March 27th, 2014, 04:47 PM
Blocking Keyboard Play/Pause Button in Win 8
I am writing an application that needs to temporarily disable the Play/Pause button that appears on multimedia keyboards.
Normally, a key can be blocked quite easily by installing a low level keyboard hook (WH_KEYBOARD_LL) where the KeyboardProc intercepts the key (in this case VK_MEDIA_PLAY_PAUSE) and returns a "1" instead of calling CallNextHookEx. I have tried this with other keys (including the Windows key VK_LWIN) and this works perfectly. I also have no problems with this method under Windows 7 where all keys, including VK_MEDIA_PLAY_PAUSE get blocked.
Windows 8 is a different story. When my application has input focus, everything works as expected, meaning the VK_MEDIA_PLAY_PAUSE key gets blocked and no other application responds to it. However, when my application loses focus, my hook procedure gets called (this was verified by sending out a OutputDebugString) but other applications respond to key even though I return a "1". As soon as my app gets focus again, everything is block as it should.
After some investigation, I found that the multimedia keys not only generate keystrokes but also generate WM_APPCOMMAND messages so I added ShellProc (WH_SHELL) hook with the following hook procedure:
LRESULT __declspec(dllexport)__stdcall CALLBACK ShellProc(int nCode,WPARAM wParam,LPARAM lParam)
// Do we have to handle this message?
if (nCode == HSHELL_APPCOMMAND)
// Process the hook if the hNotifyWnd window handle is valid
short AppCommand = GET_APPCOMMAND_LPARAM(lParam);
OutputDebugString(">>>>>ShellProc got a media command");
// Call the next handler in the chain
return CallNextHookEx (hsh, nCode, wParam, lParam);
This procedure is only getting called when my app has input focus. Whenever I have input focus and return "1" the Play/Pause command gets blocked. As soon as I lose focus the procedure does not get called/hooked.
Anyone have any idea as to what is going on? As I have mentioned, the code works for other keys, just not the multimedia keys.
Alternatively, can anyone suggest another way of blocking the multimedia keyboards Play/Pause button?
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