Use DirectShow to drive the camera

There are several ways to drive a small camera. using DirectShow to drive the camera is more flexible, and there are simple and complex but more effective methods. This article only introduces simple methods, hope to communicate with you!
When using DirectShow to use a camera, it is generally required that the camera driver be In the WDM format. Of course, some older driver formats, DirectShow, are also supported. DirectShow uses the filter graph manager to communicate with upper-layer applications.ProgramAnd the driver of the lower layer. DirectShow supports camera capturing through a kind of stuff called the capture filter. A capture filter has multiple pins, in which the Preview (PreView) the plug-in can be used to display the hidden image.

DirectShow uses several com interfaces to control the video capture process. igraphbuilder is used to create a filter. icapturegraphbuilder2 is used to establish a connection with the underlying driver, ivideowindow, imediacontrol, imediaeventex controls the video windows, playing processes, and event responses of the entire process, respectively,

The following is a routine:

Ccomqiptr m_pvw;

Ccomqiptr m_pmc;

Ccomqiptr m_pme;

Ccomptr m_pgraph;

Ccomptr m_pcapture;

DWORD m_dwgraphregister;

Bool binit (hwnd)

{

Hresult hr;

// Obtain the interface

HR = cocreateinstance (clsid_filtergraph, null, clsctx_inproc, iid_igraphbuilder, (void **) & m_pgraph );

If (failed (HR ))

Return false;

HR = cocreateinstance (clsid_capturegraphbuilder2, null, clsctx_inproc,

Iid_icapturegraphbuilder2, (void **) & m_pcapture );

If (failed (HR ))

Return false;

M_pmc = m_pgraph;

M_pvw = m_pgraph;

M_pme = m_pgraph;

// Get the message

M_pme-> setpolicywindow (oahwnd) (m_hwnd = hwnd), wm_graph1_y, 0 );

// Connect filtering and capturing

M_pcapture-> setfiltergraph (m_pgraph );

// Device connection

// Enumerate Devices

Ccomptr pcde = NULL;

Ccomptr PEM = NULL;

HR = cocreateinstance (clsid_systemdeviceenum, null, clsctx_inproc,

Iid_icreatedevenum, (void **) & pcde );

If (failed (HR ))

Return false;

Pcde-> createclassenumerator (clsid_videoinputdevicecategory, & PEM, 0 );

If (PEM = NULL)

Return false;

Ccomptr PM = NULL;

Ulong cfetched;

Ccomptr PBF = NULL;

If (PEM-> next (1, & PM, & cfetched) = s_ OK)

{

PM-> bindtoobject (0, 0, iid_ibasefilter, (void **) & Pbf );

PM. Release ();

}

Else

{

Return false;

}

// Add the device to graph

HR = m_pgraph-> addfilter (PBF, l "video capture ");

If (failed (HR ))

Return false;

// Connect a source plug-in

HR = m_pcapture-> renderstream (& pin_category_preview, & mediatype_video, PBF, null, null );

If (failed (HR ))

Return false;

PBF. Release ();

// Set the video window

// Sets a subwindow of the main video window.

HR = m_pvw-> put_owner (oahwnd) hwnd );

If (failed (HR ))

Return false;

// Set the window style

M_pvw-> put_windowstyle (ws_child | ws_clipchildren );

If (failed (HR ))

Return false;

// Set the window size

Crect rectclient;

Getclientrect (hwnd, rectclient );

M_pvw-> setwindowposition (0, 0,320,240 );

// Set the visualization

HR = m_pvw-> put_visible (oatrue );

If (failed (HR ))

Return false;

// Add the object to the running Object List

Ccomptr prot;

Getrunningobjecttable (0, & prot );

Wchar C [128];

WsprintfW (C, L "filtergraph % 08x PID % 08x", (dword_ptr) m_pgraph.p, getcurrentprocessid ());

HR = createitemmoniker (L "! ", C, & PM );

If (failed (HR ))

Return false;

HR = prot-> Register (rotflags_registrationkeepsalive, m_pgraph, PM, & m_dwgraphregister );

PM. Release ();

Return false;

}