Version 2.78, 3D view, Problems displaying a movie clip as background, how to fix it? I am using Blender Version 2.78,
in the default layout I did the following:


1 to go into front view
space to enter command: allign camera to viewport
n to open the box on the right
selected image>movie clip 


However no movie clip showing up, I tried both orthographic and perspective mode, inside and outside the camera. 
When I open an image as a background, it shows up on pressing 7 on the numpad. The movie clips I tried to open as background images already worked in blender inside the video sequence editor.
This is what I meant in comments above (if I got what you meant)

As said


also selecting "image" you can select a movie file, it should work anyway
or, using "movie" option, try disabling "camera clip" and select again the video through the "open" button