Originally Posted by RogerDH
To make a time-lapse with VirtualDub, you need to set both the frame rate and the "Decimate by" in the box below the frame rate setting. Decimate will throw out the frames you no longer need. If you want to speed the video up by 10, set the frame rate to the original rate x10 (= 300 in the #11), then set the "Decimate by" to 10 so it will only take every 10th frame. (That is, the output file will still have 30 frames per second, but they will be every 10th frame from the original.)
That makes sense, I tried both, but not together.