I’m using 2.47 and can’t figure out a good way around this problem and couldn’t find an answer searching this forum.
I have an AVI of 1341 frames that works fine in some areas of the program, but not where I really need it. When I load the AVI in to the Output “backbuf” it usually won’t update. It simply shows a static image for all frames while updating the foreground objects.
The AVI frames update fine when I load them in to the 3D display’s “Background Image” or in an image node or as a texture on a plane.
I don’t like the last two options because I give up too many advantages I like. Nodes, as far as I can tell, does away with the ability to automatically rotoscope using objects which allow the background image to show through. You can’t have an object show only a shadow either. You CAN do both, but only with oodles of rendering layers and various compositing options and no immediate feedback.
A plane with AVI texture is too hard to line up to match the 3D display’s “Background Image” and you have to make sure the aspect ratio is right. Besides, the picture quality is sub-par. Lots of detail is lost.
I’ve verified the project length is the same length as the AVI.
I’ve tried all sorts of permutations of Output button settings.
I’ve tried different compression schemes.
I can’t find “Auto refresh” for the Output tab’s backbuf, nor can I find where to enter the number of frames.
Why can’t the background image automatically update the project output settings (frame size, aspect ratio & frame rate) and also show up as a background image in the Camera’s preview window? You get what you pay for? 
Thanks in advance for your help!