如何在WPF中向後播放視頻？

Question

我想在WPF中向後順利地播放視頻。我正在使用MediaElement播放視頻。我讀this post，建議定期更換MediaElement.Position以模仿倒帶行爲。

我嘗試下面的代碼，用於改變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 
    } 
} 

位置。在上面的代碼中我試圖從2分鐘向後播放視頻到1分鐘。 它在mePlayer.Position = TimeSpan.FromSeconds(t)上給我'System.OverflowException'。

如果有人知道如何在WPF中向後播放視頻，請幫助我實現此效果。謝謝。

Answer 1

要做到這一點順利，你應該使用Timer。假設幀速率是24fps，則這意味着每1/24 = 0.0416秒或大約42毫秒是一幀。所以，如果你的計時器滴答每42ms可以向後移動mePlayer.Position：

XAML：

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

代碼：

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(); 
    }