Some people do hand animation at a lower frame rate to save effort. Obviously, it looks more jerky.
Yes, you can mix items with various frame rates in a single composition.
Do short tests yourself.
I hope you understand that in those discussions of 12fps roto work, they were using progressive images... like cels from an animator or video shot in progressive scan. It doesn't work with video shot at 50i or 60i.
The discussions did not mention anything about what frame rate they were shot at. They just said shoot some video, remove every second frame then import to photoshop to rotoscope.
Ok I need some really clear instructions on this as I dont want to waste any time.
Here is what I intend to do -
I will be shooting at 1080 24fps on a canon 7D.
During the shoot I will have some audio playing out loud so that the actor who Im filming can hear it and lip sync to it.
I will be using some of the footage for rotoscoping so I will remove every second frame then rotoscope it in photoshop.
I will then be bringing the rotoscoped frames(now 12fps) into after effects along with some non rotoscoped footage(24fps) where I will add some effects and sync to the sound track.
Is syncing going to be a problem because I have removed frames? or will it not be noticeable?
If i put the 12 fps footage into a 24fps comp, how does that work? Will it affect it in some way? make it faster etc? Also will this effect the syncing of the audio?
Anything else I need to be aware of before I start?
Deleting every second frame in a roto job depends entirely on the footage. It is not normal technique. Don't take the instructions from YouTube tutorials very seriously unless you know who produced them. There's a lot of misleading information out there and there's a bunch of techniques that are really lousy ways to do things.
Type rotobrush in the Search Help field at the top right corner of AE and follow the links you get to learn about Rotobrush. You'll get better information than you get from YouTube almost every time.
Rick Im not doing roto masking. I am drawing over the top of video. After effects is ok for roto masking but not for roto animation.
The online tuts I learn from are the only way its possible for me to learn anything. Yes theres some crappy ones but theres also some great ones and I know how to discern between them
If your original question contained some more detail we would be better able to give you some help. How are you drawing over the top of video? There are several ways. Animating shape layers? Paint? Stroke effect?
What tutorial were you watching that gave you some trouble? Tell us in some detail about your workflow and what you are trying to achieve and we'll be able to help. In many cases you do not need a new keyframe on every frame, but this depends entirely on how you are trying to animate your drawings, on what kind of shot you are trying to emulate.
Something like this:
or Something like this:
or something entirely different?
If your question is simply a frame rate question, which It may be, then the answer is also simple, and I'm sorry I missed it. If you create a comp at 12 fps, drop in your video at any frame rate, then the video will play in sync and you can do your animation at 12 fps. Then just remove or hide the video, start a new comp that is the same frame rate as the original video, add the video and your animation comp and render away. The 12 fps animation will render at 12 fps and your video will render at the comps frame rate. You may want to turn on frame blending or do some experimentation with CC force motion blur to make the animation look it's best. Both of these videos contain hand drawn animation that was done 1 for 2. IOW, one animation cell was photographed twice, then the next cell was photographed twice. Almost all cell animation has been done that way since they started doing animation. Steamboat Willie to Bugs Bunny, to Who Framed Roger Rabbit.
If you don't mind that the motion will be half as smooth as non-roto work -- in fact, it will look downright jumpy -- I say knock yourself out at 12fps.