letterboxing definition
letterboxing or “black padding”) that may fall outside of the active picture area of the original source content. The dimensions of the active picture area of a video track are specified by the width and height fields of the Track Header Box (‘tkhd’), as described in Section 2.3.5. These values are specified in square pixels, and track video data is normalized to these dimensions before any transformation or displacement caused by a composition system or adaptation to a particular physical display system. When sub-sampling is applied, as described above, the number of coded macroblocks is scaled in one or both dimensions. However, since the sub-sampled picture area may not always fall exactly on a macroblock boundary, additional AVC cropping parameters are used to further define the dimensions of the coded picture, as described in Section 4.3.4.
letterboxing means an activity similar to geocaching in which the participant takes directions and uses those directions to find a hidden object. The directions normally are in the form of a riddle, and the hidden object is a stamp that the participant uses to stamp a piece of paper to prove he has visited the site.