The GY-HM100 always records in HD which is 16:9 aspect ratio.  The camera provides a downconverted output via the A/V connector and break-out cable.  This signal can be in either the 16:9 or 4:3 (letterbox) mode depending on the menu selection.  A downconverted signal is also available through the component (Y, Pb, Pr) connector.  These signals are available while recording with the camera, or when playing back recorded video.