I've read the AE CS4 Help, I've watched Chris Meyer's video on lynda.com, and I have questions about the new aspect ratios issue.
Like many, I like to design in a square pixel environment. Let's say I want to create an image with a perfect circle in Photoshop, bring that into AE, then output it. Before, I would have created a 720x540 square pixel image in Photoshop, made my circle, imported that into AE, put it into a 720x540 square pixel comp, done whatever I was going to do in AE, then dragged that comp into an NTSC DV comp (720x480, non-square pixels), hit Command-Option-F to size my nested comp to the new one, and then output the new comp. Would this NOT result in a perfectly round circle on TV?
Should I instead have followed the above process, but substituted "534" for "540" in Photoshop and AE? Would THAT ultimately have resulted in a perfectly round circle on TV?
You're over thinking. It makes no difference what the PAR settings are in your comp as long as the footage is interpreted correctly. If you stick with square pixels in Photoshop and AE interprets the footage as square pixels then no matter what kind of comp you insert the image in, the circle will not be distorted. You can check this by rotating the circle. If it does not wobble then it's round.
What this means is that you can drag any square pixel image or comp into a DV (720X480) normal or widescreen comp and it will be round. Where you are going wrong is using the fit command. This is a dangerous option because it scales X and Y differently distorting the image. Unless you intentionally want to distort an image the X and Y scale values must be identical.
If you want to make your 720 X 540 square pixel image or comp fill a 720 X 480 frame then you'll have to use the fit horizontally shortcut. That is Cmnd/Ctrl + Alt/Option + h so that the X and Y values are identical.
If you're doing this with video then you must have separated fields or you must shift the image down 1 pixel to avoid field reversal.
Again, AE, CS3 and CS4 will perfectly blend, mix, and combine footage and comps with any pixel aspect ratio without distortion as long as you properly interpret the footage. AE will assume that footage created at standard non square pixel frame sizes like 720 X 480 is rectangular pixels. If you did not specifically create or render your images to this size with non-square pixels then AE is going to be wrong and you'll have to change the PAR to square pixels.
If you're having problems the first thing to check is the X and Y scale values. They must be equal.