ViewCast 450E, 240E manual No-Video Test Pattern, Buffers Requested

	Osprey 240e/450e User Guide
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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, solid blue, and solid black. The 75 % color bars are calibrated to show correct luma and chroma test patterns on a vector scope. The calibrations are slightly different for NTSC, NTSC-J, and PAL/SECAM.

You can also display a PNG or 24-bit BMP image when no video signal is present. The image will be stretched or shrunk to fit the size of the full video reference frame. If you are cropping the video, the crop is applied to the no-video image as well as to the video. The Select Image button displays a standard Windows file select sub-dialog to select the image. It is customary for BMP files to have a filename extension .bmp and for PNG files to have the extension .png. However, the driver determines the file type by reading the file header.

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 appear. Otherwise, whatever you enter, up to 32 characters displays on the test pattern.

If you select Show board info, the text display includes the device name, the currently selected video input, the PCI Express bus and slot number, and the board serial number. This display is useful for determining which physical board in the system corresponds to each device name.

Click Show board ID info to display the board serial number.

Buffers Requested

The driver tells DirectShow the minimum number of video capture buffers it needs to have allocated for proper operation (Figure 39). The client application may ask for a different number of buffers; in general DirectShow honors the larger of the requests.

Figure 39. 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.

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