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Marking Time
Marking Time
However accurate quartz system clocks are, they do remain individual and separate. This means that the
precise duration of a second varies between them. The difference will be very small, but over a day,
fractions of a second either way accumulate, and at 60 fps, drift between system elements can become
apparent. This guide provides a basic overview to how the elements in a Delta Media Server show
system can be synchronised, and when and why this matters.
DeltaServer synchronises frame display with the refresh clock of the server's output GPU(s). The first
pixel is presented at the very start of the first line, every time. But when we have a number of servers,
or multiple GPUs in each, many display devices, audio, and other parts of the system, show controllers
and so on, how do we keep everything perfectly in sync?
Time, and Displaying Frames (Refresh)
Multiple graphical displays shared across several servers on the same display system will not be
synchronous unless the graphical processing units (GPUs) in all servers themselves are fully
synchronised. Display hardware must synchronise the screen refresh across all display devices, by using
a common, repeating timing pulse to trigger the VSync signal in every display and synchronise the
HSync. Absolute or elapsed time does not matter: but each new frame will be displayed simultaneously
across all devices. A genlock input per server, and a simple house-sync pulse generator is all that is
required for display synchronisation.
Matching Frame Delivery and Display
When frames are passed from DeltaServer to a graphics processor (GPU), the frame will be held until the
VSync signal is ready. When in 'Auto' or 'Hardware Timed' mode, DeltaServer is locked to the GPU
refresh clock, whether this is internal to the GPU, or drawn from an external sync reference. Frames
must therefore be completely loaded before the VSync, otherwise a frame may be dropped. Delta pre-
caches a configurable number of frames from disk to ensure this does not happen. Presenting frames
from disk through to display requires adequate disk performance, graphics performance and processing
capacity, so the higher the media resolution, and the more blending, warping or effects being applied,
the more will be demanded from the server.
Movie Time
Sequential movies are always in frames, so the framerate is defined in its format. Delta allows the
application of framerate compensation, so that media of different framerates can be played on the
same timeline. This can be smoothed by choosing interpolation.
Synchroni s i ng Del ta Medi a Sys tems
© 2018 7thSens e Des i gn
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