SL中MediaElement（视频播放）

<UserControl x:Class="SL1.SLMedia"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400">
    
    <Grid x:Name="LayoutRoot" Background="White">
        <MediaElement x:Name="mePalyer" MinWidth="1"  Source="vedio/1.mp4" Margin="0,0,0,50" MediaOpened="mePalyer_MediaOpened"></MediaElement>
        <Button x:Name="btnPlay" Content="播放" VerticalAlignment="Bottom" HorizontalAlignment="Left" Margin="20,20"  FontFamily="Arial Black" FontSize="25" Click="btnPlay_Click"></Button>
                <Button x:Name="btnStop" Content="暂停" VerticalAlignment="Bottom" HorizontalAlignment="Left" Margin="100,20"  FontFamily="Arial Black" FontSize="25" Click="btnStop_Click">
        </Button>
        <ProgressBar x:Name="pbTimer" HorizontalAlignment="Left" Height="35" Margin="180,245,0,20" VerticalAlignment="Bottom" Width="210" Minimum="1"  Loaded="ProgressBar_Loaded_1" />

    </Grid>
</UserControl>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Windows.Threading;

namespace SL1
{
    public partial class SLMedia : UserControl
    {
        public SLMedia()
        {
            InitializeComponent();
        }

        private void btnPlay_Click(object sender, RoutedEventArgs e)
        {
            mePalyer.Play();
        }

        private void btnStop_Click(object sender, RoutedEventArgs e)
        {
           // mePalyer.Stop();
            mePalyer.Pause();
        }

        private void ProgressBar_Loaded_1(object sender, RoutedEventArgs e)
        {
         
        }

        void tick_Tick(object sender, EventArgs e)
        {
           // pbTimer.Value += 3;
            pbTimer.Value= mePalyer.Position.TotalMilliseconds;
        }

        private void mePalyer_MediaOpened(object sender, RoutedEventArgs e)
        {
            pbTimer.Maximum = mePalyer.NaturalDuration.TimeSpan.TotalMilliseconds;       
            DispatcherTimer tick = new DispatcherTimer();
            tick.Tick += tick_Tick;
            tick.Interval = TimeSpan.FromMilliseconds(500);
            tick.Start();
        }

      
    }
}