ViewCast Osprey-450e - Manual (Page 45)

Osprey 240e/450e User Guide
ViewCast 39
Apply Click Apply to apply the settings.
Help Click Help to access the user guide.
No-Video Test Pattern
You can select one of four patterns to appear when no video signal is present – 75% color bars,
100% color bars, blue, and black.
You can place a text line on the test pattern. If the Text edit box is empty - no spaces and no text
characters – then no text will exist. Otherwise, whatever you type here, up to 32 characters, displays
on the test pattern.
Click Show board ID info to display the board serial number.
Buffers Requested
The driver can tell DirectShow the minimum number of video capture buffers it needs to have
allocated for proper operation (Figure 34). The client application may ask for a different number of
buffers; in general DirectShow honors the larger of the requests.
Figure 34. Number of Capture Buffers Requested
Buffers are used in a round-robin style. The driver fills a buffer; the client then consumes the buffer,
and releases it when it is done. The buffer then circulates to the driver to be filled with video again.
If the client holds on to a large number of buffers at once, there may be no empty buffers available
to the driver and frames may be dropped. The solution is to allocate a larger number of buffers.
Capture and encoding applications generally need a large number of buffers so they can deeply
pipeline the downstream processing without danger of buffer starvation at the driver. If buffer
starvation is evident, in the form of dropped frames, you can try increasing the number of buffers
allocated for the Capture pin.
Preview video that is directly rendered on the screen does not use deep pipelining and cannot
benefit from it. There has been some evidence that too many buffers for direct rendering can harm
performance.
In that case, on the Capture pin, increase the number of buffers from the default 100 for deeper
pipelining and more resistance to dropped frames.
On the Capture pin, you can reduce the number of buffers to around 5 if the video is going to be
used only for direct rendering. Remember to put the number back to 100 or more for capture or
encoding – 5 may not be enough and may result in many dropped frames.
On the Preview pin, you can increase the number of buffers to 20 or more if you are using it for
capture or encoding rather than direct rendering.