luis lenders wrote:
As to the title, avicap32 won't implement the callback function, but your application will do that. avicap32 only will call it.
Hi , i would like to implement this function: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/multim
ed/htm/_win32_cappreview.asp
Well this function (or rather a macro) is only to enable or disable the preview mode. There isn't any callback function I can see here. It is rather about a preview of the actual capture data in the capture window itself. You can install a frame callback with capSetCallbackOnFrame() and this callback function will be called for every frame BEFORE it is diplayed in the preview.
Here fpProc is a pointer to the preview callback function Applications use this to get access to the videodata. Right now i already have a preview window.
If i'm correct it is similar to this
function:http://msdn.microsoft.com/library/default.asp?
url=/library/en-us/multimed/htm/_win32_capvideostreamcallback.asp
As far as I understand it, the preview callback as you call it is rather installed by the capSetCallbackOnFrame() macro and ultimately by the WM_CAP_SET_CALLBACK_FRAME message. MSDN doesn't directly specify the actual callback prototype of this callback, but it if you search further you can see that the capVideoStreamCallback() prototype is both used for the WM_CAP_SET_CALLBACK_FRAME and WM_CAP_SET_CALLBACK_VIDEOSTREAM callbacks.
Here the structure LPVIDEOHDR lpVHdr contains the information about the videodata. My question is how all of this could be implemented; right now i have :
case WM_CAP_SET_CALLBACK_FRAME:
{ ^^ You can only declare variables in standard C at the beginning of a block and since Wine has to be compilable in standard C you need to add curly braces before you can declare variables.
LPVIDEOHDR lpVideoHdr; //defined in vfw.h typedef LRESULT (CALLBACK * CAPVIDEOCALLBACK)(HWND hwnd, LPVIDEOHDR
lpVideoHdr);
CAPVIDEOCALLBACK *framecallback = (CAPVIDEOCALLBACK*)lParam;
You need to store this callback function pointer somewhere in the capture window. This could be done by adding the callback pointers to the structure which holds all the different runtime parameters for the capture process, such as the CAPSTATUS, CAPPARAMS, CAPDRIVERCAPS and probably some more but private data etc structures. The pointer to this whole structure will be probably added to the capture window as an ATOM or maybe (but probably less preferable) as user data.
{so what goes here? }
Not much more than what I explained above. The message loop of your capture window will then have to check for every incoming frame if frame callback is set to on (non-NULL) and in that case call the saved callback pointer with the actual data.
So how could i pass the data in lpVideoHdr to the application? Any help appreciated as i'm still quite a beginner in this :)
You won't do that in the WM_CAP_SET_CALLBACK_FRAME message handler. Rather your message loop will have to do some idle processing, such as generating a regular WM_something message in which the external video data is read in and then all the necessary processing is done such as passing the captured data to the frameCallback if that is enabled, then doing the preview or overlay operation if on, and after that pass the data to the videoStreamCallback etc.
But I think your major problem here is not the capSetPreview macro or rather its message implementation in the first place, but rather the fact that avicap32.dll is basically an empty placeholder in current wine. You will need to implement quite something more before you can even worry about capSetPreview().
Rolf Kalbermatter