我需要从文件中提取音频表级别,以便在播放音频之前渲染级别.我知道AVAudioPlayer可以在播放音频文件时获取此信息
func averagePower(forChannel channelNumber: Int) -> Float.
但在我的情况下,我希望事先得到一个米级的[Float].
解决方法
更快的解决方案
它需要一个iPhone 6s加：
> 0.538秒处理8MByte mp3播放器,持续时间为4分47秒,采样率为44,100
> 0.170s处理712KByte MP3播放器,持续时间为22s,100
> 0.089s来处理通过在终端中使用此命令afconvert -f caff -d LEI16 audio.mp3 audio.caf转换上面的文件而创建的caffile.
让我们开始：
A)声明此类将保存有关音频资产的必要信息：
/// Holds audio information used for building waveforms
final class AudioContext {
/// The audio asset URL used to load the context
public let audioURL: URL
/// Total number of samples in loaded asset
public let totalSamples: Int
/// Loaded asset
public let asset: AVAsset
// Loaded assetTrack
public let assetTrack: AVAssetTrack
private init(audioURL: URL,totalSamples: Int,asset: AVAsset,assetTrack: AVAssetTrack) {
self.audioURL = audioURL
self.totalSamples = totalSamples
self.asset = asset
self.assetTrack = assetTrack
}
public static func load(fromAudioURL audioURL: URL,completionHandler: @escaping (_ audioContext: AudioContext?) -> ()) {
let asset = AVURLAsset(url: audioURL,options: [AVURLAssetPreferPreciseDurationAndTimingKey: NSNumber(value: true as Bool)])
guard let assetTrack = asset.tracks(withMediaType: AVMediaType.audio).first else {
fatalError("Couldn't load AVAssetTrack")
}
asset.loadValuesAsynchronously(forKeys: ["duration"]) {
var error: NSError?
let status = asset.statusOfValue(forKey: "duration",error: &error)
switch status {
case .loaded:
guard
let formatDescriptions = assetTrack.formatDescriptions as? [CMAudioFormatDescription],let audioFormatDesc = formatDescriptions.first,let asbd = CMAudioFormatDescriptionGetStreamBasicDescription(audioFormatDesc)
else { break }
let totalSamples = Int((asbd.pointee.mSampleRate) * Float64(asset.duration.value) / Float64(asset.duration.timescale))
let audioContext = AudioContext(audioURL: audioURL,totalSamples: totalSamples,asset: asset,assetTrack: assetTrack)
completionHandler(audioContext)
return
case .failed,.cancelled,.loading,.unknown:
print("Couldn't load asset: \(error?.localizedDescription ?? "Unknown error")")
}
completionHandler(nil)
}
}
}
我们将使用其异步函数load,并将其结果处理为完成处理程序.
B)在视图控制器中导入AVFoundation并加速：
import AVFoundation import Accelerate
C)在视图控制器中声明噪声级别(以dB为单位)：
let noiseFloor: Float = -80
例如,任何小于-80dB的东西都将被视为静音.
