从Library.AssetForUrl（）获取字节数组

Question

我尝试使用下面的代码块将视频保存到图库，之后将此视频作为字节数组。我无法理解Library.AssetForUrl（）部分是如何工作的。如何从中获取字节数组？

 var Library = new ALAssetsLibrary();
    albumSave = await Library.WriteVideoToSavedPhotosAlbumAsync(outputFileUrl);
    Library.AssetForUrl (assetUrl, delegate(ALAsset asset) {
        long size = asset.DefaultRepresentation.Size;
        Console.WriteLine("Filename: " + asset.DefaultRepresentation.Filename);
        byte[] imgData = new byte[size];
        NSError nsError;
        IntPtr buffer = Marshal.AllocHGlobal(imgData.Length);

        asset.DefaultRepresentation.GetBytes(buffer, 0, (uint)size, out nsError);
        Console.WriteLine(nsError);
       Marshal.Copy(buffer, imgData, 0, imgData.Length);
    },
    (NSError err)=>
    {
    Console.WriteLine(err);
    }