> I need to grab thumbnails from a video file with extension wmv or dat.
> I need to write the code in c#
>
> has anybody done this before.
I recommend you Google "DirectShow .NET". There's an open source project
named that designed for allowing the use of DirectShow from .NET
applications. You can get a thumbnail frame from a valid video file
(don't know whether ".dat" qualifies, since that's a pretty generic file
extension) using the IMediaDet interface (if I remember the name
correctly...if I don't, it's something like that :) ).
Pete