Just passing through. Some video editing utilities pad the video clip with additional "junk", so even if you're using no compression (or lossless compression) and haven't altered the clip, there may be a file-size discrepancy between two otherwise identical videos. My editor-of-choice, VirtualDub, does the opposite; it strips the useless junk out of the video instead, and I typically end up with smaller file-sizes, even on a direct-stream copy with no recompression.