>> the video breaks in square artifacts like this for example
http://i.imgur.com/6ipQr.jpg which is annoying.
I have seen exactly the same breaking. It happens on my older PC when playing HQ videos with high bit-rates (1080P etc).
So basically VLC needs a bit more power to decode video.
I tried SMPlayer on my old PC and there's no break-up but it plays in slow-mo.
With mpv Media Player the video plays ok with no slow-down and no breaking-up even on my old PC.
I guess that is why mpv is the default program for mp4 files.