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Osprey 240e/450e User Guide
ViewCast 29
You can set start lines all the way up to 27/290. (On the PCI products which have a Direct Mode option,
PostProcessing Mode must be set in order to have top lines below 23/286.)
When the start lines are below 23/286, the bottom of the video frame spills off the bottom of the 485-
line NTSC-standard frame. In this case, the driver adds black lines at the bottom of the frame.
Note: If you select start line 21/284, Closed Captions cannot be decoded.
Changes to this control take effect as soon as you click Apply or OK.
Source Width
Figure 28. Source Width
The Source Width control (Figure 28) works in conjunction with the Horizontal Delay control to adjust
the width and borders of the active video field.
The Source Width control adjusts the width of the portion of the video line that is captured. Another
way to understand it is that it moves the right edge of the video horizontally in the capture or preview
frame. (This control does not move the left edge – the left edge is affected only by the Horizontal Delay
control.) The minus button moves the right edge to the left, the plus button moves it to the right.
Adjustments are relative to the standard CCIR horizontal size of 720 pixels. The [720] button resets the
width to that default. The [704] button sets the width to a useful smaller size. The range of adjustment is
from 688 to 720.
The recommended procedure is to perform this adjustment in conjunction with the Horizontal Delay
adjustment, as follows:
1. Do the adjustment with a live preview stream running, so you can see changes immediately.
2. First use the Horizontal Delay adjustment to set the left edge of the video.
3. Then, use the Source Width adjustment to set the right edge of the video.
It is possible to obtain the same result using the cropping control (Size and Crop Tab) but there are some
differences.
The Source Width control affects all pins and all filters on the device, whereas the crop
control must be set separately for all SimulStream filters.
In Post-Processing Mode, this operation is often more efficient in terms of processing than a
crop operation. The crop and scale are done in hardware, so if you are using the resultant
640 x 480 image directly without further cropping there is no scale/crop processing cost
incurred.