如何在 swift 中将 .caf 音频文件转换为 .mp4 文件

Question

我正在使用带有AVAudioRecorder 的设备麦克风录制音频，它返回.caf 格式的文件，该文件只能在Apple 设备上播放，而不能在Android 设备上播放。由于 Apple 不支持 .mp3 文件，所以我想在上传到服务器之前将其转换为 .mp4 格式。 .mp4 是否仅适用于音频？我可以用AVAssetExportSession 转换它吗？

以下是录音机代码：

func setupAudioRecorder ()
    {

    let fileMgr = FileManager.default
    let dirPaths = fileMgr.urls(for:.documentDirectory,
                                in:.userDomainMask)

    let soundFileURL = dirPaths[0].appendingPathComponent("myaudio.caf")

    let recordSettings =
        [AVEncoderAudioQualityKey: AVAudioQuality.min.rawValue,
         AVEncoderBitRateKey: 16,
         AVNumberOfChannelsKey: 2,
         AVSampleRateKey: 44100.0] as [String : Any]

    do {
        try audioSession.setCategory(
            AVAudioSessionCategoryPlayAndRecord)
    } catch let error as NSError {
        print("audioSession error: \(error.localizedDescription)")
    }

    do {
        try audioRecorder = AVAudioRecorder(url: soundFileURL,
                                            settings: recordSettings as [String : AnyObject])
        audioRecorder?.prepareToRecord()
    } catch let error as NSError {
        print("audioSession error: \(error.localizedDescription)")
    }
}

Answer 1

经过大量搜索，我可以使用这段代码将 .caf 转换为 .mp4

    let audioURL = ".caf audio file url"

    let fileMgr = FileManager.default

    let dirPaths = fileMgr.urls(for: .documentDirectory,
                                in: .userDomainMask)

    let outputUrl = dirPaths[0].appendingPathComponent("audiosound.mp4")

    let asset = AVAsset.init(url: audioURL)

    let exportSession = AVAssetExportSession.init(asset: asset, presetName: AVAssetExportPresetHighestQuality)

    // remove file if already exits
    let fileManager = FileManager.default
    do{
        try? fileManager.removeItem(at: outputUrl)

    }catch{
        print("can't")
    }


    exportSession?.outputFileType = AVFileTypeMPEG4

    exportSession?.outputURL = outputUrl

    exportSession?.metadata = asset.metadata

    exportSession?.exportAsynchronously(completionHandler: {
        if (exportSession?.status == .completed)
        {
            print("AV export succeeded.")

           // outputUrl to post Audio on server

        }
        else if (exportSession?.status == .cancelled)
        {
            print("AV export cancelled.")
        }
        else
        {
            print ("Error is \(String(describing: exportSession?.error))")

        }
    })

Answer 2

您可以直接在 MPEG4 AAC 中录制，无需额外的转换步骤。使用 AVFormatIDKey 和 kAudioFormatMPEG4AAC 值并将采样率降低到 8000 或 16000。