Since flass video will be viewed on a compute monitor (most likely) it should be viewed with square pixel dimensions. 720 x 480 DV video is non-square pixels. The square pixel equivalent would be 720 x 534.
By choosing “Maintain Aspect” the encoder believes you want to maintain the non-square pixel dimensions and scales down accordingly.
Using 720 x 534 as the square pixel equivalent to your source clip, you can multiply the dimensions by .75 to get in the ballpark to what you want the Flash video to be.
720 x .75 = 540
534 x .75 = 400.5 (round to 400)
If you want your horizontal frame to be 540 pixels, I would set the vertical size to 400 pixels (with “Maintain Aspect” not checked) and you will have a non distorted image in the final Flash clip.
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Rich Rubasch
Tilt Media