After Effects shows you the original pixels unless you select PAR Correction in the Composition Window. DO NOT Switch the Comp to square pixels. DO NOT change the footage interpretation to square pixels. AE handles PAR correction internally. You must keep the PAR for the footage set to the original PAR.
The option here is to change the comp to 1920 X 1080 square pixels and let AE handle the footage correction. The other option is to keep the project at 1.33 PAR in the comp and turn on PAR correction in the Comp Window. It's the first icon to the right of the views pulldown. Personally, I always prefer to work in square pixels. If you are going to show your completed project on the web then this is mandatory. Understanding pixel aspect ratios is a critical part of your AE education. You either get an A or you fail. There's no half way, and, fortunately, AE will almost always do the right thing if you don't monkey with the footage settings.
Thanks, but need some clarifications here:
This video is for the purpose of broadcasting. What option do you suggest I take?
For Option 1, if I do not switch the Comp to square pixels as you advised, how do I change the comp to 1920 x 1080 square Pixels? Will it switch to square pixels automatically anyway once I change it to 1920 x 1080? Will this change affect the resolution of the video?
For Option 2, I have tried turning on the Toggle PAR Correction on Comp Window. The view appears correct again. When I rendered it out as a .mov file and a .avi file as a test, however, the picture is squeezed again. Anyway I can correct the output too?
Thank you for your help again.
how do I change the comp to 1920 x 1080 square Pixels?
Composition --> Composition settings
Will it switch to square pixels automatically anyway once I change it to 1920 x 1080?
All full HD comps use square pixels. It's in the spec.
Will this change affect the resolution of the video?
The video will automatically fit into the full comp based on AE's automatic footage interpretation rules.
When I rendered it out as a .mov file and a .avi file as a test, however, the picture is squeezed again. Anyway I can correct the output too?
Computers only know square pixels. Creating a square PAR comp will take care of this.
Anyway, you seriously need to read up on this stuff. This is basic everyday stuff and you'll be forever lost without having at least some basic understanding of this.
Your footage has been shot with a camera that doesn't record full 1920x1080, but instead with non-square pixels. Like Mylenium says, read up on this.
I'd import it as 1440x1080 non-square and then drop it into a "Source" comp, and then create a new 1920x1080 square pixel aspect ratio comp and then drop the source comp into this new comp. from then on you'd be working in square pixel 1920x1080.
I'm also guessing that your source is interlaced. What's your intended output? Broadcast or computer screens?