1. When I open a new composition, I have to choose the height and width. How do I know what they're supposed to be?
Entirely depends on your target output spec and your workflows. Obviously one would pick a HD preset for TV playback, other presets for other stuff. This could be identical to the input source, but not necessarily. All the same nothing stops you from creating arbitrary comp sizes when they are needed e.g. for nested comps during project creation. It's not uncommon to create e.g. towel-long/-wide compositions for all sorts of scrolling, parallax and panorama effects just as for instance particle effects may want a square aspect comp of small pixel size to be used as a custom particle shape. Beyond what I said in the first sentence thus there cannot be a definite answer set in stone.
2. Once I've imported a video file and successfully... [snip]
Erm, well... You know, I'd yell in your face if you stood in front of me. Sorry, but there's no other way to say it, but this is simply a "Why oh why don't people read the help?" thing. How AE's preview and caching system works is elaborately explained there, including what those fancy colors mean.
What am I missing or doing wrong here?
As per the above: Not reading the help files is your biggest neglect.
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I'm very new to AE, and I've basically learned by doing,
You seriously cannot learn to use After Effects that way. It is way too complicated.
as opposed to sitting through endless tutorials that don't give me the answers to my specific questions.
You might not need to go through a tutorial on Rotoscoping to do what you want to do, but, dude, you seriously need to get a foundation in the basics of how AE works at the very least.
You are approaching AE like it's a video editing program and it is not. Please do yourself a huge favor and go through some of the basics at least.
This is a good resource for starting off.
If you don't want to take the time to learn how to use After Effects, perhaps you should look into using something aimed less at professionals.
1 person found this helpful
Just to add to the comments above -- don't learn AE by doing. Many have tried. All have failed. Bite the bullet. Look at the Help and look at the tutorials.
Mylenium, Sazalam, and Dave:
Thanks for the replies! I realized after I posted this that I probably sounded like a smartass, claiming that I don't need tutorials and can get by just with trial and error and asking people here questions. (Hey, I learned iMovie by myself, so what could be so difficult about After Effects? (snicker))
Now I know that I do need to invest the time if I want to get anything done. And I know that will be time well spent. I did have some one-one-one help last year with another project, so I figured that was all I needed to know. But really, I was just scratching the surface then.
Excuse me, I need to go watch a tutorial and check some help files. Later!