Playbar does not wait for sidebar video

This is the name of a 2008 discussion without a proper solution.

I have the same issue with Presenter 10, quite a few years later...

I'm importing mp4 videos in the sidebar video with medium quality option but when playing the presentation the slide starts without waiting the video to fully buffer.

Control preloading is enabled

Here is the presentation OGC Indoor GML

Please help

Thanks in advance