iMovie question (possibly need a different apple product? IDK) Okay, this question is a bit of a doozy. 
I decided to try my hand at making a rotoscoping animation. That's basically an animation created using real film as a base.  

The original video is 16500 frames long, 24 frames per second. I'm only animating half of those frames. 
I used "FireAlpaca" to draw each and every one of the still images that would be used in this video. 

Do i use imovie to make this video? Obviously since there's less frames, it's going to by quicker, correct ? How do I make it so that there are only 12 frames per second instead of 24, and therefore be able to make my video at the same length as the original film I'm using as the basis for this animation?

Essentially it's just an extremely fast slideshow. Can I do this in imovie? Final Cut Pro? What do I do????
See How can I combine 30,000 images into a timelapse movie?

ffmpeg

In answers to this question the community suggest using the open source tools Avidemux or ffmpeg. For example the ffmpeg approach is:


  This will create a video slideshow (using video codec libx264) from series of png images, named named img001.png, img002.png, img003.png, …
  
  Each image will have a duration of 5 seconds, change the variable according to your choice.

ffmpeg -f image2 -r 1/5 -i img%03d.png -c:v libx264 -pix_fmt yuv420p out.mp4

  
  If your images have four digits, use %04d, etc. If your images do not have this pattern, you can use shell globs, at least on Linux and OS X:

ffmpeg -f image2 -pattern_type glob -i 'time-lapse-files/*.JPG' …

  
  You can also change the output framerate by specifying another -r after the input.


Also see:


ffmpeg: create a video from images
http://electron.mit.edu/~gsteele/ffmpeg/ for a researchers use of ffmpeg to combine individual images into a movie.


Homebrew

You can use Homebrew to get ffmpeg onto your Mac:

ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"


Then install ffmpeg with:

brew install ffmpeg