如何在iOS Swift中更改音频文件的比特率(比特/秒)？

import AVFoundation

func changeAudioBitrate(inputURL: URL, outputURL: URL, bitrate: Float) {
    let asset = AVAsset(url: inputURL)
    let exportSession = AVAssetExportSession(asset: asset, presetName: AVAssetExportPresetAppleM4A)
    
    exportSession?.outputFileType = .m4a
    exportSession?.outputURL = outputURL
    
    let audioSettings = [
        AVFormatIDKey: kAudioFormatAppleLossless,
        AVEncoderBitRateKey: NSNumber(value: bitrate),
        AVNumberOfChannelsKey: 2,
        AVSampleRateKey: 44100.0
    ] as [String : Any]
    
    exportSession?.audioSettings = audioSettings
    
    exportSession?.exportAsynchronously(completionHandler: {
        if exportSession?.status == .completed {
            print("Audio bitrate changed successfully.")
        } else if exportSession?.status == .failed {
            print("Failed to change audio bitrate. Error: \(exportSession?.error?.localizedDescription ?? "")")
        }
    })
}

// 使用示例
let inputURL = URL(fileURLWithPath: "path_to_input_file")
let outputURL = URL(fileURLWithPath: "path_to_output_file")
let bitrate: Float = 128000 // 设置目标比特率，单位为比特/秒

changeAudioBitrate(inputURL: inputURL, outputURL: outputURL, bitrate: bitrate)