What happens when you try to play a video?
What video playback app do you have installed?
Update: Try uninstalling Google+ (or its updates), then reinstalling it, this seems to solve the problem for many users.
The first step to fixing the problem is to force your Samsung device to forget its 'default apps'.
A default app is one which opens automatically when you perform a certain action – like howChrome opens when you tap on an internet link, or your camera opens when you want to attach a photo to a message.
Resetting these preferences won't destroy any data on your phone, but the next time you click a link or add an attachment, you may be asked which app to use as your new default! Follow these steps to clear your app preferences: