There’s even a spec for inhibition http://people.freedesktop.org/~hadess/idle-inhibition-spec/
What window manager are you using?
Compiz, standalone.
I'm using xfce4-power-manager for dimming the screen (brightness to 20% after 90 seconds of inactivity, though not on external displays), and DPMS for standby after 3 minutes.
That spec is almost empty, and I'm not sure that would inhibit DPMS when configured through Xorg.
you’re welcome to give hadess feedback, his email is at the top…
Even if the spec is almost empty, without actual implementations, it's useless. Even if it were completed, and steam implemented it, DPMS still won't be disabled, because Xorg does not implement the other side of the spec.
Nothing extracted yet.
When running steam in big picture mode, the screen blaking is not inhibited.
My PC is configured to turn off the screen after 3 minutes of inactivity. Steam does not inhibit this, and since I'm not using my keyboard or mouse (I use my gamepad in big picture mode), the screen gets turned off.
The same seems to apply when seeing a video.
The simplest way to inhibit this is sending fake X events (a CTRL keypress when the users moves around with the gamepad sufices) and when playing a video.
I'm not sure how video players (eg: vlc) deal with this though.