This happens on Nexus 7 2013 (Google stock 5.0.2) and also happens on Galaxy Note 12.2 tablet (Samsung stock 4.4.2). I am in a dark room. I have set the system brightness to the minimum (let us call this brightness MIN). To change brightness I use swiping up/down on the left screen area.

With MX Player, when the video starts playing, even the minimum brightness (which is 0) makes the screen brighter than MIN. There seems to be no way to set the brightness to MIN. I can clearly notice that the screen has been brightened, by pressing the home button or the task switch button. I can see that the screen remains bright for about 1 second then changes back to MIN.

With VLC, when the video starts playing, if its previous brightness was 0, the brightness does not change and remains MIN. But if I change brightness once, changing it to 0 does not lower the brightness to MIN. At this point, VLC acts just like MX Player.

Is this a bug of Android? It seems as if the system passes a false minimum brightness of the hardware to the software. Is this an intended behaviour to make video brighter? Anyways, is there any way to prevent this brightness change? This hurts my eyes when I watch videos in a dark room.

==PS==

This behaviour is also happening in CyanogenMod 12 (Android 5.0.2).