70
Osprey-300 User’s Guide
On the other hand, if overlay video is
sized to 160x120 because that is the
DirectShow default setting, and the
capture video is sized by VidCap32 to
640x480, then overlay will be captured at
160x120 and scaled up 1:4 in software to
the 640x480 size of the VidCap32 overlay
window – resulting in a very grainy image
with 4x4 cells.
• With VidCap32, video capture runs all
the time, even when no video is being
previewed or captured. The reason is
perhaps so that the mapper can support
Video for Windows “preview”, which is
derived from the DirectShow capture
stream.
• A Video for Windows application running
over a DirectShow driver may consume 25
to 50 percent of system bandwidth even
when it is doing nothing.
• If you are going to extensively use a
Video for Windows application with a
DirectShow driver, make sure that the
DirectShow preview pin’s default size is
correctly set. As explained, you have to
use a native DirectShow application to do
this. Open the driver’s filter dialog, go to
the Crop tab, and set Default Size there.
Most often, you would want to set the
preview pin to the capture size you plan to
use. But if you aren’t going to use Video
for Windows overlay, or are not concerned
about its quality, then set the preview pin
to a very small size such as 160x120.
D
E
-I
NTERLACING
Most video is provided for viewing in an
interlaced format. For simplicity, NTSC is used
in the following explanation of an interlaced
format. NTSC video is basically composed of
images taken 60 times a second. Each image is
called a field, and there are odd and even fields.
While these odd and even fields are temporarily
adjacent to each other in time, the horizontal
lines that make up these fields are spatially
different.
Содержание Osprey-300
Страница 1: ...Osprey 300 User s Guide...
