Some ASF and WMV file do not have indexes. That cause seeking issues. You can use VisioForge.Tools.ASFIndexer class to index files.
C# sample usage:
var indexer = new ASFIndexer(); indexer.OnStop += delegate(object o, EventArgs args) { MessageBox.Show("Indexing complete."); }; indexer.OnError += delegate(object o, ErrorsEventArgs args) { MessageBox.Show("Error during indexing: " + args.Message); }; indexer.OnProgress += delegate(object o, ProgressEventArgs args) { Debug.WriteLine("Indexing progress: " + args.Progress); }; indexer.Start(@"c:\samples\sample.asf", VFWMIndexerType.FrameNumbers, 4000, VFWMIndexType.NearestDataUnit);