WPFで動画ファイルを再生するサンプル

<Window x:Class="VideoPlayer.MainWindow"
        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"
        xmlns:local="clr-namespace:VideoPlayer"
        mc:Ignorable="d"
        Title="MainWindow" Height="720" Width="1280">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>

        <StackPanel Orientation="Horizontal" Grid.Row="0" HorizontalAlignment="Center">
            <TextBox x:Name="MovieFileTextBox" Height="30" Margin="10" Width="1000"></TextBox>
            <Button x:Name="FileSelectButton" Height="30" Margin="10" Width="100" Click="FileSelect">ファイル選択</Button>
        </StackPanel>
        <MediaElement
            x:Name="MovieControl"
            Grid.Row="1"
            LoadedBehavior="Manual"
            UnloadedBehavior="Stop">
        </MediaElement>
        <StackPanel Orientation="Horizontal" Grid.Row="2" HorizontalAlignment="Center">
            <Button x:Name="PlayButton" Height="30" Width="100" Margin="10" Click="PlayClick">再生</Button>
            <Button x:Name="PauseButton" Height="30" Width="100" Margin="10" Click="PauseClick">一時停止</Button>
            <Button x:Name="StopButton" Height="30" Width="100" Margin="10" Click="StopClick">停止</Button>
        </StackPanel>
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using Microsoft.Win32;

namespace VideoPlayer
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
        public void FileSelect(object sender, EventArgs e)
        {
            var d =new OpenFileDialog();
            d.InitialDirectory = @"c:\";
            d.ShowDialog();
            MovieFileTextBox.Text = d.FileName;
            MovieControl.Source = new Uri(MovieFileTextBox.Text);
        }
        public void PlayClick(object sender, EventArgs e)
        {
            if (MovieFileTextBox.Text == "") return;
            MovieControl.Play();
        }
        public void PauseClick(object sender, EventArgs e)
        {
            MovieControl.Pause();
        }
        public void StopClick(object sender, EventArgs e)
        {
            MovieControl.Stop();
        }
    }
}