altering a motion path over time

[Tim Bentley]

It’s not really clear what you want to do – if it’s only a single arrow, why would you need to change the path over time? The arrow can only be at one point at any given time, so changing the path over time is pointless. If you have several arrows, it’s probably much easier to duplicate the path and make changes as needed for each arrow. Or is the path visible, and you want to move it around? In this case you need to set a keyframe for the ‘Path’ value, which will then let you animate the shape over time. It can be fiddly to select / edit individual points (quickest way is to select one of the path properties), and it’s not a method which gives you much control but might be what you’re after.

[Rowan Cloete]

Create a null object and paste the Illustrator path onto it to create a AE mask. The alter the shape of the path, place a keyframe on the mask shape property where you want to the path to start changing. Go the the last position where you want the change to be complete. Reshape the mask here. AE will interpolate to mask shape between these two points to give you a smooth transition of the path. To make the object follow the path, copy this mask’s shape property into the position property of the object. AE will create keyframes of the position over time, that you can manipulate to speed up/slow down the object’s travel (select all position keyframes, hold down alt and drag the last one to drag them all out evenly).

Mac OSX 10.7.4
Mac Pro 3,1
14 gig RAM
GTX580

[Tim Bentley]

Oh I see what the OP meant now (I missed the word jetstream!). Yeah do what Rowan says ↑