sound of every original video progressively shifts

[Papou]

Avidemux 2.7.4 on Ubuntu 18.04 shifts the sound of unaltered video files found on e.g. Youtube.
That shift is progressive (not a matter of initial shift).
Sound progressively gets more and more out of synch up to a mute sequence at the end of the video.
If I stop and restart playing, it gets back in synch.
It works as if video or sound rate was badly calculated while playing but not while positioning.
It looks like some videos are more affected than others by that phenomenon and some not at all or unnoticeably.
It happens with a fresh ~/.aviidemux6.
What can it be or what can be done to find a reason?
TIA.

[eumagga0x2a]

If it happens only with high resolution videos, then the video decoder and the video output can't handle the specified fps in real time on your hardware with your Avidemux configuration. If you have a NVIDIA graphics card running with their closed-source driver, enable VDPAU both for display and decoding. If you have Intel integrated graphics, enable LibVA decoding + output. This will help a lot for video using codecs, supported by your hardware.

In any case, I would very much recommend using a more current build.