UVC摄像头扩展单元功能的开发步骤是什么？

写在扩展单元的题外话

本人在开发支持UVC扩展单元的directShow应用时，必现并不需要注册接口，只需要在其源过滤器参照后续的代码枚举相关的接口如IKsControl，IKsTopologyInfo定位到指定的扩展单元接口后，直接使用其对应的IKsControl：：KsProperty即可实现扩展单元的特定类请求。

使用本站的UVC扩展单元调试工具进行调试：http://www.usbzh.com/article/detail-516.html

UVC扩展单元的固件支持

要进行UVC摄像头扩展单元的开发，首先第一是需要摄像头的描述符中含有UVC扩展单元描述符.

一个扩展单元描述符的示例：

BYTE  Length:            0x1a
BYTE  DescriptorType:    0x24
BYTE  DescriptorSubtype: 0x06
BYTE  bUnitID:           0x05
GUID  guidExtensionCode: xxxxxxxx-xxxx-xxxx-xxxxxxxxxxxxxxxx
BYTE  bNumControls:      0x03
BYTE  bNrInPins:         0x01
BYTE  baSourceID[0]:     0x01

说明：

• bUnitID：不能和别的ID冲突。
• guidExtensionCode：需要通过guidgen.exe生成一个惟一的ID标识。

其它要求：https://docs.microsoft.com/zh-cn/windows-hardware/drivers/stream/device-requirements-for-usb-video-class-extension-units

扩展单元的注册

扩展单元的注册可以使用INF文件进行注册，也可以吏用注册表进行注册，也可以使用DLL注册。

使用INF文件进行扩展单元注册

INF 文件可用于提供设备特定的名称或注册扩展插件单元。
详情可叁考：
https://docs.microsoft.com/zh-cn/windows-hardware/drivers/stream/providing-a-uvc-inf-file

使用注册表进行扩展单元进行注册：

HKLM
{
    NoRemove SYSTEM
    {
        NoRemove CurrentControlSet
        {
            NoRemove Control
            {
                NoRemove NodeInterfaces
                {
                    ForceRemove {xxxxxxxx-xxxx-xxxx-xxxx-
                       xxxxxxxxxxxx} = s 'Extension Unit
                       Property Set'
                    {
                        val IID = b 'yyyyyyyyyyyyyyyyyyy
                           yyyyyyyyyyyyy'
                        val CLSID = b 'zzzzzzzzzzzzzzzzz
                           zzzzzzzzzzzzzzz'
                    }
                }
            }
        }
    }
}

https://docs.microsoft.com/zh-cn/windows-hardware/drivers/stream/sample-registry-entry-for-uvc-extension-units
https://docs.microsoft.com/zh-cn/windows-hardware/drivers/stream/sample-extension-unit-plug-in-dll

使用插件DLL注册

使用DLL注册，需要先添加注册表项：

HKCR
{
    NoRemove CLSID
    {
         ForceRemove {zzzzzzzz-zzzz-zzzz-zzzz-zzzzzzzzzzzz} = s 'CompanyName Extension Unit Interface'
        {
            InprocServer32 = s '%MODULE%'
                                                {
                                val ThreadingModel = s 'Both'
                                                }
        }

    }
}

示例详见：https://docs.microsoft.com/zh-cn/windows-hardware/drivers/stream/sample-extension-unit-plug-in-dll

UVC 扩展单元的示例应用程序

pUnkOuter这个指针是UVC-CAMERA源，可通过下列函数指针ppSrcFilter返回。DeviceName是UVC设备名称。

HRESULT  CCamera::FindCaptureDevice(const std::wstring& DeviceName,IBaseFilter** ppSrcFilter)
{
    HRESULT hr;
    IBaseFilter* pSrc = NULL;
    IMoniker* pMoniker = NULL;
    ULONG cFetched;

    if (!ppSrcFilter)
        return E_POINTER;

    // Create the system device enumerator
    CComPtr <ICreateDevEnum> pDevEnum = NULL;

    hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC,
        IID_ICreateDevEnum, (void**)&pDevEnum);
    if (FAILED(hr))
    {
        printf("Couldn't create system enumerator!  hr=0x%x", hr);
        return hr;
    }

