Assuming that your 16:9 footage is also SD (if it’s HD, you might be able to drop it into a 4:3 sequence and resize accordingly such that you can get a full-screen center crop going without losing resolution)…
If you drop an anamorphic 16:9 SD clip into a 4:3 sequence, you will get the letterbox. It’s got to do with how the pixel aspect ratio allows you to shoot 16:9 SD footage.
If you want the 16:9 footage to fill up the 4:3 screen, you’ll need to blow up the footage by increasing the size. But this means you’ll lose resolution/quality.
Since you’re going to DVD, why don’t you continue working on a 16:9 anamorphic sequence, output to compressor & author through DVD Studio Pro. You’ll be able to burn a DVD that’ll fill the screen on a widescreen TV or automatically letterbox itself on a 4:3 TV.
Kai
FCP Editor / Producer with Intuitive Films
https://kai-fcp-editor.blogspot.com
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