如何从xamarin格式的视频中生成缩略图

using System;
using System.IO;
using Xamarin.Essentials;
using Xamarin.Forms;

namespace ThumbnailGenerator
{
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
        }

        private async void GenerateThumbnailButton_Clicked(object sender, EventArgs e)
        {
            try
            {
                // 选择视频文件
                var pickedFile = await FilePicker.PickAsync(new PickOptions
                {
                    FileTypes = FilePickerFileType.Video
                });

                if (pickedFile != null)
                {
                    // 获取视频文件路径
                    string videoPath = pickedFile.FullPath;

                    // 创建 MediaSource 对象
                    var mediaSource = MediaSource.FromFile(videoPath);

                    // 设置 MediaElement 的源
                    mediaElement.Source = mediaSource;

                    // 等待视频加载完成
                    await mediaElement.PlayToCompletionAsync();

                    // 获取视频的总时长
                    TimeSpan videoDuration = mediaElement.Duration;

                    // 将视频的播放位置设置为中间位置
                    TimeSpan thumbnailTime = videoDuration.TotalSeconds > 2 ? TimeSpan.FromSeconds(videoDuration.TotalSeconds / 2) : TimeSpan.Zero;
                    mediaElement.Position = thumbnailTime;

                    // 获取当前视频帧作为缩略图
                    var thumbnailImage = await mediaElement.TakeSnapshotAsync();

                    // 停止视频的播放
                    mediaElement.Stop();

                    // 保存缩略图
                    string thumbnailPath = Path.Combine(FileSystem.CacheDirectory, "thumbnail.jpg");
                    File.WriteAllBytes(thumbnailPath, thumbnailImage);

                    // 显示缩略图
                    thumbnailImageSource.Source = ImageSource.FromFile(thumbnailPath);
                }
            }
            catch (Exception ex)
            {
                // 处理异常
                Console.WriteLine($"Error: {ex.Message}");
            }
        }
    }
}