Letterboxing is the practice of transferring film shot in a widescreen aspect ratio to standard-width video formats while preserving the film's original aspect ratio. What exactly is the LBX aspect ratio setting for? Sometimes I watch 4:3 material that is letterboxed; that is, it has black bars on top and on the. WUXGA projection with 3400 lumens and 20000:1 contrast ratio; Extensive I/O support with 2xHDMI (with MHL), VGA-in, composite, audio-in, audio-out, USB. Dunno what LBX is but I do know that 16:9 is widescreen. LBX: This format is for non-16x9, letterbox source and for users. Letterbox (often abbreviated to LBX) means the video is presented in its theatrical aspect ratio, which is wider than standard or widescreen TV.