I am a new in programming and opencv as well, I would like to learn it in a perfect way possible. how can I read a video from a file? is there any requirement to do so?

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In general, I would suggest you to start with the basics.

1. If programming is new for you, start by reading a basic book on C++ development, because else you will get stuck into basic programming problems. A good one is the O Reily C++ starter book.
2. Go through the online tutorials of OpenCV one module by a time, it will get you the basics on how to operate on things.
3. If OpenCV is new for you, forget about the 2.x interface and focus immediatly on the 3.1 interface. It is newer, better and has way more bugs fixed :)
4. Once you get the hang of it, get yourself some OpenCV books, with more specified subjects.

In general, also take a look at the FAQ page to have an idea on how to make a decent post. Avoid titles like this who are just way to big and a body of your message that tells close to nothing.

Welcome to the community and good luck with the development!