Reading Image and Video from device in windows phone 8.1

1.  Create a button control in Xaml page.

MainPage.Xaml
 <Button x:Name="btnPhotos" HorizontalAlignment="Left" Margin="2,256,0,0" VerticalAlignment="Top" FontFamily="Arial" Width="388" Height="96" Click="btnPhotos_Click">
            <TextBlock x:Name="textBlock" Text="Photos" FontSize="28" Foreground="#FF7A7070"  Width="210" Height="42"/>
 </Button>
 <Button x:Name="btnVideo" HorizontalAlignment="Left" Height="99" Margin="3,366,0,0" VerticalAlignment="Top" FontFamily="Arial" Width="387" Click="btnVideo_Click">
            <TextBlock Name="textVideo" Text="Video" FontSize="28" Margin="10,0,23,0" Foreground="#FF7A7070" Width="210" Height="42"></TextBlock>
 </Button>

2. Write the following code on code behind.
MainPage.Xaml.cs
========================
 private async void btnPhotos_Click(object sender, RoutedEventArgs e)
        {
            photosProgressBar.Visibility = Visibility.Visible;
            FileOpenPicker openPicker = new FileOpenPicker();
            openPicker.ViewMode = PickerViewMode.Thumbnail;
            openPicker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;
            openPicker.FileTypeFilter.Add(".jpg");
            openPicker.FileTypeFilter.Add(".jpeg");
            openPicker.FileTypeFilter.Add(".png");
            openPicker.PickMultipleFilesAndContinue();
        }

 private async void btnVideo_Click(object sender, RoutedEventArgs e)
        {
            videoProgressBar.Visibility = Visibility.Visible;
            FileOpenPicker openPicker = new FileOpenPicker();
            openPicker.ViewMode = PickerViewMode.Thumbnail;
            openPicker.SuggestedStartLocation = PickerLocationId.VideosLibrary;
            openPicker.FileTypeFilter.Add(".mp4");
            //openPicker.FileTypeFilter.Add(".jpeg");
            //openPicker.FileTypeFilter.Add(".png");
            openPicker.PickMultipleFilesAndContinue();
        }

 public async void ContinueFileOpenPicker(FileOpenPickerContinuationEventArgs args)
        {
            IReadOnlyList<StorageFile> files = args.Files;
            if (files.Count > 0)
            {

                foreach (var item in files)
                {
   //Do your work                  
                }
            }
        }

3. Write an event in App.Xaml.cs.
App.Xaml.cs
===========================
  protected override void OnActivated(IActivatedEventArgs args)
        {
           // Sync osync = new Sync();
            var root = Window.Current.Content as Frame;
            var sync = root.Content as Sync;
            if (sync != null && args is FileOpenPickerContinuationEventArgs)
            {
                sync.ContinueFileOpenPicker(args as FileOpenPickerContinuationEventArgs);
            }
        }