just posted a possible solution in the bug reports forum:
https://forum.cockos.com/showthread.php?t=222434
bottom line is there seem to be no problems with video if i save, close reaper, reopen reaper after adding a video file. seems very clunky but i tested 17 different video file formats and they all worked with a save, close, reopen procedure. none worked unless i did that.
thanks,
babag