    // Create an enumerator for the video capture devices
    CComPtr <IEnumMoniker> pClassEnum = NULL;

    hr = pDevEnum->CreateClassEnumerator(CLSID_VideoInputDeviceCategory, &pClassEnum, 0);
    if (FAILED(hr))
    {
        printf("Couldn't create class enumerator!  hr=0x%x", hr);
        return hr;
    }

    // If there are no enumerators for the requested type, then 
    // CreateClassEnumerator will succeed, but pClassEnum will be NULL.
    if (pClassEnum == NULL)
    {
        MessageBox(NULL, TEXT("No video capture device was detected.\r\n\r\n")
            TEXT("This sample requires a video capture device, such as a USB WebCam,\r\n")
            TEXT("to be installed and working properly.  The sample will now close."),
            TEXT("No Video Capture Hardware"), MB_OK | MB_ICONINFORMATION);
        return E_FAIL;
    }

    // Use the first video capture device on the device list.
    // Note that if the Next() call succeeds but there are no monikers,
    // it will return S_FALSE (which is not a failure).  Therefore, we
    // check that the return code is S_OK instead of using SUCCEEDED() macro.

    while (S_OK == (pClassEnum->Next(1, &pMoniker, &cFetched)))
    {
        IPropertyBag* pPropBag;
        hr = pMoniker->BindToStorage(0, 0, IID_IPropertyBag, (void**)&pPropBag);
        if (SUCCEEDED(hr))
        {
            //获得Filter的Friendly Name
            VARIANT varName;
            VariantInit(&varName);
            hr = pPropBag->Read(L"FriendlyName", &varName, 0);
            if (SUCCEEDED(hr))
            {
               // TCHAR* pName = (TCHAR*)varName.bstrVal;
                std::wstring str(varName.bstrVal);
                if (str == DeviceName)
                {
                    hr = pMoniker->BindToObject(0, 0, IID_IBaseFilter, (void**)&pSrc);
                    if (FAILED(hr))
                    {
                        printf("Couldn't bind moniker to filter object!  hr=0x%x", hr);
                        return hr;
                    }
                    break;
                }
            }
            VariantClear(&varName);
            ////创建Filter实例
            //IBaseFilter* pFilater;
            //hr = pMoniker->BindToObject(NULL, NULL, IID_IBaseFilter, (void**)&pFilter);
            //pPropBag->Release();
        }
        pPropBag->Release();
        pMoniker->Release();
    }

    * ppSrcFilter = pSrc;

    return hr;
}

应用程序通过使用 IKsTopologyInfo::CreateNodeInstance ，然后调用节点对象上的 QueryInterface 以获取所需的 COM API 来访问接口。

// pUnkOuter is the unknown associated with the base filter
  hr = pUnkOuter->QueryInterface(__uuidof(IKsTopologyInfo),
                               (void **) &pKsTopologyInfo);
  if (!SUCCEEDED(hr))
  {
        printf("Unable to obtain IKsTopologyInfo %x\n", hr);
 goto errExit;
  }

  hr = FindExtensionNode(pKsTopologyInfo,
     GUID_EXTENSION_UNIT_DESCRIPTOR,
     &dwExtensionNode);
  if (FAILED(hr))
  {
        printf("Unable to find extension node : %x\n", hr);
 goto errExit;
  }

  hr = pKsTopologyInfo->CreateNodeInstance(
        dwExtensionNode,
   __uuidof(IExtensionUnit),
 (void **) &pExtensionUnit);
 if (FAILED(hr))
  {
        printf("Unable to create extension node instance : %x\n", hr);
 goto errExit;
  }

  hr = pExtensionUnit->get_PropertySize(1, &ulSize);
  if (FAILED(hr))
  {
        printf("Unable to find property size : %x\n", hr);
 goto errExit;
  }

  pbPropertyValue = new BYTE[ulSize];
  if (!pbPropertyValue)
  {
      printf("Unable to allocate memory for property value\n");
      goto errExit;
  }

  hr = pExtensionUnit->get_Property(1,ulSize, pbPropertyValue);
  if (FAILED(hr))
  {
      printf("Unable to get property value\n");
      goto errExit;
  }

  // assume the property value is an integer
  ASSERT(ulSize == 4);
  printf("The value of property 1 = %d\n", *((int *)
     pbPropertyValue));

