Hi,
Ideally you should create the HD comp first, render that and then drop it into an NTSC comp afterward.
But if you’ve already created the NTSC comp and need to resize to HD, you may have a lot of work ahead of you. It is possible you could get away with dropping your NTSC comp into an HD comp and hit the “continuously rasterize” switch, but this only works for pretty simple situations and it can defeat certain effects.
I get the impression you’ve already finished the NTSC version, but if you are just getting started, the following might help…
The simple answer is assuming you just need an NTSC version of the HD, all you really have to do is create and render the animation in HD and then bring it back into AE and drop it into an NTSC comp and render that.
But…
If your frame rate is 24fps, this is not a bit deal if you don’t mind the 3/2 pull down that gets added when converting to 30fps interlaced. Generally this isn’t objectionable since people are used to that look.
There is the problem of 16×9 vs. 4×3. If you need a 4×3 version, the simplest solution is to protect the sides of the frame in HD so that when you crop them off, you don’t lose anything critical. For example don’t extend and text or important image elements beyond that 4×3 space. The problem here is that it scarifies optimum composition for flexibility. If the company doesn’t need 4×3, then there’s no problem.
Of course the alternative is to create a version with framing for 4×3. You can keep it in HD so as to not have to deal with resizing everything, but then drop that comp into a 4×3 NTSC comp. Of course being HD, your render will be longer, but probably not as long as resizing everything.
There is also the issue of proper levels for broadcast NTSC vs. HD. Again, it is better to start in the broader color space of HD and downconvert to NTSC setting black to 16 and white to 235 for output to video.
But if you’ve already finished the NTSC version, I don’t know that there’s much else to do but go through the tedious task of rebuilding it in HD.
If anyone else has any suggestions I’d like to hear them too.
Hope this helps,
Lars