AVAssetReaderAudioMixOutput

AVAssetReaderAudioMixOutput.swift

let asset = AVAsset(url: sourceFileURL)
let dict = [AVSampleRateKey:44100, AVFormatIDKey:kAudioFormatLinearPCM] as [String : Any]
assetReaderOutput = AVAssetReaderAudioMixOutput(audioTracks: asset.tracks, audioSettings: dict)

do {
    assetReader = try AVAssetReader(asset: asset)
    if assetReader.canAdd(assetReaderOutput) {
        assetReader.add(assetReaderOutput)
        assetReader.startReading()
    }
} catch  {
    return
}