Windows 媒体基金会枚举相机设备 [英] Windows media foundation enumerating Camera devices
问题描述
我想使用 Windows Media Foundation 枚举计算机上的相机设备，我在 Microsoft 上使用了代码:http://msdn.microsoft.com/en-us/library/windows/desktop/dd940326(v=vs.85).aspx我在这里复制了他们使用的相同代码:http://msdn.microsoft.com/en-us/library/windows/desktop/ee663604(v=vs.85).aspx
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
当我使用他们的代码时，我得到了我的网络摄像头设备名称，但是我的代码没有找到任何相机捕获设备.我可以找到原因.
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.
代码如下:
#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;
}
推荐答案
在开始调用其他 Media Foundation API 函数之前，您应该执行 MFStartup(MF_VERSION);.
You are expected to do MFStartup(MF_VERSION); before you start calling other Media Foundation API functions.
然后在 MFEnumDeviceSources 下面一行初始化之前打印 m_cDevices.
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);
解决此问题后，您的代码将开始为您提供设备.
Having this fixed, your code will start getting you the devices.
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