Re: Createfile

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From: Max Paklin (mpaklin_at_hotmail.com)
Date: 01/14/05 

Date: Fri, 14 Jan 2005 01:35:42 -0800

Wow, I didn't know they had a architecture for still frame aquisition in
usbcamd.
Anyways, I can't really tell you what to do as I've never done this myself.
However what you read in DDK does seem to make sense.

See my comments inline.

"Zhuang" <ZHuang@cogentsystems.com> wrote in message
news:OgD%23oBR%23EHA.4072@TK2MSFTNGP10.phx.gbl...
> Sir:
> I read the flow section in DDK:
>
> 2.3.3 Using Bulk Pipes to Retrieve Still Frames from the Camera
>
> An STI USB minidriver can retrieve still frames from the camera using
> USBCAMD bulk services. The following steps outline how to retrieve still
> frames from cameras that use bulk pipes for still image transfer.
>
> 1.. Open the WDM video capture source filter associated with the camera.

As I said earlier refer to amcap sample on how to locate and create an
instance of the filter that you are interested in.

> 2.. Open the still pin on the filter handle obtained in step 1.

This is a sort of mystery to me.
How is one supposed to "open" a pin?
What I've done in the past to capture a still frame was the following. I
wrote a simple sink filter that was taking a command from the app (via
trivial COM interface) and upon reception of the command it was submitting a
sample upstream to the connected Still pin. On the Still pin I was making a
copy of the current frame and sending it out. Plain and simple. Worked fine.

> 3.. Send a ReadFile on that pin with maximum-sized buffer.

I've never use classic ReadFile on KS pins.
Just like I said above I used KS/DShow infrastucture to submit a buffer to
Still pin.

This model looks way overcomplicated and I wouldn't do it the way it is
described. Just too much trouble, but maybe I miss something.

Sorry for not being of much help.

-- Max.

> 4.. Set the stream state from Pause to Run.
>
> 5.. Get the interface pointer to PROPSETID_VIDCAP_VIDEOCONTROL property
>
> set.
> 6.. Set the KS_VideoControlFlag_Trigger flag associated with property ID
> KSPROPERTY_VIDEOCONTROL_MODE.
>
> 7.. Once the video control handler of the camera minidriver receives the
> trigger request, it should call USBCAMD_BulkReadWrite with a NULL buffer
> pointer.
>
> 8.. USBCAMD will dequeue a data SRB from the still pin and call the
> minidriver's CamNewVideoFrameEx entry point before it starts the bulk
> transfer. The camera minidriver can reduce the requested size of the bulk
> transfer if it determines the actual still frame is smaller than the
> maximum size allocated by DirectShow.
>
> 9.. Upon completion of the bulk transfer, USBCAMD will call the
> CamProcessRawVideoFrameEx entry point for further processing. Afterward,
> USBCAMD will finish the stream class read request on the still pin.
>
> A user application can cancel a requested bulk read or write by sending a
> CancelIO to the still pin. If there is a need to load tables to the camera
> through a bulk out pipe, the USBD driver can send a WriteFile to the still
> pin.
>
> Still data flow is intended for use in a pull model. A pull occurs when an
> application requests a still. Still data flow will also work in a push
> model where it functions as a pull. A push occurs when the user pushes the
> button on the camera, triggering the device event. USBCAMD will send a
> KSEVENTSETID_VIDCAPTOSTI event which can be propagated all the way to the
> imaging application.
>
> please tell me how to do?
>
>
>
>
> "Max Paklin" <mpaklin@hotmail.com> wrote in message
> news:OKp#1nH#EHA.3596@TK2MSFTNGP12.phx.gbl...
>> You don't normally use CreateFile for that. Check out AmCap sample from
>> DX
>> SDK (or old Platform SDK). It shows how to uses System Device Enumerator
> to
>> look up a device from a particular category.
>> Also you don't normally want to open pin by calling CreateFile. What you
>> usually do is to connect a pin to an input pin of another filter and
> process
>> data when it comes to that pin.
>>
>> -- Max.
>>
>>
>>
>> "Zhuang" <ZHuang@cogentsystems.com> wrote in message
>> news:uQrMfXF%23EHA.4004@tk2msftngp13.phx.gbl...
>> > How to use Createfile Function to Open the WDM video capture source
> filter
>> > associated with the camera?
>> > How to use Createfile Function to Open the still pin on the filter?
>> >
>> > rainwin Huang
>> >
>> >
>>
>>
>
>

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