Is there add-on to skip rendering for identical frames? I've googled a lot about it, but everyone suggests to skip them manually. It's not easy.

Maybe there is some add-on or script to make Blender render identical frames only once?
And then I can make the needed frames longer using video editors. It could save many hours of rendering.
Good news, everyone!

I found it! One Canadian guy created the add-on for this. It's called Dopplerender (lol).

Here is more info and link to download: http://creativityhacker.ca/2017/08/08/dopplerender-a-turbo-boost-for-blender-animation-rendering/