I wished that the xfce-power-manager would recognize when a video is playing (e.g. VLC, youtube in browser) or when running games where I am e.g. only spectating (so not user input, e.g. when watching a demo). If so, then xfce-power-manager should not blank/lock the screen. This is state-of-the-art in other OS (e.g. Windows, OS X) and shouldn't be missing on XFCE ? :) Thanks ! I am on Arch with XFCE btw.
This should be working now since 1.6.0. If the application calls 'inhibit' on the org.freedesktop.PowerManagement interface it will happen automatically, otherwise you can use the Presentation Mode in xfce4-power-manager to manually enable it. Depending on your screensaver, you may need to configure a command to inhibit it. /xfce4-power-manager/heartbeat-command is the xfconf property.
Marking this as fixed since we implement the official FreeDesktop method to achieve this. If specific programs don't make use of it, please contact the developers of these programs and have them fix their code to call the power management D-Bus interface