Movie files created by professional video applications frequently include an aperture mode setting. The aperture mode setting describes the pixel aspect ratio used during capture and controls the elimination of edge artifacts from the video frame. Depending on the aperture mode, the portion of the image area shown during playback will vary. The "Conform aperture to" option in QuickTime 7 Pro allows you to change the display of QuickTime movies that were created with an aperture mode setting.
More from Apple OS X Support ...