[IOXperts Video-Developers] Re: OK, now how about ->two<- QuickCams?

[Steve Sisak]

At 6:06 PM -0700 1/9/04, rob shaw wrote:
>I was able to get a second "instance", and change which camera the 
>sequence grabber was looking at by using 
>SGSetVideoDigitizerComponent().  However, when I tried to just run a 
>parallel window in the minimung example, opening a second gworld, 
>etc. things were error-free until the last step, SGStartRecord() on 
>the second instance, when I got error -6981, "not enough bandwidth". 
>This makes some sense, as we're pushing the USB bandwidth, but I'd 
>be happy to get half the frame rate in each window.

Most modern Macs have multiple busses -- you should be able to put 
the cameras on different busses and operate both at full speed.

Also, if you look at our property API, you can set the bandwidth 
property of each video digitizer instance to <= 0x8000 to force that 
camera to use <= half of the available bandwidth on the bus. This may 
slow frame rate, increase image compression or reduce image size, but 
each camera will use only half of the bus.

BTW-Make sure you pay attention to the imate size in the 
ImageDescription returned by VDGetImageDescription (I think it may 
also be passed to you in the callback setup code) -- the driver may 
return a smaller image if there isn't enough bandwidth to give you 
the size you asked for -- note that a decompression sequence will 
just do the "right thing" -- you may also want to stop and restart 
the SG after changing the bandwidth property.

HTH,

-Steve
-- 
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Steve Sisak, CTO                                 steve.sisak at ioxperts.com
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