[Interest] QAbstractVideoSurface::present - videoframe start/endtime always -1 on windows

Ola Røer Thorsen ola at silentwings.no
Thu Jun 13 13:20:15 CEST 2013


I've created a custom video player using QMultimedia, that plays back 
certain video files that are to be post-processed frame-by-frame. The 
post-process depends on each video frame's start time. I'm using the Qt 
5.1 beta release (I use the new desktop QML features).

I've created a video surface class that inherits QAbstractVideoSurface, 
register this in QMediaplayer, and I get each frame in my own 
implementation of QAbstractVideoSurface::present.

On Linux, this works flawlessly, each QVideoFrame have proper values for 
QVideoFrame::startTime() and endTime(). However on windows, start- and 
endtimes are always -1 (invalid).

I try now to look up the current position in the mediaplayer each time 
present is called, but this is not really precise enough. Anyone know 
how to make this work? I've tried various video file formats but they 
all give the same -1 values.

Maybe there is a bug in the windows backend (WMF?). I tried looking into 
the source code - at first glance it looks allright (mftvideo.cpp at 
line 638), but while googling further into it I found this page here,
where further calculations are needed as the sample times are relative 
to a "presentation clock", so maybe it can't work like it's implemented 

Best regards

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