Who uses constrained parameters bitstreams?
A. Principal CPB applications are Compact Disc video (White Book or CD-I) and desktop video. Set-top TV decoders fall into a higher sampling rate category known as “CCIR 601” or “Broadcast rate,” which as a rule of thumb, has sampling dimensions and bandwidth 4 times that of SIF (Constrained Parameter sample rate limit). Are there ways of circumventing constrained parameters bitstreams for SIF class applications and decoders ? A. Yes, some. Remember that CPB limits pictures by macroblock count (or pixels/frame). 416 x 240 x 24 Hz sampling rates are still within these constraints. Deviating from 352 samples/line could throw off many decoder implementations which possess limited horizontal sample rate conversion abilities. Some decoders do in fact include a few rate conversion modes, with a filter usually implemented via binary taps (shifts and adds). Likewise, the target sample rates are usually limited or ratios (e.g. 640, 540, 480 pixels/line, etc.). Future MPEG decoders will likely i
