A couple of things come to
mind:
1) Is the footage meant to be 4:3 or 16:9? AE may be doing an anamorphic 'unsqueeze' to stretch the image to 16:9. By default the scaling quality is low so you'll see subtle blockyness. This is just the preview quality and if you disable the Pixel Aspect Ratio correction in the Comp Window the image should look better.
2) Is the footage interlace or not? AE may be Separating fields which will also result in reduced resolution in the Comp Window. If the footage is progressive disable fieldseparation in the Footage Interpretation Window.
3) Is your preview resolution set to 100%? (dropdown in Comp Window)
Hope this helps,
Barend
Raamw3rk - digital storytelling and visual effects