D)以下功能采用音频上下文并产生所需的dB功率. targetSamples默认设置为100,您可以更改它以满足您的UI需求：
func render(audioContext: AudioContext?,targetSamples: Int = 100) -> [Float]{
guard let audioContext = audioContext else {
fatalError("Couldn't create the audioContext")
}
let sampleRange: CountableRange<Int> = 0..<audioContext.totalSamples/3
guard let reader = try? AVAssetReader(asset: audioContext.asset)
else {
fatalError("Couldn't initialize the AVAssetReader")
}
reader.timeRange = CMTimeRange(start: CMTime(value: Int64(sampleRange.lowerBound),timescale: audioContext.asset.duration.timescale),duration: CMTime(value: Int64(sampleRange.count),timescale: audioContext.asset.duration.timescale))
let outputSettingsDict: [String : Any] = [
AVFormatIDKey: Int(kAudioFormatLinearPCM),AVLinearPCMBitDepthKey: 16,AVLinearPCMIsBigEndianKey: false,AVLinearPCMIsFloatKey: false,AVLinearPCMIsNonInterleaved: false
]
let readerOutput = AVAssetReaderTrackOutput(track: audioContext.assetTrack,outputSettings: outputSettingsDict)
readerOutput.alwaysCopiesSampleData = false
reader.add(readerOutput)
var channelCount = 1
let formatDescriptions = audioContext.assetTrack.formatDescriptions as! [CMAudioFormatDescription]
for item in formatDescriptions {
guard let fmtDesc = CMAudioFormatDescriptionGetStreamBasicDescription(item) else {
fatalError("Couldn't get the format description")
}
channelCount = Int(fmtDesc.pointee.mChannelsPerFrame)
}
let samplesPerPixel = max(1,channelCount * sampleRange.count / targetSamples)
let filter = [Float](repeating: 1.0 / Float(samplesPerPixel),count: samplesPerPixel)
var outputSamples = [Float]()
var sampleBuffer = Data()
// 16-bit samples
reader.startReading()
defer { reader.cancelReading() }
while reader.status == .reading {
guard let readSampleBuffer = readerOutput.copyNextSampleBuffer(),let readBuffer = CMSampleBufferGetDataBuffer(readSampleBuffer) else {
break
}
// Append audio sample buffer into our current sample buffer
var readBufferLength = 0
var readBufferPointer: UnsafeMutablePointer<Int8>?
CMBlockBufferGetDataPointer(readBuffer,&readBufferLength,nil,&readBufferPointer)
sampleBuffer.append(UnsafeBufferPointer(start: readBufferPointer,count: readBufferLength))
CMSampleBufferInvalidate(readSampleBuffer)
let totalSamples = sampleBuffer.count / MemoryLayout<Int16>.size
let downSampledLength = totalSamples / samplesPerPixel
let samplesToProcess = downSampledLength * samplesPerPixel
guard samplesToProcess > 0 else { continue }
processSamples(fromData: &sampleBuffer,outputSamples: &outputSamples,samplesToProcess: samplesToProcess,downSampledLength: downSampledLength,samplesPerPixel: samplesPerPixel,filter: filter)
//print("Status: \(reader.status)")
}
// Process the remaining samples at the end which didn't fit into samplesPerPixel
let samplesToProcess = sampleBuffer.count / MemoryLayout<Int16>.size
if samplesToProcess > 0 {
let downSampledLength = 1
let samplesPerPixel = samplesToProcess
let filter = [Float](repeating: 1.0 / Float(samplesPerPixel),count: samplesPerPixel)
processSamples(fromData: &sampleBuffer,filter: filter)
//print("Status: \(reader.status)")
}
// if (reader.status == AVAssetReaderStatusFailed || reader.status == AVAssetReaderStatusUnknown)
guard reader.status == .completed || true else {
fatalError("Couldn't read the audio file")
}
return outputSamples
}
E)render使用此函数对音频文件中的数据进行下采样,并转换为分贝：
func processSamples(fromData sampleBuffer: inout Data,outputSamples: inout [Float],samplesToProcess: Int,downSampledLength: Int,samplesPerPixel: Int,filter: [Float]) {
sampleBuffer.withUnsafeBytes { (samples: UnsafePointer<Int16>) in
var processingBuffer = [Float](repeating: 0.0,count: samplesToProcess)
let sampleCount = vDSP_Length(samplesToProcess)
//Convert 16bit int samples to floats
vDSP_vflt16(samples,1,&processingBuffer,sampleCount)
//Take the absolute values to get amplitude
vDSP_vabs(processingBuffer,sampleCount)
