DVDs are 720x576 with anamorphic pixels. There's no way around that. You need to scale the output e.g. by using the respective options on teh Render settings panel or nesting the comp.
Well where should I start? AE will allow you to use square pixels. In fact the 1280 X 720 frame size is the HDV/HDTV 720 P preset and it's square pixels.
You don't set the compression until you render and, if you want the highest quality, you don't render MPEG formats of any kind using the Render Cue, you export them using the Adobe Media encoder. Where is After Effects telling you you can't use MPEG2??? How are you trying to get there.
If you are going directly to Premiere Pro (Which only exports or renders using the Adobe Media Encoder) you don't even need to render, you can just import your AE Composition into PPro.
Secondly, A DVD is not High Def in any form. DVD's are all 720 X 480 pixles (in NTSC countries). The only options are widescreen or normal.
Please read the sections on Rendering in the help files.
Thanks Rick. this solves my after effects problem. I guess the real problem i'm having is i'm downgrading this 1920 x 1080 footage out of premiere to 720x480 and it looks awful, kind of pixelated.. my sequence matches my footage.. i'm not sure why it's not looking so good. Also, my computer is pretty slow and it's taking FOREVER to render out my project.. like 8 hours...
Should i export my project from premiere as 1280x 720 and then make a NEW premiere project, THEN export that at 720x480? or is that going to be too much compression?
I think if i try to render a project for 8 hours.. my computer will explode....
I'm just guessing that you want to burn a DVD. If so, just take your Premiere Pro proejct or your After Effects project into Encore and build your DVD using the HD footage.
If you are trying to playback 720 X 480 (I'm assuming wide screen) on a modern flat screen or computer monitor then it's going to look pixelated and not very high quality, just like playing a DVD does. There are very few new videos on YouTube that are not at least 720P HD. That's nearly 4 times the resolution of your intended output.
The way to get the best quality is to use the best encoding and compression for the format. For a DVD that means Encore at a minimum, not AE's output module. Please let us know what you are planning do to with the video so we can point you in the direction of the highest quality final output.