Switching Facilities in MPEG-2: Necessary But Not Sufficient
S. Merrill Weiss, consultant
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Content Summary
MPEG-2 provides hooks for "switching", i.e. realtime interpolation of different source content into a media stream, but the hooks provided are insufficient for the commercial requirements of cable and TV, especially compared to current analog systems. Problems include:
- Insufficiently tight bounds on stream parameters in MPEG-2 standard
- Effect of different transport stream data rates
- "Temporal lookahead" in heterogeneous encoded streams, resulting in unpredictable burstiness and buffering problems for statistical multiplexing
- Frequent need to do at least some amount of decoding and recoding in order to disassemble and splice streams in real time
The author proposes standardized data and packet rates (integral multiples of things), standardized program element lengths (doesnąt TV already have this?), standardized entry points for streams with guaranteed bounds on buffer conditions at those points, and building transitions into pre-encoded material (yeah, right).
Relevance to Multimedia
MPEG-2 is the anointed HDTV format, and although it provides the mechanism for doing stream switching, it lacks sorely needed policy to make switching really feasible.
Rating
2 out of 5: A good point, but this paper should have been no more than 5 pages long.
Armando Fox (fox@cs.berkeley.edu)