sorry for my bad English but I try to describe my problem so good as I
can. If I look a video or live stream the screen is after 10 minutes
dark. Only chromecast is able to hold the screen open. Firefox or VLC
media player can't do this.
My desktop is mate and the window manager is lightdm and I found no
place where I can change this from 10 minutes to maybe 2 hours or longer.
I hope someone can help me. I think this must be a file under /etc or
something like that.

Greetings Frank