编写 FindExtensionNode 函数的代码以查找必需的扩展单元节点并在 dwExtensionNode 中返回其 ID。 此 ID 在此示例代码中对 IKsTopologyInfo：： CreateNodeInstance 方法的后续调用中使用。

支持扩展单元的自动更新事件

hEvent = CreateEvent(NULL, FALSE, FALSE, NULL);
if (!hEvent)
{
    printf("CreateEvent failed\n");
    goto errExit;
}
Event.Set = KSEVENTSETID_VIDCAPNotify;
Event.Id = KSEVENT_VIDCAP_AUTO_UPDATE;
Event.Flags = KSEVENT_TYPE_ENABLE;

EventData.NotificationType = KSEVENTF_EVENT_HANDLE;
EventData.EventHandle.Event = hEvent;
EventData.EventHandle.Reserved[0] = 0;
EventData.EventHandle.Reserved[1] = 0;

// register for autoupdate events
hr = m_pKsControl->KsEvent(
    &Event, 
 sizeof(KSEVENT), 
    &EventData, 
 sizeof(KSEVENTDATA), 
    &ulBytesReturned);
if (FAILED(hr))
{
    printf("Failed to register for auto-update event : %x\n", hr);
 goto errExit;
}

// Wait for event for 5 seconds 
dwError = WaitForSingleObject(hEvent, 5000);

// cancel further notifications
hr = m_pKsControl->KsEvent(
    NULL, 
    0, 
    &EventData, 
 sizeof(KSEVENTDATA), 
    &ulBytesReturned);
if (FAILED(hr))  printf("Cancel event returns : %x\n", hr);

if ((dwError == WAIT_FAILED) || 
   (dwError == WAIT_ABANDONED) ||
   (dwError == WAIT_TIMEOUT))
{
    printf("Wait failed : %d\n", dwError);
 goto errExit;
} 
printf("Wait returned : %d\n", dwError);

// handle the autoupdate event..

FindExtensionNode

HRESULT FindExtensionNode(IKsTopologyInfo *pKsTopologyInfo, GUID guid, DWORD *node)
{
    HRESULT hr = E_FAIL;
    DWORD dwNumNodes = 0;
    GUID guidNodeType;
    IKsControl *pKsControl = NULL;
    ULONG ulBytesReturned = 0;
    KSP_NODE ExtensionProp;

    if(!pKsTopologyInfo || !node)
        return E_POINTER; 

    // Retrieve the number of nodes in the filter
    hr = pKsTopologyInfo->get_NumNodes(&dwNumNodes);
    if(!SUCCEEDED(hr))
        return hr;
    if(dwNumNodes == 0)
        return E_FAIL;


    // Find the extension unit node that corresponds to the given GUID
    for(unsigned int i = 0; i < dwNumNodes; i++)
    {
        hr = E_FAIL;
        pKsTopologyInfo->get_NodeType(i, &guidNodeType);
        if(IsEqualGUID(guidNodeType, KSNODETYPE_DEV_SPECIFIC))
        {
            printf("found one xu node\n");
            IExtensionUnit*   pExtensionUnit = NULL;
          hr = pKsTopologyInfo->CreateNodeInstance(i, __uuidof(IExtensionUnit), (void **)&pExtensionUnit);
            if(SUCCEEDED(hr))
            {
                ExtensionProp.Property.Set = guid;
                ExtensionProp.Property.Id = 0;
                ExtensionProp.Property.Flags = KSPROPERTY_TYPE_SETSUPPORT | KSPROPERTY_TYPE_TOPOLOGY;
                ExtensionProp.NodeId = i;
                ExtensionProp.Reserved = 0;

                *node = i;
                return hr;

                /*
                hr = pKsControl->KsProperty((PKSPROPERTY)&ExtensionProp, sizeof(ExtensionProp), NULL, 0, &ulBytesReturned);
                if(SUCCEEDED(hr))
                {
                    *node = i;
                    break;
                }
                */
            }
            else
            {
                printf("CreateNodeInstance failed - 0x%x\n", hr);
            }
        }
    }

    return hr;
}

参考资料：
https://docs.microsoft.com/en-us/windows-hardware/drivers/stream/extension-unit-plug-in-architecture