How to mask a moving object from a video and add to another background

[Yatindra5E12]

Can anyone help me with this scenario in an easy way.

I have a video of a cat playing. I just want to take that playing cat out of that video and add it to a different background image. 

So ultimately what i want is a cat playing in a different background than the actual footage of the video.

Thank you!

[Rick Gerard]

The most efficient workflow depends entirely on the shot. Rotobrush is a semi-automated tool that will work fairly well if there is sufficient contrast between the subject (the cat) and the background. Sometimes you have to combine techniques. You may be able to use channel effects or levels to create a matte. You may need to create masks and animate them by hand. 

If you want to remove the background from a shot that was not shot with removing the background in mind it can and often does take a lot of time. I've worked on 3-second shots that took the better part of a day. I've used Rotobrush on 10-second shots that took less than a half-hour. Show us a screenshot of the footage*, or better yet, show us the footage and we can point you to a solution. Any technique you use is going to require a good understanding of the UI and standard workflow in After Effects. 

* The "Drag & Drop here..." area is buggy and should not be used to share images. Please use the toolbar or just drag your images to the reply field.

[PieterEgriega]

I too am keen to take action out of the background so that I can build projection mapping animations around my actions and then remove me, so that when I project my animations I then perform live the actions I performed in the original movie. I'm doing my first one, which is a 3m30s piece using rotobrush but I haven't propogated more than 30s and its still taken half a day....there must be a quicker way?

[Rick Gerard]

Roto in any form was never intended to be used on long shots. Rotoscoping in any form is a tedious, time-consuming task implemented when you cannot design the shot to make other techniques of creating a matte (transparency) much more efficient. The Rotobrush tool does simplify the process a bit, but it is still slow and requires a lot of careful monitoring and cleanup unless the scene is carefully planned and photographed with Roto in mind.

I would split the layer you are trying to Roto into sections that are only about 10 seconds long and Roto each section. 

PieterEgriega, start a new thread and embed* a screenshot of your footage, and maybe we can suggest a more efficient workflow. I rarely run Rotobrush on the original footage. The original is duplicated and pre-composed, so it is the only thing in the new comp. It is then often pre-composed again to add masks, procedural mattes, color correction, or other effects rotobrush job more efficiently. 

* The "Drag & Drop here..." area is buggy and should not be used to share images. Please use the toolbar or just drag your images to the reply field.