USB Video Capture frame rate drop after Standby/Wake-up cycle

Our USB Video Capture device running on XP on USB 2.0 runs
at 30 fps. However, if we put the system into Standby mode while
capturing a video (either capturing to file or simple video preview)
then when the system awakes the video capture resumes but at a
frame rate which now fluctuates around 24fps and goes as low as as
22 fps. It is visibly slower - not just a quirk in frame-rate reporting.

This reduction in frame rate is not cumulative. i.e. if we repeatedly
go into Standby mode and reawaken it remains at around 24fps.

The framerate can be is restored to 30fps by simply stopping and
restarting the video capture application.

The problem does not occur if we attach our device on a USB 1.1
port; the framerate then remains constant through Standby/Wake-up
cycles.

We have tried to test this on other vendor's USB video capture
devices to determine if it is a problem in our drivers but to date
have not yet found one that can survive running an application
through a Standby/Wake-up cycle without other, far more serious
problems.

Any assistance, or redirection to a more appropriate forum would
be appreciated.

Steve Thorpe

Max
Fri May 27 12:02:31 CDT 2005

I don't have the answer for you, but...

Does it happen only on one particular machine or did you try more than one
machine? Have you tried a different video card?

Are you sure that you USB hardward is happy after Standby and still can
stream out 30 fps? Can you run an experiment by disabling output in your
driver and NOT send anything out? Instead just measure what fps you are
getting internally from your device.

-- Max.



"Steve Thorpe" <empiasteve@online.nospam> wrote in message
news:ePY5mtjYFHA.3220@TK2MSFTNGP14.phx.gbl...
>
> Our USB Video Capture device running on XP on USB 2.0 runs
> at 30 fps. However, if we put the system into Standby mode while
> capturing a video (either capturing to file or simple video preview)
> then when the system awakes the video capture resumes but at a
> frame rate which now fluctuates around 24fps and goes as low as as
> 22 fps. It is visibly slower - not just a quirk in frame-rate reporting.
>
> This reduction in frame rate is not cumulative. i.e. if we repeatedly
> go into Standby mode and reawaken it remains at around 24fps.
>
> The framerate can be is restored to 30fps by simply stopping and
> restarting the video capture application.
>
> The problem does not occur if we attach our device on a USB 1.1
> port; the framerate then remains constant through Standby/Wake-up
> cycles.
>
> We have tried to test this on other vendor's USB video capture
> devices to determine if it is a problem in our drivers but to date
> have not yet found one that can survive running an application
> through a Standby/Wake-up cycle without other, far more serious
> problems.
>
> Any assistance, or redirection to a more appropriate forum would
> be appreciated.
>
> Steve Thorpe
>
>
>