[James Wages]

I myself ignored the math and did it by sight. Here’s how.

I had an SD 4:3 video in FCP7 that I wanted to convert to 720p HD (1280×720). Why? Because putting SD videos on YouTube looks absolutely horrible — you only get decent quality with 720p or (or higher). So within FCP7, I right-clicked on “Sequence 1” and chose “Settings…” I set FRAME SIZE to “HDTV 720p (16:9).” I then set the PIXEL ASPECT RATIO to SQUARE, which will widened my SD clips. To fix the clips, I manually double-clicked each clip and in the MOTION tab I set the SCALE to 150% (which made the top and bottom go to the 720 pixel height), and then I chose an ASPECT RATIO of 7, which fixed the width perfectly (to my eye, anyway).

Yes, there are black bars on the left and right, but since SD isn’t a 16×9 wide format, such is to be expected and I have zero problem with that. I just wanted the top and bottom to fit perfectly in 720p and at the same time make sure the width of each converted SD clip was proportionally the same as what I started with.

I hope this helps.