//get the corresponding dB,and clip the results
getdB(from: &processingBuffer)
//Downsample and average
var downSampledData = [Float](repeating: 0.0,count: downSampledLength)
vDSP_desamp(processingBuffer,vDSP_Stride(samplesPerPixel),filter,&downSampledData,vDSP_Length(downSampledLength),vDSP_Length(samplesPerPixel))
//Remove processed samples
sampleBuffer.removeFirst(samplesToProcess * MemoryLayout<Int16>.size)
outputSamples += downSampledData
}
}
F)反过来调用此函数获取相应的dB,并将结果剪辑为[noiseFloor,0]：
func getdB(from normalizedSamples: inout [Float]) {
// Convert samples to a log scale
var zero: Float = 32768.0
vDSP_vdbcon(normalizedSamples,&zero,&normalizedSamples,vDSP_Length(normalizedSamples.count),1)
//Clip to [noiseFloor,0]
var ceil: Float = 0.0
var noiseFloorMutable = noiseFloor
vDSP_vclip(normalizedSamples,&noiseFloorMutable,&ceil,vDSP_Length(normalizedSamples.count))
}
G)最后你可以像这样得到音频的波形：
guard let path = Bundle.main.path(forResource: "audio",ofType:"mp3") else {
fatalError("Couldn't find the file path")
}
let url = URL(fileURLWithPath: path)
var outputArray : [Float] = []
AudioContext.load(fromAudioURL: url,completionHandler: { audioContext in
guard let audioContext = audioContext else {
fatalError("Couldn't create the audioContext")
}
outputArray = self.render(audioContext: audioContext,targetSamples: 300)
})
不要忘记AudioContext.load(fromAudioURL :)是异步的.
该解决方案由William Entriken从this repo合成.所有的功劳归于他.
老解决方案
这是一个可用于预渲染音频文件的音量级别而无需播放的功能：
func averagePowers(audioFileURL: URL,forChannel channelNumber: Int,completionHandler: @escaping(_ success: [Float]) -> ()) {
let audioFile = try! AVAudioFile(forReading: audioFileURL)
let audioFilePFormat = audioFile.processingFormat
let audioFileLength = audioFile.length
//Set the size of frames to read from the audio file,you can adjust this to your liking
let frameSizeToRead = Int(audioFilePFormat.sampleRate/20)
//This is to how many frames/portions we're going to divide the audio file
let numberOfFrames = Int(audioFileLength)/frameSizeToRead
//Create a pcm buffer the size of a frame
guard let audioBuffer = AVAudioPCMBuffer(pcmFormat: audioFilePFormat,frameCapacity: AVAudioFrameCount(frameSizeToRead)) else {
fatalError("Couldn't create the audio buffer")
}
//Do the calculations in a background thread,if you don't want to block the main thread for larger audio files
DispatchQueue.global(qos: .userInitiated).async {
//This is the array to be returned
var returnArray : [Float] = [Float]()
//We're going to read the audio file,frame by frame
for i in 0..<numberOfFrames {
//Change the position from which we are reading the audio file,since each frame starts from a different position in the audio file
audioFile.framePosition = AVAudioFramePosition(i * frameSizeToRead)
//Read the frame from the audio file
try! audioFile.read(into: audioBuffer,frameCount: AVAudioFrameCount(frameSizeToRead))
//Get the data from the chosen channel
let channelData = audioBuffer.floatChannelData![channelNumber]
//This is the array of floats
let arr = Array(UnsafeBufferPointer(start:channelData,count: frameSizeToRead))
//Calculate the mean value of the absolute values
let meanValue = arr.reduce(0,{$0 + abs($1)})/Float(arr.count)
//Calculate the dB power (You can adjust this),if average is less than 0.000_000_01 we limit it to -160.0
let dbPower: Float = meanValue > 0.000_000_01 ? 20 * log10(meanValue) : -160.0
//append the db power in the current frame to the returnArray
returnArray.append(dbPower)
}
//Return the dBPowers
completionHandler(returnArray)
}
}
你可以这样称呼它：
let path = Bundle.main.path(forResource: "audio.mp3",ofType:nil)!
let url = URL(fileURLWithPath: path)
averagePowers(audioFileURL: url,forChannel: 0,completionHandler: { array in
//Use the array
})
使用仪器,此解决方案在1.2秒内使用高CPU,使用returnArray返回主线程大约需要5秒,在低电池模式下最多需要10秒.
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