Audio 如何在WindowsPhone8中将音频文件格式化为aac？

我想将音频文件保存为.aac格式并发送到iPhone：

private string fileAudioName;
private IRandomAccessStream randomAccessStream;
private AudioVideoCaptureDevice mic;
private DispatcherTimer dtm;

private async void RecordAudio()
{
    try
    {
        await MicStartAsync();
        await StartRecordingAsync();
        mic.AudioEncodingFormat = CameraCaptureAudioFormat.Aac;
        dtm.Start();
        _sw.Reset();
        _sw.Start();
        isRecording = true;
    }
    catch (Exception ex) { }
}

public async Task MicStartAsync()
{
    mic = await AudioVideoCaptureDevice.OpenForAudioOnlyAsync();
}

public async Task StartRecordingAsync()
{
    await CreateFileStreamForAudioAsync(fileAudioName + ".aac");
    await mic.StartRecordingToStreamAsync(randomAccessStream);
}

但当我把这个音频文件发送到iPhone后，iPhone就无法读取了