Adobe’s web site talks about using 720×534 for square pixel motion graphics …
Work in a square pixel composition. This technique is primarily used to create motion graphics using square pixel source footage when exact positioning is necessary. When After Effects renders the composition, frames appear stretched on-screen, but the final output is correctly proportioned on a DV video monitor. To work in a square pixel composition in After Effects:
1. Create a new composition with the following settings:
— For DV NTSC output:
a. Deselect Lock Aspect Ratio.
b. Type 720 in the Width text box and 534 in the Height text box.
c. Choose Square Pixels from the Pixel Aspect Ratio pop-up menu.
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I’m just doing what Adobe tells me to do! 🙂