My system is 4770K 8 GB RAM Win 10 1903 various AMD cards (7970 - RX 580) I tried reencoding the BIK video file (BIK not SMK files, sorry I mentioned that incorrectly) and even with a black (empty) BIK vidoe file it still shows a blue vertical line when the game plays it, must be some sort of error possibly with the Source Engine. Not much support for Postal 3, so any ideas anyone? A way to just not render those far right vertical pixels on the end of the video would fix it. I did find a way to force the Window to be fullscreen without a border with a scripting utility, except that makes the in game menu hard to navigate because now they are off about ten pixels due to the removal of the top window border, but it removes the blue pixels. So trade one problem for another.
The easiest way might be to find a utility that could just render those last few vertical lines as black and then it wouldn't look so distracting, I used to have a utility for Win 98 that would do that, but I can't find a modern day equivalent, something where you could move or reduce the size of the Window even when full screen.
With an old CRT and old games this was fairly easy to fix by simply stretching the image further than the tube (bezel) and those ugly pixels wouldn't be shown anymore, I don't know a way to do that on an LCD.
All in all, Postal 3 runs great even on the 7970 all the way to RX 580, but the videos that play during the game look distracting, I've tried all my tricks I can think of.