Playing videos still prevents the system from entering sleep mode or activating the screensaver

Discussed in https://github.com/MicrosoftEdge/WebView2Feedback/discussions/4956

^{Originally posted by Taiizor November 29, 2024}
Hello,

I am using WebView2 in my WPF project to play a looping video. However, as long as the window remains open, neither the screensaver activates nor does the system go to sleep.

Below is a code snippet I tried as a solution, but it didn't resolve the issue:

[DllImport("user32.dll", SetLastError = true)]
private static extern void SetThreadExecutionState(uint esFlags);

private const uint ES_CONTINUOUS = 0x80000000;
private const uint ES_SYSTEM_REQUIRED = 0x00000001;
private const uint ES_DISPLAY_REQUIRED = 0x00000002;

private void AllowScreenSaver()
{
    SetThreadExecutionState(ES_CONTINUOUS);
}

private void PreventScreenSaver()
{
    SetThreadExecutionState(ES_CONTINUOUS | ES_DISPLAY_REQUIRED | ES_SYSTEM_REQUIRED);
}

Additionally, I tried using launcher arguments like --disable-background-timer-throttling --disable-renderer-backgrounding --disable-backgrounding-occluded-windows, but these didn’t work either.

Interestingly, the issue is resolved in MpvPlayer by setting the stop-screensaver option to no. When reviewing its code, I noticed that it uses ES_CONTINUOUS.

https://github.com/mpv-player/mpv/blob/a283f66ede58e0182ac8cd4c930238144427fa74/video/out/w32_common.c#L2326

case VOCTRL_KILL_SCREENSAVER:
	w32->disable_screensaver = true;
	SetThreadExecutionState(ES_CONTINUOUS | ES_SYSTEM_REQUIRED | ES_DISPLAY_REQUIRED);
	return VO_TRUE;
case VOCTRL_RESTORE_SCREENSAVER:
	w32->disable_screensaver = false;
	SetThreadExecutionState(ES_CONTINUOUS);
	return VO_TRUE;

Start by reproducing the behavior in the described WPF project with WebView2 and review the SetThreadExecutionState calls shown in the issue. Compare the behavior with mpv's video/out/w32_common.c handling of VOCTRL_KILL_SCREENSAVER and VOCTRL_RESTORE_SCREENSAVER. Done means identifying why looping video prevents sleep or the screensaver and documenting or validating a supported resolution.