QMediaPlayer::setPosition(qint64) funny behavior

[RegisPower]

Hello,

I am currently writing a program in which I included a video player. I am using Qt5.7 and only Qt modules (QtCharts, QtMultimedia) on Mac OS X 10.11.5.

In my program, a QMediaPlayer allows me to play a video (in mp4 file format). I can control the position of the video with a QSlider but there are also other methods that can send a new position to the player.

My problem is the following :
When I use the "setPosition(qint64)" method of the QMediaPlayer object I created, the position returned by the "position()" afterwards is never the same I wanted initially. Moreover, the new position is really out of sync with the position I inputted (like more than 20 seconds).
I need the less delay possible between the position I input and the position the player really accepts.
The only lead I have on my problem is that the video is of bad quality but I do not know much about video properties and I especially do not know which properties can cause this behavior.

Thank you for your replies.