how to redistribute video in own web site

I have a theoretical question: I would know how it's possibile to redistribute videos of another web site , in my web site. I'll try to explain better:

SITE A: Uploads a new video My Site: Recognizes this new upload and create a new video post (linked to the upload of SITE A) in my site.

I think , i should use an API to recognize the upload of new videos , but i also think that my site should have a sort of algorithm to handle this behavior. Can you explain better this thing , or if exist something that i can immediately use to create something similar to this?

thank you