There are 2 issues I can see causing this. If you are using a program to watch the videos that has a bug which causes this or Your graphics card is going bad. Try troubleshooting by watching the videos with some other programs. If it seems pretty universal, then I would say there is definitely a hardware level issue. Another thing you could try is using another monitor. If that monitor does not have the same ghosting affect, then it is an issue with the display. If it does, then its an issue with the GPU. However, it could still be a GPU issue even if the image does not ghost on the monitor. Might be time to bring it in to the shop or look into replacing parts!
Apple is very against self repairs, my guess would be your issue is due to it being an ‘unauthorized’ repair. I would suggest taking it to an apple certified repair shop (or at least a repair shop that knows how to correctly program the board and parts)