Miranda NV5100MC Master Control, Справочное руководство

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168 Rev 2.10 • 17 Feb 11
A. Special Features
Machine Control and Pre-Roll
The pre-roll period is essentially the longest pre-roll value of the pending sources.
Theory
The pre-roll period is calculated in relation to the point at which new video appears on the program
bus. In a V-fade, for example, that is in the middle of the transition. (See Figure A-2, following.)
MasterConfig refers to the cue point. The cue point can be configured to be the mark point or at the
pre-roll point :
• Pre-roll point.
The panel operator will position a tape and press the mark button. The tape is then at the MCE’s
“mark” point. If the operator then presses the cue button, the VTR will reposition the tape in
advance of the mark point by the number of frames specified as the pre-roll value.
• Mark point.
The panel operator will position a tape and press the mark button. The tape is then at the MCE’s
“mark” point. The cue button also positions the tape at this point. (Pre-roll positioning must be
performed using some other means.)
Most cases use the pre-roll point, where:
For each sources, cue = mark – pre-roll.
The actual timing of the transition is further adjusted by a device latency value:
Effective pre-roll = max [ all (pre-roll + latency) ]
Transition pre-roll = max [ effective pre-roll, system pre-roll ]
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The VTR gets “parked” at the pre-roll point. It is only when transition timing is calculated or
when the transition executes that latency matters.
It is in the DC21 configuration that the “device latency” is specified. That latency is essentially a
“fudge factor” that you must determine experimentally.
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Device latency depends in part on the time it takes for commands to get from the MCE through
the DC21 to the device. Good pre-roll values must also be determined by experimentation.
About Preroll and Latency
A source configured with pre-roll will always have the defined preroll when it participates in a tran-
sition. However, if a source is configured for serial machine control, then that source’s
effective
pre-roll may be longer. The device controller has a “Device Internal Latency” field in its device
configuration table (accessed through the ‘Protocol Assignment’ page). The “device internal
latency is intended to account for all delays in the serially controlled device (such as mechanical
ballistics and serial command pipeline delay) that effectively lengthen the pre-roll.
For example, a serially controlled VTR configured for a 3-second pre-roll might typically have a
device internal latency setting of between 5 and 8 frames, to time the first frame of video with the
point at which new video must appear as part of the master control transition.
If this single source were the only machine-controlled source involved in the transition then the
“effective pre-roll” for this transition would be 3:08 (3 seconds and 8 frames).
When several sources having machine control are involved in a transition, the transition’s effective
preroll is the longest of any of the sources’ effective preroll.
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Please note that a source can be configured to have pre-roll without having machine control.
Such a source’s contribution to a transition’s effective pre-roll still holds, but without the contri-