I need help in VB6 !

I have a MCI Multimedia Control and I want to play and process some video in a pictureBox (from different source: Avi files or video hardware).
I have a dll for image processing which need to copy the picture into the memory (for processing). It requires a Device Context and the hWnd property of the pictureBox:

Code:
ImageToMemory Picture1.hDC, Picture1.hWnd, Width, Height
The hWnd property doesn't seem to be important. So I don't know how to have the device context for a video stream that I could use with this function.

Moreover, user can move and resize a region of interest on the pictureBox with the mouse.

So, in a first time, I used two pictureBoxes, one was invisible and contained the original picture and the second picture used for display. When this picture was repaint I used paintpicture method and this worked fine.

Now, I want to process some video with the MMcontrol, so I had to change the paintpicture method into BitBlt.

For simple image I create a DC with CreatCompatibleDC and I use SelectObject to affect the bitmap I want.

But for video I can't find a DC of the MMcontrol except if I set MMcontrol.hWndDisplay to Picture1.hWnd and Picture1 is visible.

If Picture1 if partially hidden or not visible the bitblt function copy that is over the picture... and that very evil...


Do you understand my problem ?