Fastest method of screen capturing on Windows

Question

I want to write a screencasting program for the Windows platform, but am unsure of how to capture the screen. The only method I'm aware of is to use GDI, but I'm curious whether there are other ways to go about this, and, if there are, which incurs the least overhead? Speed is a priority.

The screencasting program will be for recording game footage, although, if this does narrow down the options, I'm still open for any other suggestions that fall out of this scope. Knowledge isn't bad, after all.

Edit: I came across this article: Various methods for capturing the screen. It has introduced me to the Windows Media API way of doing it and the DirectX way of doing it. It mentions in the Conclusion that disabling hardware acceleration could drastically improve the performance of the capture application. I'm curious as to why this is. Could anyone fill in the missing blanks for me?

Edit: I read that screencasting programs such as Camtasia use their own capture driver. Could someone give me an in-depth explanation on how it works, and why it is faster? I may also need guidance on implementing something like that, but I'm sure there is existing documentation anyway.

Also, I now know how FRAPS records the screen. It hooks the underlying graphics API to read from the back buffer. From what I understand, this is faster than reading from the front buffer, because you are reading from system RAM, rather than video RAM. You can read the article here.

Answer 1

This is what I use to collect single frames, but if you modify this and keep the two targets open all the time then you could "stream" it to disk using a static counter for the file name. - I can't recall where I found this, but it has been modified, thanks to whoever!

void dump_buffer()
{
   IDirect3DSurface9* pRenderTarget=NULL;
   IDirect3DSurface9* pDestTarget=NULL;
     const char file[] = "Pickture.bmp";
   // sanity checks.
   if (Device == NULL)
      return;

   // get the render target surface.
   HRESULT hr = Device->GetRenderTarget(0, &pRenderTarget);
   // get the current adapter display mode.
   //hr = pDirect3D->GetAdapterDisplayMode(D3DADAPTER_DEFAULT,&d3ddisplaymode);

   // create a destination surface.
   hr = Device->CreateOffscreenPlainSurface(DisplayMde.Width,
                         DisplayMde.Height,
                         DisplayMde.Format,
                         D3DPOOL_SYSTEMMEM,
                         &pDestTarget,
                         NULL);
   //copy the render target to the destination surface.
   hr = Device->GetRenderTargetData(pRenderTarget, pDestTarget);
   //save its contents to a bitmap file.
   hr = D3DXSaveSurfaceToFile(file,
                              D3DXIFF_BMP,
                              pDestTarget,
                              NULL,
                              NULL);

   // clean up.
   pRenderTarget->Release();
   pDestTarget->Release();
}