One system described herein, among others, comprises receiving a plurality of slice groups created by converting a plurality of video stream using flexible macroblock ordering (FMO); compositing a plurality of slice groups to create a sequence of composite pictures, wherein the sequential progression of compositing pictures from the source video streams is according to pictures having a presentation time within a time interval corresponding to the composition operation; adding pad slice groups to the source slice groups to create a composite image compatible with a video standard, wherein the pad slice groups are added to create a rectangular composite picture size compatible with an output display format, and wherein the pad slice groups are keyed with a distinct pattern indicative of padding for the composite pictures; and transmitting a single composite output stream comprised of reordered source slice groups and pad slice groups.