If your images are the same size as a standard non-square pixel video format like 720 X 480, After Effects will assume that the images are rectangular pixels. Check the file interpretation of the images.
If your composition settings are for non-square pixels then the frame size is wrong for any kind of digital distribution to the public. Your comp needs to be square pixels and a square pixel frame size like 1920 X 1080. Media players do not usually know how to interpolate non-square pixel formats.
The only reason to work in a non-square pixel format like DVC Pro is to lay the rendered footage back to tape. Not many people use tape anymore. No broadcaster uses non-square footage anymore.