Grass Valley Switcher Products - Manual (Page 12)

12 Switcher Products — Protocols Manual
Section 1 — Tally Protocol
Iso Tally
Iso tally indicates which sources contribute to a specific point in the
switcher video path whether or not those sources contribute to the program
output. For example, an ME iso tally indicates what sources contribute to
one or more of an ME’s program outputs. Iso tally is similar to output tally
except that the tally calculation is specified in terms of the ME outputs not
on physical outputs of the switcher. In fact, the ME outputs do not have to
be mapped to physical outputs in order to generate ME Iso tally.
Selection Tally
Selection tally indicates what source is selected on a particular bus or buses.
Selection tally does not follow reentries or factor in bus visibility. The buses
need not be on air for the sources to contribute to this information.
Selection tally requires specifying which buses of the switcher should be
included in the tally calculation.
Tally Calculation Basics
Tally status provides information about switcher sources based on the
video composite at some point in the video path. This section describes the
mechanisms used within the switcher to calculate tally relay closures. The
information is also useful when interpreting the “contribution tally” data
described later.
Many sources may be combined at each ME of the switcher and ME banks
can be reentered. In order to calculate tally status, the video and key paths
must be traced backwards from the video output through all MEs, keyers
and external processing equipment (e.g., a DVE) to the primary sources.
At each stage in the video path, tally calculations must take into consider-
ation whether or not a particular bus contributes to the composite and what
source is selected on the bus. If the selection is a primary source, the end of
that branch has been found. However, if the selection is a reentry (either
another ME or internal (e.g., frame store) or external processing (DVE), the
trace must continue in order to find sources which contribute to that pro-
cessing block’s output.
Calculations must include both video and key paths through the switcher.
Keyer Modifications
Keyers modify the video and key signals and affect tally calculations.
The keyer can either use the incoming video or replace it with a matte. In
addition, the key signal can be derived either from the incoming video,