如何在 WPF 中向后播放视频？

Question

我想在 WPF 中向后平滑播放视频。我是MediaElement用来播放视频的。我读过这篇文章，其中建议MediaElement.Position定期更改以模仿倒带行为。

我尝试了以下代码来改变位置 MediaElement.Position

private void Button_Click(object sender, RoutedEventArgs e)
{
    mePlayer.Pause();                               //Pause the media player first
    double m = 1 / frameRate;                       //Calculate the time for each frame
    double t = 120;                                 //Total length of video in seconds
    mePlayer.Position = TimeSpan.FromMinutes(2);    //Start video from 2 min
    while (t >= 60)                                 //Check if time exceeds 1 min
    {
        t = t - m;                                  //Subtract the single frame time from total seconds
        mePlayer.Position = TimeSpan.FromSeconds(t);//set position of video
    }
}

在上面的代码中，我试图从 2 分钟到 1 分钟向后播放视频。它给了我 'System.OverflowException' on mePlayer.Position = TimeSpan.FromSeconds(t)。

如果有人知道如何在 WPF 中向后播放视频，请帮助我实现这种效果。谢谢你。

Answer 1

为了顺利完成，您应该使用Timer. 假设帧速率为 24 fps，则意味着每 1/24 = 0.0416 秒或大约 42 毫秒一帧。因此，如果你的计时器每 42 毫秒计时一次，你就可以mePlayer.Position向后移动：

XAML：

<MediaElement x:Name="mePlayer" Source="C:\Sample.mp4"
              LoadedBehavior="Manual" ScrubbingEnabled="True"/>

代码：

    System.Windows.Threading.DispatcherTimer dispatcherTimer;
    int t = 240000; // 4 minutes = 240,000 milliseconds

    public MainWindow()
    {
        InitializeComponent();

        dispatcherTimer = new System.Windows.Threading.DispatcherTimer();
        dispatcherTimer.Tick += new EventHandler(dispatcherTimer_Tick);
        //tick every 42 millisecond = tick 24 times in one second
        dispatcherTimer.Interval = new TimeSpan(0, 0, 0, 0, 42);

    }

    private void dispatcherTimer_Tick(object sender, EventArgs e)
    {
        // Go back 1 frame every 42 milliseconds (or 24 fps)
        t = t - 42;
        mePlayer.Position = TimeSpan.FromMilliseconds(t);
    }
    private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        mePlayer.Play();
    }
    private void Button_Click(object sender, RoutedEventArgs e)
    {
        // Pause and go to 4th minute of the video then start playing backward
        mePlayer.Pause();                               
        mePlayer.Position = TimeSpan.FromMinutes(4);
        dispatcherTimer.Start();
    }