I'm trying to Import some HD clips into an 4:3 SD project with letterboxing. I notice when I import the HD clips, I can't seem to get the Pixel Aspect Ratio or the Image Aspect Ratio to match the project. The project currently shows "unknown" under Pixel Aspect Ratio and Image Aspect Ratio for all of the SD (and HD) clips in it, I suspect it's supposed to be this way. But upon my Import of new/additional HD clips, it says the Pixel Aspect Ratio is 1.841 and the Image Aspect Ratio is 4:3 (because it's now letterboxed into the 4:3 frame).
Is the Pixel Aspect Ratio supposed to be this way? What am I doing wrong, if this is not right?
Avid does not really care about aspect ratio. It only renders titles / certain wipes in the correct aspect ratio if you set it.
So, you're bringing in your stuff at original pixel size, and you need to set the correct scaling / cropping / aspect ration yourself.
There are presets in the effect palette to do so, so no worries there.
(but since it's HD, you might want to customize the downscaling / letterboxing a bit by reframing.)