Delete everything except a moving object

[todalina]

For example say I have a stationary video of a butterfly flying around in front of the camera. How do I make it so that the butterfly is all we see and it never leaves the composition?

[todalina]

any ideas guys?

[Roei Tzoref]

tracing over a live video is called Rotoscoping. here's an old but still good article about it: https://www.fxguide.com/featured/the-art-of-roto-2011/

there are several ways to approach this:

1. Masks - Managing and animating shape paths and masks in After Effects

2. Rotobrush tool - After Effects Roto Brush, Refine Edge, and Refine Matte

3. Mocha Ae - it is bundled with your Ae release since CS4 - it's main use is for tracking, but also roto masking. after you roto your element, you can bring the information back to Ae as masks or mocha shape effect : Paste mocha roto shapes to After Effects masks on Vimeo

one cool technique to help better trace your moving object is to use Reverse Stabilization. you stabilize your object, trace it with as minimum keyframes as possible, then re-introduce the motion. here's an example by our community's guru Rick Gerard: Simple Roto - YouTube

you can also show us the footage so we can better assist you by giving specific instructions.

[todalina]

I'm not trying to trace anything. I'm trying to crop out everything but a moving image. I don't want the cropping mask to move around, but rather the video behind it so that it focuses on the thing I choose.

[Roei Tzoref]

if you want to crop a moving image, you need to trace it. The mask will move same as your image thus isolating it from the background. If you could show us the video in question, we can demonstrate the possible techniques and it will probably clear things up,

[todalina]

Ok I think I understand what you mean now. Here is a link to a video for example. Hummingbird eating from a flower - YouTube  Say I want a square composition only around the the bird, so that its head and tail are always at the same spot within the composition (granted in the original video the tail is sometimes out of the picture). My video is of two of my friends kissing, but I want to crop out everything but their respective eye that is recored by the stationary camera. I'd just send that, but they do not want that video online understandably.

[Roei Tzoref]

So you want to stabilize your shot around an object. As if in the original shot, the camera was following the element exactly.  the result would be no motion for the element, and the background would move instead. If so, read this useful thread for various techniques to achieve this result: Re: Tell camera to follow an object?

[todalina]

Ok so I have been struggling with this for so many random reasons even though I know what to do. I am trying to track one eye at a time using the tracking tool than I put that on a null object layer, then I parent a camera to the null and just zoom in. Bam, it should work that simple right? No way this program hates me. One problem is when the tracker gets off of the eye and I need to reset it on the eye and continue "analyzing," but when I reset it everything before that time gets offset by how ever much I moved the tracker. I don't know if it is the tracker doing that or the camera or the null. I can't figure it out. Also out of nowhere I am now having trouble getting a camera to follow the null at all. As a test run I make a null and a camera layer, set the null to 3d and parent the camera to the null, than position the null and move it around through a few seconds, but the camera never budges. The frustrating part is that things like the camera are working fine in one trial than in the next they stop for some reason. Tell me I shouldn't abandon after affects

Ugh thanks for any help...

[Kevin-Monahan]

Hi Todalina,

Sorry you are having trouble with this job. Did you ever solve it? If so, what did you end up doing? If not, let us know how we can help you.

Regards,
Kevin

[Roei Tzoref]

Did you see the camera thread I sent you? Is it a similar issue? Can we see the footage? This would helpma great deal to give you the proper workflow.