Re: [python-win32] Using DirectShow API to access webcam

[Tim Roberts]

Joe wrote:

using the DirectShow API, but could not get anything to work.

The question is already posted on StackOverflow:

I have a question an hope you can help me. I am trying to control a UVC webcam https://stackoverflow.com/questions/51843523/accessing-webcam-via-directshow-using-com-with-python

got my nowhere:

# IID_IAMVideoProcAmp is C6E13360-30AC-11d0-A18C-00A0C9118956
from win32com.client import Dispatch


iid = '{c6e13360-30ac-11d0-a18c-00a0c9118956}'

print(GetClassForCLSID(iid))
print(GetModuleForProgID(iid))
print(GetModuleForCLSID(iid))

CLSID = IID('{c6e13360-30ac-11d0-a18c-00a0c9118956}')
print(CLSID)

print(Dispatch(CLSID))

I am not familiar with using CLSID, IID so playing with the few examples I found from win32com.client.gencache import EnsureDispatch,GetClassForProgID, GetClassForCLSID, GetModuleForProgID, GetModuleForCLSID

pywintypes.com_error: (-2147220990, 'CONNECT_E_CANNOTCONNECT', None, None)

Could someone of you point me in the right direction and maybe put
together a few lines to get me started?

    https://gist.github.com/dust8/3890196



Alternatively, it looks like this package might be more applicable:

    http://videocapture.sourceforge.net/

--
Tim Roberts, t...@probo.com
Providenza & Boekelheide, Inc.

I am not entirely convinced it is possible to control DirectShow from Python, but I'll give you some general information. An "interface" in COM terms, described by an IID, is just a set of functions declarations.  It defines the things you can do with an object, but it is not actually an object.  A "CLSID", on the other hand, defines a COM object.  The CLSID doesn't tell you what the object can do, it's just a way of creating an object.  Once you have used a CLSID to create an object, you can ask it for an interface. So, you can't just create IID_IAMVideoProcAmp.  You have to ask an existing object for its IAMVideoProcAmp interface.  You would create your camera object, and then query the camera object for IAMVideoProcAmp. Creating a DirectShow graph is a multi-step process.  You create a filter graph, you add your camera to the graph, you tell the graph to render the stream (which means it automatically fills in the other filters), and you control it.  Here is some sample code that does this: This is actually more complicated than it needs to be, because it's trying to handle TV devices with tuner and audio filters as well. You don't need that.  Once you have a device from VideoInputDeviceCategory, you don't need the video decoder or the audio.  You can just render the graph at that point.

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