I have a 3D moving object composition with a black background.
I need to export only the object with no background. Like the gray\white checkers background, that allows you to export only the object.
So after that i can plant it in an editing software (without using chroma-key)
In other words - How do i get the gray\white squares neutral background?
You have an preset in your render cue for Lossless With Alpha. That's all there is to it. If you open the video in a media player it will show a black background, but if you import it into a NLE it will have transparency. These are basic AE skills. Please read the help files or search transparent background in the Search Help field at the top right corner of AE to learn more.
Thank you very much.
Indeed, I'm an amature and your advice just put me in the right solution.