Betacam SX

The Betacam SX is a format digital video on tape 1/2 inch marketed by Sony in 1996 and intended to replace the analogical format Betacam SP (1986). It does not present any technological advance compared to the numerical Betacam (1993) of which it is before a a whole less expensive alternative.

It preserves the structure 4:2: 2 of the signal Video and implements a algorithm of reduction of flow based on the MPEG-2 422. It is the only numerical format which exploits the temporal redundancy between the images, by groups of two (images I and B). The effectiveness of compression being thus increased compared to an algorithm “all will intra”, the factor of reduction of flow could be high to 10: 1. The precision of assembly to the Image close however is ensured by a complex system ensuring the conversion of a bidirectional image B into an image mono directional P (ahead or behind), with each time necessary to the points of edition.

The video flow is of 18 Mbits/s, but the recorded total flow reached 40 Mbits/s. Betacam SX is a format says “not alignment”, because deprived of any circuit of dynamic follow-up of tracks: two heads shifted on the drum create a sufficiently broad beam of reading to cover all the traversed track, even when this one is not perfectly rectilinear. This clever process makes it possible moreover to ensure a reading at variable on a beach -1/+1 while being put up with the phase shifts of relative slope of the tracks.

Betacam SX treats 4 audio tracks 48 kHz/16 bits and is compatible in reading with the cassettes Betacam/Betacam SP. The durations of recording in SX are typically twice higher than in analogical Betacam, the band ravelling twice less quickly.

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