Nevion FRS-HD-CHO - Manual (Page 20)

FRS-HD-CHO Rev. 9
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Figure 12: Negative phase delay
The phase delay can thus be written in several ways, a large positive delay will equal a small
negative delay, because there is wrap-around on a frame basis. It follows that it is not useful
to specify a phase delay larger than 1 frame. Strictly speaking the range could have been
limited to -1/2 frame to 1/2 frame. For convenience, the delay range is allowed to be from -1
frame + 1100 samples to 1 frame
– 1100 samples.
In order for FRS-HD-DMUX to honor the phase delay setting, it should ideally delay the
incoming video between 0 to 1 frames. Because the processing delay through the card is 2
lines minimum, the actual window is between 2 lines and 1 frame + 2 lines. Hence, with the
parameter (minimum) video delay set to 2 lines (the least number possible for the
parameter); the output video will be between 2 lines and 1 frame + 2 lines delayed, with
respect to the incoming video. A common occurrence in practical use is to synchronize an
incoming video with a sync, but to let the outgoing video lead some samples or lines to the
sync. This can easily be accomplished. Say that we want the outgoing video to occur 50
samples before the sync. We will then set the phase delay to -50 samples, and the video
delay parameter to 2 lines. For convenience, let us assume that the incoming video is iso-
synchronous, but that it lags 20 lines after the sync. We will then have the situation shown in
Figure 13.
Note that the numbers in circles in the next figures are visualizing the video frames.