Using Multpiple Interleaved Time Bases in Hypermedia Synchronization

This paper discusses how multimedia languages and players can handle multiple time bases in supporting inter-media synchronization with interleaved media contents transmitted as unsolicited streams (pushed data). More specifically, we are interested in inter-media synchronization defined by causal/constraint relationships. Unsolicited interleaved media-contents are usual in digital TV systems, in particular in broadcast TV, in which adverts are inserted into programs transmitted sequentially. Although some existing middleware systems address the problem, their solutions have limitations. This work proposes an alternative approach providing high-level abstractions that hide or minimize the complexity of dealing with interleaved media-content as part of hypermedia applications. The proposal has been incorporated in the Nested Context Language (NCL) and in its player, the main component of the Ginga digital TV middleware. However, despite using NCL as an example, the proposal has a broader spectrum and can be adapted and used in other languages and respective engines.