I got a little further on this and then stalled out. In the interest of sharing, here's what else I learned.
Here is a basic run animation, 30 frame motion capture:
Software interpolated to 16 frames:
This works ok, but it's a little bit stiff and floaty because the interpolated frames don't capture the extremes of the joint positions. I took a looking at the original frame by frame, and the timing is a mess. The main problem is that the left and right sides hit the extreme joint positions a frame or two apart.
The body is at its lowest on frame 4, with one foot on the ground and that knee at its most bent position. The other leg, passing underneath, continues to bend until frame 5, after the body has started rising up. The shoulder makes a large move between frames 5 and 6.
Similarly, the figure takes off from the ground on frame 7, but the other knee continues to push forward until frame 8. And so on.
Spreading out the animation to 480 frames and then selecting frames that keep the extreme positions, but as spaced out as I could, gives this:
This looks pretty good. It's not as smooth as the previous animation because it sacrifices timing for position. It looks more bouncy. Over the 16 frames it also spends one more frame on the ground so it looks more grounded rather than floaty.
Time taken for smooth interpolation: a couple of button presses, call it 2 minutes.
Time taken for manual frame selection: approx 20-30 minutes .
That's not a huge difference compared to the time required to slap down all the pixels, so the manual frame selection is probably worth it.
Then into the vector art application! Oh wait, I don't have a vector art application. So I wrote one. It looks like this:
It's similar to Pivot stick animator, but it handles closed forms and curves. This not only lets the user draw an outline on an image, but also add in other flowing lines like hair or clothing without worrying about cloth physics simulators. It's also a clunky, clumsy and unfriendly tool.
Setting up the first frame takes a 30-40 minutes, but simply moving the shapes to the next frame only takes 5 minutes per frame unless the figure changes shape significantly. This doesn't save much time compared to just sketching lines like I did in the first post, but it is a net savings for longer animations (8 frames no, 16 frames yes).
Then to pixels!
And here I stalled out, because I am just too slow at slapping down pixels. I also noticed I had a tendency to simply fill in the vector shapes rather than use them as guides to actually draw. That's no good. If I just filled in the vectors I'd get animated vector art, and then I might as well use pure vector tools instead. I don't really want to do that.
I need to go practice basic pixels and speed pixelling a bit. I declare this effort to be on hold. Hopefully this post is useful for others to learn from my blunders.
Tourist