Buit-in webcam unaveable when use GPU

Hi,

i have a laptop ASUS n550jv with hybrid graphic cards, runnin on Ubuntu 14.04 LTS.
By default it use Intel graphic card and webcam run properly.
But when i switch to nvidia (GEFORCE 550) with Nvidia X Server Settings interface, the webcam
isn’t recognized, even with Cheese software…

At begining, i compiled MioFlow gpu video stream example on codeblock and it work.
But after switch video card to intel and reboot, to test VideoGrabber example (not working with GeForce), and come back to nvidia, Mioflow lost camera connection and turn black screen…

Do i need special driver ?
thank’s

ps: not clear, but i only find this article mentioning this problem.