An enhanced screen codec for live lecture broadcasting

In this paper, we present the design of SJSC, an enhanced screen codec proposed by us for live lecture broadcasting. Compared to other screen codecs available, SJSC is more suitable for live broadcasting of a lecture on an unreliable transport medium like the Internet due to two features. First, an error-resilience mechanism controls the impact introduced by packet loss onto the decoded screen sequence. Second a unique frame-rate self-adaptation mechanism ensures the bit rate of the encoded stream is capped at a level that the underlying transport can sustainably support. SJSC has been successfully deployed in our p2p streaming based live lecture broadcast system, named PPClass, which has been put into real use in our college for more than 6 months and served 300+ classes for an accumulated 9000+ remote student base. Both subject assessment by real students and objective evaluation experiments have proved the effectiveness of its design.