Recently both Instagram and Twitter (Vine) has launched there own video service which allows you to record and share short videos,
Creating videos is very simple and you can share them on your timeline like you share images earlier. But in Instagram when you open up your profile and if your friends has shared videos then it will be played automatically when you scroll down.
This is annoying as it distract you and you could miss any important thing. If you too wanna disable it then here is a simple tweak.