Windows media foundation enumerating Camera devices

问题

I would like to enumerate the camera devices on my computer using Windows Media Foundation, I used the code on Microsoft : http://msdn.microsoft.com/en-us/library/windows/desktop/dd940326(v=vs.85).aspx I reproduced the same code they use here : http://msdn.microsoft.com/en-us/library/windows/desktop/ee663604(v=vs.85).aspx

When I used their code I get my webcam device name, however my code doesn't find any camera capture device. I'm enable to find why.

Here is the code :

    #pragma once
#include <new>
#include <windows.h>
#include <mfapi.h>
#include <mfidl.h>
#include <mfreadwrite.h>
#include <Wmcodecdsp.h>
#include <assert.h>
#include <Dbt.h>
#include <shlwapi.h>
#include <mfplay.h>

#include <iostream>


const UINT WM_APP_PREVIEW_ERROR = WM_APP + 1;    // wparam = HRESULT

class DeviceList
{
    UINT32      m_cDevices; // contains the number of devices
    IMFActivate **m_ppDevices; // contains properties about each device

public:
    DeviceList() : m_ppDevices(NULL), m_cDevices(0)
    {

    }
    ~DeviceList()
    {
        Clear();
    }

    UINT32  Count() const { return m_cDevices; }

    void    Clear();
    HRESULT EnumerateDevices();
    HRESULT GetDevice(UINT32 index, IMFActivate **ppActivate);
    HRESULT GetDeviceName(UINT32 index, WCHAR **ppszName);
};




#include "DeviceList.h"

/*
* A templated Function SafeRelease releasing pointers memories
* @param ppT the pointer to release
*/

template <class T> void SafeRelease(T **ppT)
{
    if (*ppT)
    {
        (*ppT)->Release();
        *ppT = NULL;
    }
}



/*
* A function which copy attribute form source to a destination
* @ param pSrc is an Interface to store key/value pairs of an Object
* @ param pDest is an Interface to store key/value pairs of an Object
* @ param GUID is an unique identifier
* @ return HRESULT return errors warning condition on windows
*/

HRESULT CopyAttribute(IMFAttributes *pSrc, IMFAttributes *pDest, const GUID& key);




/*
* A Method form DeviceList which clear the list of Devices
*/

void DeviceList::Clear()
{
    for (UINT32 i = 0; i < m_cDevices; i++)
    {
        SafeRelease(&m_ppDevices[i]);
    }
    CoTaskMemFree(m_ppDevices);
    m_ppDevices = NULL;

    m_cDevices = 0;
}


/*
* A function which enumerate the list of Devices.
* @ return HRESULT return errors warning condition on windows
*/
HRESULT DeviceList::EnumerateDevices()
{
    HRESULT hr = S_OK;
    IMFAttributes *pAttributes = NULL;

    this->Clear();

    // Initialize an attribute store. We will use this to
    // specify the enumeration parameters.
    std::cout << "Enumerate devices" << std::endl;
    hr = MFCreateAttributes(&pAttributes, 1);

    // Ask for source type = video capture devices
    if (SUCCEEDED(hr))
    {
        std::cout << "Enumerate devices" << std::endl;
        hr = pAttributes->SetGUID(
            MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE,
            MF_DEVSOURCE_ATTRIBUTE_SOURCE_TYPE_VIDCAP_GUID
            );
    }
    // Enumerate devices.
    if (SUCCEEDED(hr))
    {
        std::cout << "Enumerate devices:" << m_cDevices << std::endl;
        hr = MFEnumDeviceSources(pAttributes, &m_ppDevices, &m_cDevices);
    }

    SafeRelease(&pAttributes);

    return hr;
}


/*
* A function which copy attribute form source to a destination
* @ param index the index in an array
* @ param ppActivate is an Interface to store key/value pairs of an Object
* @ return HRESULT return errors warning condition on windows
*/


HRESULT DeviceList::GetDevice(UINT32 index, IMFActivate **ppActivate)
{
    if (index >= Count())
    {
        return E_INVALIDARG;
    }

    *ppActivate = m_ppDevices[index];
    (*ppActivate)->AddRef();

    return S_OK;
}


/*
* A function which get the name of the devices
* @ param index the index in an array
* @ param ppszName Name of the device
*/


HRESULT DeviceList::GetDeviceName(UINT32 index, WCHAR **ppszName)
{
    std::cout << "Get Device name" << std::endl;
    if (index >= Count())
    {
        return E_INVALIDARG;
    }

    HRESULT hr = S_OK;

    hr = m_ppDevices[index]->GetAllocatedString(
        MF_DEVSOURCE_ATTRIBUTE_FRIENDLY_NAME,
        ppszName,
        NULL
        );

    return hr;
}


#include <iostream>
#include "DeviceList.h"

HRESULT UpdateDeviceList()
{
    HRESULT hr = S_OK;
    WCHAR *szFriendlyName = NULL;

    DeviceList g_devices;


    g_devices.Clear();

    hr = g_devices.EnumerateDevices();

    if (FAILED(hr)) { goto done; }
    std::cout << "Nb devices found:"<< g_devices.Count() << std::endl;

    for (UINT32 iDevice = 0; iDevice < g_devices.Count(); iDevice++)
    {
        //std::cout << "" << std::endl;
        hr = g_devices.GetDeviceName(iDevice, &szFriendlyName);
        if (FAILED(hr)) { goto done; }
        std::cout << szFriendlyName << std::endl;
        // The list might be sorted, so the list index is not always the same as the
        // array index. Therefore, set the array index as item data.
        CoTaskMemFree(szFriendlyName);
        szFriendlyName = NULL;
    }
    std::cout << "End of EnumDeviceList" << std::endl;
done:
    return hr;
}



int main()
{
    std::cout <<"Main" << std::endl;
    UpdateDeviceList();
while (1);
return 0;

}

回答1:

You are expected to do MFStartup(MF_VERSION); before you start calling other Media Foundation API functions.

Then you print m_cDevices before it is getting initialized one line below by MFEnumDeviceSources.

    std::cout << "Enumerate devices:" << m_cDevices << std::endl;
    hr = MFEnumDeviceSources(pAttributes, &m_ppDevices, &m_cDevices);

Having this fixed, your code will start getting you the devices.

来源：https://stackoverflow.com/questions/23144501/windows-media-foundation-enumerating-camera-devices