Mboxtime - PRG MBOX User Manual

MboxTime

As noted in the previous section, layer sync between two Mbox servers is very good, but it is not perfect. It is possible
for the two servers to deliver a frame of video slightly out of sync due to delays in sync stream transmission over the
network or simply because the internal playback engines of the Mbox applications on the two separate computers are
not perfectly in sync. The results of imperfect sync are most noticeable when outputs from multiple servers are used in a
overlapped and blended projection system or for adjacent LED processors. The output from one server may be slightly
ahead or behind that from another, causing imagery to look as if there is a "tear" between outputs.
The Mbox application's playback and rendering engines run in lock-step with the internal processing "clock" of the
computer. But two different computers will always have very slightly different clocks. Without a common timing
reference, it is impossible to guarantee that two separate computers will deliver the same video frame at exactly the
same time. In order to get perfect playback sync between two Mbox servers, the two servers need to have a common
timing reference. When the Mbox application is receiving a timing reference, it can determine the host computer's clock
offset from the reference time, and apply its own offset to playback. Different computers may require slightly different
offsets.
Mbox v4 has a new feature called MboxTime. MboxTime encompasses the common timing reference and the
compensation that each instance of Mbox applies to its playback to be in sync with the common reference. The
MboxTime common timing reference can be received as either a timecode signal or as a network signal. The type of
signal to be used is selected in the Misc section of the Mbox application's Preferences tab.
IMPORTANT! MboxTime is not the same as network timecode from TC Reader or Mbox Remote or layer sync streams
from Mbox, but is intended to be used with some form of playback sync.
Guidelines:
+ All Mbox servers must receive the same MboxTime reference, whether it is timecode or network-based.
+ When MboxTime is used for perfect sync between servers, those servers MUST use a synchronization playmode -
layer sync or timecode sync, otherwise the MboxTime reference will be ignored since no attempt is being made to
sync playback.
+ When received as timecode, the reference must be received as SMPTE (audio) timecode directly into the Mbox
application.
-
The Mbox application must have its audio input preference configured to receive audio on an active interface,
this preference cannot be set to "None".
-
There can be only one source of the SMPTE signal for use as the timing reference.
-
For best results SMPTE used as the MboxTime reference should not start and stop or jump around. The Mbox
application is able to adjust for this, but when the reference is not running or when it jumps, the sync may not be
perfect. Therefore, it is not a good idea to use the same SMPTE as the MboxTime reference and for playback
sync, as timecode for playback sync often starts and stops or jumps around.
MBOX® USER MANUAL
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