I’ve tried a few more tests, but with different file formats (codecs), and to summarise the problem only seems to occur with MPEG2 videos with a frame rate of 50 Hz. At least thats 50Hz as detected by OSMC/Kodi as shown in the detailed file info and in the debug monitoring info at the Top LHS of the screen (i.e. FR), whereas media info (as in a previous post) shows the file has a frame rate of 25Hz.
I tried 1080p H.264, 2160p H.265 and MPEG2 but with different frame rates other than 25Hz and these all seemed to be OK.
So it seems that MPEG2s with FR of 25Hz (50Hz) cause this problem which is probably related to the interlace properties of the video ?? Is the HW decode de-interlacing properly with respect to time … ?
Looks like this might be related to this earlier post - Vero V audio sync issue since last update - #41 by ecs007