Failed to get the video monitor interface object

[Albert Pinto]

Hi,

I am writing an application(using the directshow apis) to capture the
images from a analog device. I am successfully able to catpure the
image.

Our requirement is to capture the image as soon as there is hardware
trigger on the device. For this requirement solution I found we can
set SetMode to VideoControlFlag_ExternalTriggerEnable via
IAMVideoControl interface.

As per MSDN VideoControlFlag_ExternalTriggerEnable : Sets up a stream
to capture a trigger from an external source, for example, a push
button on a camera. Buffers can be queued to the driver but will not
be passed up from the WDM capture driver (for compression, display, or
writing to a file) until the external event happens.

The problem here is on querying the IAMVideoControl I get the
E_NOINTERFACE error.

Please let me know what is right way to do the same or if there is any
other way I can set the device to ExternalTrigger mode?

Also is there any way to disable interlacing? since some time while
capturing the images we get the interlaced images.

Any help in this regard is highly appreciated.

Thanks in advance.

Best Regards
Alber

[Alessandro Angeli]

From: "Albert Pinto"

> As per MSDN VideoControlFlag_ExternalTriggerEnable : Sets
> up a stream to capture a trigger from an external source,
> for example, a push button on a camera. Buffers can be
> queued to the driver but will not be passed up from the
> WDM capture driver (for compression, display, or writing
> to a file) until the external event happens.
>
> The problem here is on querying the IAMVideoControl I get
> the E_NOINTERFACE error.
>
> Please let me know what is right way to do the same or if
> there is any other way I can set the device to
> ExternalTrigger mode?

The docs also say that <<<For Windows Driver Model (WDM)
devices, the WDM Video Capture Filter automatically exposes
this interface if the WDM driver supports the
PROPSETID_VIDCAP_VIDEOCONTROL property set.>>> or, in other
words, support for this interface is optional.

> Also is there any way to disable interlacing? since some
> time while capturing the images we get the interlaced
> images.

I already replied in your previous thread, do not keep
asking the same question in different threads.

--
// Alessandro Angeli
// MVP :: DirectShow / MediaFoundation
// mvpnews at riseoftheants dot com
// http://www.riseoftheants.com/mmx/faq.htm