Offset (plugin) time expression question

[tyshanklin]

Hi all,

I'm using the Offset plugin to cycle an image continually though the comp.  There is a point where I need the cycle to slow down between specific frames, but between the frames where it should be slowing down - it going in the opposite direction really fast.  After passing the second keyframe, the image then moves in the correct direction, at the new slower speed.

The comp is 1920x1080.  On the picture's layer, I've added Offset and a slider control I've renamed to 'Offset Controller'.  On frame 23, there's a keyframe on Offset Controller of -700; on frame 33 theres another keyframe of -100.

I've added an expression to "Shift Center To" on the Offset plugin, which is:

_______________

x=960;

y=540;

[time*effect("Offset Controller")("Slider")+x,y]

_________________

I can't figure out why between those keyframes the picture goes in the opposite direction really fast instead of simply slowing down.  Any help would be greatly appreciated.

[Mike_Abbott]

Essentially what you're trying to do here is change speed over time with an expression. This is difficult due to the fact that expressions have no frame-to-frame memory.  You can read all about it, and find some solutions, here:

https://www.motionscript.com/articles/speed-control.html

[Roland Kahlenberg]

As Mike's said; and I'll add a little - what you're doing is adjusting speed (even if you don't think it's the case). So ... when you have a negative value, you're going to go backwards. Go take a look at Mike's link to Dan Ebbert's writeup and see if you're able to fix your issue. If you're not able to; then post more info here.

[tyshanklin]

Thank you very much Roland and Mike for the information.  I've read the article a couple times, and it's a bit beyond my skills.  I can (on a basic level) understand why the code would break when dealing with rotations (as every 360 degrees it goes back to 0).  My knowledge ends when it comes to translating the information to the 'X' coordinate for position, and understanding it on that side of the problem.

Again - I really appreciate your help.  I know this is a LONG shot, but would you happen to know of a dumbed down version of this article? haha

[Dave_LaRonde]

Why not just use keyframes to simplify the task?

From your description, you don't HAVE to use an expression, you're just using it 'cause it's cool.

[tyshanklin]

Hi Dave,

Thank you for responding.

I will probably use keyframes if I'm unable to figure out the solution.  And you're correct that I "don't have" to use expressions - I choose use them for a couple reasons:

1) It expands my learning.  It's something I don't have the greatest knowledge in, and I prefer to learn instead of growing stagnant in my abilities; it makes me a better compositor. And:

2) For the same reason many people use expressions - because it can save a lot of time in the long run.  Here, I am able to set the speed and not worry about it anymore (or rather - shouldn't have to worry about it anymore).  If I set keyframes, but then need to extend the comp, I will then have to fix the keyframes (on possibly many layers), and then need to figure out how much to change the settings to get it back to the speed it was before.  In some instances - keyframes don't simplify the task; they complicate it.

Though, I do appreciate your thoughts on the subject, I do have a question of my own for you.  I've seen your responses on a number of posts, and I'm having trouble remembering a single instance where your comment offered any actual assistance to the problem being presented; it feels that most of the time it's "go re-film it", "Start over", or in this instance 'just use keyframes'.  It comes off that you're approaching someone who is asking for help, tell them they're out of luck, then insulting them (in this instance - inferring that the only reason I'm trying to use an expression is to be part of the 'cool club').  If you see a post you don't agree with, why not move on?  Go contribute to a topic where you could actually help someone.

[Mike_Abbott · Accepted solution]

Unfortunately I don't think there is a simpler version of the article : )  -  but i feel your pain, this is one of those situations that 'should be simple' but turns out to be anything but.

I'm just wondering about another approach: could you set up your offset animation at a constant speed, precompose that, and apply time remapping to change speed of the procomp?

[tyshanklin]

Mike for the win!  It worked perfectly - though the time-remap made it a bit jittery, so I used Timewarp (set to Pixel Motion) instead, and it's flawless!

What's funny is my co-worker and I were sure there was a simple work around that we were overlooking.  Seriously, though - thank you!

[Mike_Abbott]

Good to hear you got it working : )