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    <p>There are several APIs from Microsoft which provide access to image data.</p> <ul> <li>Twain: Used for single image capture from scanners, etc.</li> <li>WIA: This seems to have degenerated to a single image codec library.</li> <li>VfW: A very old (Win16) API which really works only Video-File encoding/decoding, but has support for some video acquisition.</li> <li>DirectShow: previously part in the DirectX SDK, currently in the Platform SDK. This is the place to go for current (general) streaming solutions.</li> <li>Windows Media/Media Foundation: This seems more to be geared at video playback/reencoding.</li> <li>Manufacturer Specific Libraries: Pylon/Halcon/Imaging Control/...</li> </ul> <p>DirectShow specific :</p> <p>To create image acquisition devices under windows, you have to provide either a device (driver) which implements the streamclasses interfaces (or newer Avstream) or you have to write a usermode COM object which has to be added to the VideoInputCategory enumerator.</p> <p>The Avstream sample provides everything for a real image acquisition device. Only the lower layer for the actual device really is missing.</p> <p>If you can design a device, you should either create it DCAM or UVC compatible. For both there are built-in drivers supplied by windows.</p> <hr> <p>How to write a software source device :</p> <p>You have to create a DirectShow filter which provides at least one output pin and register this under the VideoInputCategory. There may be several interfaces certain applications require from a capture application, but these depend on the application itself. Simple applications to try out filters are GraphEdit and AMCap which are supplied in the Plattform SDK.</p> <p>Some code :</p> <pre><code>#include &lt;InitGuid.h&gt; #include &lt;streams.h&gt; const AMOVIESETUP_MEDIATYPE s_VideoPinType = { &amp;MEDIATYPE_Video, // Major type &amp;MEDIATYPE_NULL // Minor type }; const AMOVIESETUP_PIN s_VideoOutputPin = { L"Output", // Pin string name FALSE, // Is it rendered TRUE, // Is it an output FALSE, // Can we have none FALSE, // Can we have many &amp;CLSID_NULL, // Connects to filter NULL, // Connects to pin 1, // Number of types &amp;s_VideoPinType // Pin details }; const AMOVIESETUP_FILTER s_Filter = { &amp;CLSID_MyFilter, // Filter CLSID L"bla", // String name MERIT_DO_NOT_USE, // Filter merit 1, // Number pins &amp;s_VideoOutputPin // Pin details }; REGFILTER2 rf2; rf2.dwVersion = 1; rf2.dwMerit = MERIT_DO_NOT_USE; rf2.cPins = 1; rf2.rgPins = s_Filter.lpPin; HRESULT hr = pFilterMapper-&gt;RegisterFilter( CLSID_MyFilter, _FriendlyName.c_str(), 0, &amp;CLSID_VideoInputDeviceCategory, _InstanceID.c_str(), &amp;rf2 ); if( FAILED( hr ) ) { return false; } std::wstring inputCat = GUIDToWString( CLSID_VideoInputDeviceCategory ); std::wstring regPath = L"CLSID\\" + inputCat + L"\\Instance"; win32_utils::CRegKey hKeyInstancesDir; LONG rval = openKey( HKEY_CLASSES_ROOT, regPath, KEY_WRITE, hKeyInstancesDir ); if( rval == ERROR_SUCCESS ) { win32_utils::CRegKey hKeyInstance; rval = createKey( hKeyInstancesDir, _InstanceID, KEY_WRITE, hKeyInstance ); .... </code></pre> <p>_InstanceID is a GUID created for this 'virtual device' entry.</p>
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