[Qt-interest] QTimer on Windows in Unreliable for Small (16ms - 30ms) Delays

[Jeffrey Brendecke]

I have read that the WM_TIMER message in Windows is very low priority, which 
would be a problem should that be used. You mentioned earler:

> I've even
> seen metion of something like qt_win_simple_timers or something like
> that - compile errors, didn't help. I tried using windows timer queues -
> I forget the function names - but compile errors there.

It might be worth checking out the various Windows programmer forums for 
assistance on getting them to work. I cannot recommend any forum in 
particular.


On Saturday 05 September 2009 21:36:40 Josiah Bryan wrote:
> Pau Garcia i Quiles wrote:
> > We have seen issues with QTimer on Windows, too, when you ask for a
> > tiny interval or the system is under high load. The reason for this
> > broken behavior is QTimer essentially counts events on Windows. A
> > better approach would be to call GetTickCount or
> > QueryPerformanceCounter. On Unix, QTimer uses clock_gettime, which
> > works fine.
>
> Hmmm...interesting. I'll have to mull that one over.
>
> > For now we are using ACE timers (
> > http://www.cs.wustl.edu/~schmidt/ACE.html ) instead of QTimers where
> > we see problems.
>
> Could you provide any code examples or quick snippets to illustrate the
> use of ACE timers in Qt-based code? It would help a lot!
>
> > That being, said, your problem is probably not due to QTimer but due
> > to the latency of the Phonon backend (DirectX under Windows).
> > Different backends behave different: some have a longer latency than
> > others. Some will support a feature, others won't. This very issue,
> > failing to playing very short media files, we have found to happen
> > with DirectX (Windows), Xine (Linux), GStreamer (Linux) and VLC
> > (Linux). VLC behaved a bit better than the others did but still failed
> > in some cases.
>
> I'm actually not even using Phonon - using ffmpeg directly (libavcodec
> and friends) to decode the video streams, buffer the frames using
> QQueue<QFFMpegVideoFrame>, and render the frames with appros delays
> calculated from the pts of each frame. So, in this case, DirectX or Xine
> or GStreamer aren't even being touched. Of course, since ffmpeg and
> friends are the backend for VLC, thats a different story - but so far,
> on linux, I have not experienced a single problem with the timers like I
> have on windows.
>
> I would, though, appreciate any code samples you could spare on ACE
> timers - I'll gladly explore that route.
>
> Thanks!
> -josiah
>
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