Michael,
First off, you are assuming that these videos are 16:9.
I’ve dealt with this for years and I have some comments that I think are relevant to the conversation.
First off, I think it’s important to note that the 6 pixel difference between 480 and 486 is so minor that in my testing…you can’t visually see any scaling difference.
Working on AVID back in mid 2000’s, if you exported 16×9 D1 (720×486) from an AVID meridien at square pixels, you’d get a resulting file at 864×486. Working in premier years later, I found 16×9 DV (720×480) footage exported out at square pixels to come out at 853×480. It’s important to note that things seem to have changed around CS3 and CS4. I believe it was CS4 that introduced a new PAR 1.21 instead of the commonly used 1.2 that we had been historically using. Not a huge change, but it seems to have affected things a bit in the translation, I don’t deal in SD anymore, but I just opened Photoshop CS5.5 and the D1 Widescreen square template is 872×486.
My formula that I’ve been using for several years and seems to hold up pretty well:
The 16×9 square pixel translation of 720×480 is 853×480
The 16×9 square pixel translation of 720×486 is 864×486
The 4×3 square pixel translation of 720×480 is 640×480
The 4×3 square pixel translation of 720×486 is 640×480
This is what I use and it has served me well in dealing with archival sources and cataloging older content in a viewable format and aspect.
-Jason