Here's my theory, based on the evidence at hand. In the render settings, the max. texture size is defaulted at 1024. For some reaosn (and this is the bit I cant' explain), this is causing the background movie to be resized. Although the preview window/document size is being resized to the full size of the movie, the longest side of the movie is being changed to 1024 (and the other side is being resized so as to constrain proportions). When you render it out, it looks like the height is being rendered at its original size, but the width is still maxing out at 1024 - the maximum texture size in the render settings. Again, WHY this should happen, I don't know. But the fact you corrected it by changing those settings seems to bear this out. As does the fact that a smaller video size, within the bounds of the 1024 max, does not cause the same problems. Just my thoughts and observations on the matter, based on your evidence so far... but I look forward to seeing any further developments. removes his dererstalker, and stops chewing the pipe stem friendlyrogue