How to stop ring tone before accepting or refusing an incoming call?

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C++

C

Windows

Mobile

In Windows Mobile 6.1, I need to stop the ring tone before accepting or refusing an incoming call. And in the mean time, I need to play a video.

I tried to stop the ring tone by simulate a key press with VK_F6(volume -):

const int KEYEVENTF_KEYDOWN = 0x00;
keybd_event(VK_F6, 0, KEYEVENTF_KEYDOWN, 0);
keybd_event(VK_F6, 0, KEYEVENTF_KEYUP, 0);

Though I could stop the sound, I can not hear the sound of the video I am then playing.

What can I do to resolve this problem?