The Digital Fact Book - Quantel

VaporwareSoftware or hardware that is promised or talked about but is not yet completed – and maynever be released.See also: RSNVariable bit rate (VBR) compressionWhile many video compression schemes are ‘constant bit rate’ – designed to produce fixeddata rates irrespective of the complexity of the picture, VBR offers the possibility of fixinga constant picture quality by varying the bit-rate according to the needs of the picture.This allows the images that require little data, like still frames in MPEG-2, to use little dataand to use more for those that need it, to maintain quality. The result is an overall savingin storage, as on DVDs, better overall quality, or more efficient allocation of total availablebit-rate in a multi-channel broadcast multiplex.See also: Constant bit rate, DVD, Statistical multiplexingVaricamPanasonic camcorder based on DVCPRO HD that was the first to offer variable frame ratesfrom 4 to 60Hz at 1280 x 720P. So, if working at a nominal 24 fps, the system offers x 6 speedup (undercranking) to x 2.5 slow down (overcranking). The system works by continuouslyrecording 60 f/s to tape while the images are captured at the appropriate rate. Then therelevant useful frames are flagged. Editing equipment with a Varicam interface can usethe flag to record the right frames and so replay them at the right speed (e.g. PanasonicVTR AJ-HD1700 and Quantel editing systems).See also: VFRV173