand.npr.org/anon.npr-mp3/npr/me/2020/03/20200312_me_singapore_wins_praise_for_its_covid-19_strategy_the_us_does_not.mp3"
) else { return }
player = AVPlayer(url: remoteURL)
player?.play()
}
playRemoteFile()
PlaygroundPage.current.needsIndefiniteExecution = true
首先,最好不要尽可能使用隐式解包的可选。
var byteArray: [Int16] = [] // one packet size is 512
据显示的代码显示,无需将byteArray
设为可选。
和如何从byteArray设置第一个 512个数据?
您的代码将进行一些修改:
pcmBuffer.frameLength = AVAudioFrameCount(len)
memcpy(pcmBuffer.audioBufferList.pointee.mBuffers.mData, byteArray, len * 2)
或者您可以使用int16ChannelData
:
if let channelData = pcmBuffer.int16ChannelData {
memcpy(channelData[0], byteArray, len * MemoryLayout<Int16>.stride)
pcmBuffer.frameLength = AVAudioFrameCount(len)
} else {
print("bad format")
}
您可能想加载byteArray
的非第一部分,但这是另一个问题。