Creating WP8 in-app video is not generating a .jpg thumbnail - vb.net

Question

I've been told that when I allow the user to create a video from within my app, a .jpg thumbnail image is supposed to be generated automatically. However, using windows phone power tools, I can see that only the video is generated, no image. Here is the code below:
EDIT: the QUESTION here, is HOW does one GET a thumbnail image from a given video that is saved in isolated storage?
' Set recording state: start recording.
Private Async Sub StartVideoRecording()
Try
App.ViewModel.IsDataLoaded = False
'isoStore = Await ApplicationData.Current.LocalFolder.GetFolderAsync("IsolatedStore")
strVideoName = GenerateVideoName()
isoFile = Await isoVideoFolder.CreateFileAsync(strVideoName, CreationCollisionOption.ReplaceExisting)
thisAccessStream = Await isoFile.OpenAsync(FileAccessMode.ReadWrite)
Await avDevice.StartRecordingToStreamAsync(thisAccessStream)
'save the name of the video file into the list of video files in isolated storage settings
Dim videoList As New List(Of InfoViewModel)
isoSettings = IsolatedStorageSettings.ApplicationSettings
If isoSettings.Contains("ListOfVideos") Then
videoList = isoSettings("ListOfVideos")
Else
isoSettings.Add("ListOfVideos", videoList)
End If
videoList.Add(New InfoViewModel With {.Name = strVideoName, .DateRecorded = Date.Now})
isoSettings("ListOfVideos") = videoList
isoSettings.Save()
isoSettings = Nothing
' Set the button states and the message.
UpdateUI(ButtonState.Recording, "Recording...")
Catch e As Exception
' If recording fails, display an error.
Me.Dispatcher.BeginInvoke(Sub() txtDebug.Text = "ERROR: " & e.Message.ToString())
End Try
End Sub

Answer 1

In Windows Phone 7.0 it wasn't possible using the "official" SDK to access the camera other than using CameraCaptureTask. But using Microsoft.Phone.InteropServices library it was possible to create a custom camera view in the application. If you used this VideoCamera class, it had an event called ThumbnailSavedToDisk, which might be what you have heard about. But apps using Microsoft.Phone.InteropServices was never allowed in the Windows Phone Marketplace. You can read more about it here.
To generate a thumbnail from a video file one solution would be to read up on how the MP4 file format works and extract one of the frames and use that as a thumbnail. Unfortunatly I haven't found any libraries that can do this.
Another, but far from optimal solution, would be to play the video in a MediaElement and then render that Control to a bitmap. This can be done with the following code (written in XAML/C#, I don't know VB.net, but should be easy to port):
<MediaElement
x:Name="VideoPlayer"
Width="640"
Height="480"
AutoPlay="True"
RenderTransformOrigin="0.5, 0.5"
VerticalAlignment="Center"
HorizontalAlignment="Center"
Stretch="Fill"
Canvas.Left="80"/>
And then to create the thumbnail:
// Set an event handler for when video has loaded
VideoPlayer.MediaOpened += VideoPlayer_MediaOpened;
// Read video from storage
IsolatedStorageFileStream videoFile = new IsolatedStorageFileStream("MyVideo.mp4", FileMode.Open, FileAccess.Read, IsolatedStorageFile.GetUserStoreForApplication());
VideoPlayer.SetSource(videoFile);
// Start playback
VideoPlayer.Play();
And then create the event handler which "captures" the thumbnail:
void VideoPlayer_MediaOpened(object sender, RoutedEventArgs e)
{
Thread.Sleep(100); // Wait for a short time to avoid black frame
WriteableBitmap wb = new WriteableBitmap(VideoPlayer, new TranslateTransform());
thumbnailImageHolder.Source = wb; // Setting it to a Image in the XAML code to see it
VideoPlayer.Stop();
}
Here is how it looks when using a modified version of the Video Recorder Sample. (The small image with the blue border in the upper right corner is the thumbnail of the recorded video. Behind is the camera Viewer.)