In some embodiments, a server system composites in real-time, in response to a user video search query, a standard-compliant (e.g. MPEG-4/H.264) SD or HD video stream encoding a rectangular (x-y) composite video preview panel array (grid) of video search results. Each panel/tile in the rectangular panel array displays a temporal section (e.g. the first 90 seconds, looped-back) of a video identified in response to the user query. Generating the composite video panel array in real-time is achieved by compositing the component video panels in the compressed domain, after each panel undergoes a compressed-domain pre-compositing preparation process that facilitates dynamic compositing of the panels into a single video stream. The pre-compositing preparation includes transcoding to a format having a down-scaled common resolution, common GOP structure, and one-slice-per-row slice structure.