avisynth and virtualdub redux

Last time I had used a transform in virtualdub in order to create a video with predominantly white background and a window with a slideshow. This time, did all the processing in avisynth and used virtualdub only to save as avi. Used virtualdub's audio filters for the first time, and had to see this article in order to make them work - we need to add the input and output filters in addition to any other filter we add, and then link them together in a meaningful way.

The main avisynth filter I used was Overlay. Also, Crop to remove unnecessary black bars from one of the videos. The script is as follows, concatenating together three videos with a background pic which has a nice frame on a predominantly white background, as below.

top = BicubicResize(Crop(DirectShowSource("1.mp4"),40,6,-36,-4),320,240,0,0.75)
audio=DirectShowSource("1.mp4")
video1=Audiodub(Overlay(bg, top, 834, 771), audio)

top2 = BicubicResize(DirectShowSource("2.mp4"),320,240,0,0.75)
audio2=DirectShowSource("2.mp4")
video2=Audiodub(Overlay(bg, top2, 834, 771), audio2)

top3 = BicubicResize(DirectShowSource("3.mp4"),320,240,0,0.75)
audio3=DirectShowSource("3.mp4")
video3=Audiodub(Overlay(bg, top3, 834, 771), audio3)

video1 ++ video2 ++ video3