WM_CAP_SET_CALLBACK_YIELD message

The WM_CAP_SET_CALLBACK_YIELD message sets a callback function in the application. AVICap calls this procedure when the capture window yields during streaming capture. You can send this message explicitly or by using the capSetCallbackOnYield macro.

WM_CAP_SET_CALLBACK_YIELD 
wParam = (WPARAM) 0; 
lParam = (LPARAM) (LPVOID) (fpProc); 

Parameters

fpProc

Pointer to the yield callback function, of type capYieldCallback. Specify NULL for this parameter to disable a previously installed yield callback function.

Return Value

Returns TRUE if successful or FALSE if streaming capture or a single-frame capture session is in progress.

Remarks

Applications can optionally set a yield callback function. The yield callback function is called at least once for each video frame captured during streaming capture. If a yield callback function is installed, it will be called regardless of the state of the fYield member of the CAPTUREPARMS structure.

If the yield callback function is used, it must be installed before starting the capture session and it must remain enabled for the duration of the session. It can be disabled after streaming capture ends.

Applications typically perform some type of message processing in the callback function consisting of a PeekMessage, TranslateMessage, DispatchMessage loop, as in the message loop of a WinMain function. The yield callback function must also filter and remove messages that can cause reentrancy problems.

An application typically returns TRUE in the yield procedure to continue streaming capture. If a yield callback function returns FALSE, the capture window stops the capture process.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Header	Vfw.h

See also

Video Capture

Video Capture Messages