Continue Loop

Continue Loop

Sometimes a track point will disappear before the track is
completed, either because it is obscured by a foreground
object or because it has moved offscreen. Mocha can
generally deal with this—if any part of the tracked plane
remains in frame, it is tracked.
Nonetheless it’s useful to do this right in After Effects. First
make certain there are no unwanted extra tracking keyframes
beyond where the point was still correctly tracked;
this expression uses the difference between the fi nal two
keyframes to estimate what will happen next.
Reveal the property that needs extending (Position in this
case), and Alt/Option-click on its stopwatch. In the text
fi eld that is revealed, replace the text (position) by typing
loopOut(“continue”). Yes, that’s right, typing; don’t worry,
you’re not less of an artist for doing it (Figure 8.27).
This expression uses the delta (velocity and direction) of
the last two frames. It creates matching linear motion (not
a curve) moving at a steady rate, so it works well if those
last two frames are representative of the overall rate and
direction of motion.
Chapter 10 offers many more ideas about how to go
beyond these simple expressions and to customize them
according to specifi c needs.