By Mukta Kar, Ph.D., Majid Chelehmal, Ph.D., Richard S. Prodan, Ph.D., Cable Television Laboratories
Current advertising insertion systems enable cable headends and broadcast affiliates to insert locally-generated commercials and short programs in a remotely distributed regional program before delivery to the home viewer. The revenue generated by the local ads and short programs is very significant. Current ad insertion systems are analog in nature, switch between uncompressed video sources, and use digital video compression for local storage only. Digital compression provides digital audio, video, and data with superior quality and efficiency to existing analog means. The application considered in this paper involves insertion of locallygenerated compressed digital commercials and short programs into a digital channel containing previously multiplexed and digitally compressed programs. However, combining compressed video streams presents additional challenges for seamless insertion of ancillary programs. It is difficult to splice a compressed digital bitstream compliant to the MPEG-2 standard without adversely affecting the resultant display due to decoding failures at compressed bitstream discontinuities. This paper presents a brief overview of existing analog and digital program insertion systems.Various solutions, including limitations not present in current analog systems, are discussed. Flexibility, implementation complexity, and network operational constraints are also discussed for various potential digital program insertion methods.