The audio and video streams need to be synchronized with each other, so that you don't hear people before they have opened their mouth. Usually, SMPlayer works perfectly.
But with some videos, the synchronization is off by a sizeable fraction of a second when the video is first played.
The workaround is to click the stop button, then the run button, then (because the video screen has disappeared entirely and only the audio is heard) the fullscreen button.
I would deeply appreciate it if these bugs could please be fixed. I can supply SMPlayer develpers with videos that fail in this way.
Version: 18.6.0 (revision 9075) (32-bit)