Can i put a video background in my 3D viewport ? I know i can do it with a jpg… Can i with a .mov ?
Thanks 
Yes you can
I even had a poor .3gp video I took with my phone, as a background in the 3Dview.
Great! i found the option. go in the camera view, select view menu then background image and there you open your .mov file. turn on the autorefresh option then ALT+a and its done.
This, of course, is a “convenient” specialization of the general notion of compositing, of which “blue screen” is the most familiar cinematic example.
@sundial: not really, because background images do not render. He can only use them as a reference… i hope you know that Atroduli.
In F10, Output tab, BackBuf button enables BackGround image in the render.
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…if you specify the filename in the backbuf filespec field, but just clicking the BackBuf button does not use whatever background image is loaded in a 3d View.
And, the backbuf is just a flat background and any 3D objects that were placed, for example, to line up in Top View will be “out of place” when rendered by a camera at any angle.
Hey, thanks you for your reply !
Hi!
The backbuffer is very slow. I prefer using a plane in background, parented to the camera.
I use the plane like a screen, with the video mapped as Win texture.
The plane must have a shadless material.
Philippe.