VirtualDub's resize filter can do it. Just make sure that the borders (and by extension, the viewable area) are both multiples of 16 - i.e. for true 16:9 footage, get the viewable area to 640x352 and add 64-pixel borders to the top and bottom. The explanation for this (because by VDMod_Resize's calculations it would normally be 640x368) is because having the border between letterbox and actual footage in the middle of a macroblock causes garbage at the edges. A height of 368 would make even borders on a 480-height video be 56 pixels each - 3.5 16x16 macroblocks, which causes problems. 352 makes it an even 4, and solves that issue (it also technically makes the image 9:5 ratio instead of 16:9, but most people can't really tell the difference).
The regular resize filter handles this by enabling the Letterboxing option, just input the intended height.
Example:
I don't know whether WMM natively lets you work with 640-width images, though (actually, not so much that it won't let you work with them, but moreso whether it'll let you
export them, since it's always a good idea to export at the dimensions of your source rather than let the editing program do any resizing - that's the job of postprocessing software). If you need them in 720-width, just change the width value on the top.
But generally, yes, AviSynth would be the easier option, as it would only require a script like, say:
Code: Select all
AVISource("test.avi").LanczosResize(640,352).AddBorders(0,64,0,64)
And then you'd just have to export that from VirtualDub as another AVI (or make a fake AVI with whatever tool does that, but I generally distrust stuff like that).
All of that is assuming you're working with anamorphic footage rather than video that's already letterboxed.
