Hey justabloke616,
It sounds like you're having an issue with videos on your MacBook Pro in a web browser. To make sure we fully understand, you will see a green box instead of a video preview, but as soon as you hit play, the video works fine. Does that sound correct? If yes, does this happen in multiple web browsers or a specific web browser? Additional details can help us determine what might be going on, and help us also provide steps to help.
Does quitting and restarting your web browser help? You can also see if restarting your MacBook Pro helps: Log out, sleep, wake, restart, or shut down your Mac It may seem like a simple step, but it can sometimes resolve issues.
Another thing, if you are using Safari, you can remove any extensions in Safari in the menu bar > Preferences > Extensions tab. You can then add those back one by one and test to see if this issue continues.
Take care.