SWITCHING FACILITIES IN MPEG-2 - NECESSARY BUT NOT SUFFICIENT

MPEG-2 provides a number of facilities intended to permit the time con catenation of separately compressed program segments through the assem ble and insert editing of those segments downstream front their encodi ng or release points, Such facilities are necessary to support some of the mechanical aspects of switching between segments in the assembly of programs and other continuity elements for release and in the downs tream insertion of commercials. But the switching hooks provided in MP EG-2 transport stream packetization, however necessary they may be, ar e not sufficient to the task. Several operational steps must be taken for continuity integration to succeed in producing a smoothly flowing output without the appearance of a ''channel change'' at the switching points, Indeed, for the successful integration of material encoded at different locations, these operational steps must be precisely define d and standardized. This paper examines the supporting functions provi ded by MPEG-2 and will suggest a number of areas in which agreement mu st be reached on operations practices before successful networks can b e built.