On seconds thoughts, it might be a bit more complicated than I first thought i.e. depending on what you want to achieve.
It really depends on how you wish to add the stickers to the video. If it is just an overlay (such as a gif, picture, text or even another video) then it should be possible with my ffmpegencoder library.
If you want that the sticker to be "attached and synced" with an object in the video (like in your sample or like when glasses are shown on a face or similar), then this would probably involve some computer vision. For this, there is a library called OpenCV by @JordiCP which is available here. You could also use the ffmpegencoder library for this but it means you would need to analyze the video and decide where and when to attach your sticker as an overlay before saving and encoding the new output video. Also, even if you used only OpenCV for this, you would still probably want to post-process the video so ffmpegencoder might still be needed.
I have in mind also other ways this can be done but for performance what I described above is probably the best approach.