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As we said above, really a little video latency is not a bad thing as viewed from a surprisingly short
distance back into the audience. This is just as well, since for all practical purposes a little latency is also
unavoidable.
Even so, as long as audio and video are in sync
at your seat
, only a rather ‘significant’ degree of latency
will be objectionable – unless you happen to be very near the stage. For those in the front rows, a few
extra frames of latency
may
be rather disconcerting. (It’s true that IMAG was conceived primarily for the
benefit of those further back, but if the latency is too obvious for those nearest the front it can be
disconcerting distraction.)
For this reason, it’s desirable to keep video latency to an agreeable minimum – but put away any notion
of ‘zero latency.’ Not only would this require bending the laws of physics, it would be a bad idea.
Even before considering minimizing latency in the device chain, acknowledging that there is always going
to be some latency calls for some creative thinking with regard to practical staging. For example, if you
design your IMAG layout in such a fashion that those in the front row are unlikely to be able to see the
screen(s) without lifting their eyes from the onstage talent, they are extremely unlikely to notice a small
amount of latency.
Latency and Your AV-HLC100
Your AV-HLC100 live production system constitutes just one (albeit critical) link in a chain of devices. It
is common for each device to contribute a little to the combined total latency for the system.
AV-HLC100’s portion of the total latency sum is well within acceptable standards for devices of this sort
– roughly between 1 and 2.5 frames (the actual amount can vary slightly within this range, depending on
several factors).
For example, suppose a ‘video frame’ supplied by a camera arrives at an input one millisecond after a
different frame has been sent to the output. Obviously the new arrival must wait its turn; it can’t be
transmitted until the correct duration for its predecessor has elapsed. Thus the newly arrived frame
must ‘wait’ almost one entire frame, until its turn comes.
You can actually perform a rough assessment of the latency of your pipeline fairly easily. Run timecode
directly to 1) a monitor and at the same time 2) through the switcher to a second (identical) monitor. Take
a photograph that encompasses both monitors, and compare the timecode shown.
Other Sources of Latency
More often than not, significant latency is added by other devices in the IMAG chain that come
after
the
switcher. Projectors are a common contributor, but cameras are often a factor, too.
Here are some helpful points to consider when designing and connecting your system:
•
If at all possible, match the resolution sent from the switcher to the native resolution of the
projector. (On some projectors this allows the unit to avoid using its own internal scaling, which is
often a significant factor in unwanted latency.)
•
Certain projectors provide a ‘low latency mode’ to disable features of the unit that carry a heavy
toll in latency. Enabling this mode can make positioning the projector slightly more challenging
