Resolved Display sleep / screen saver not activating with P2715Q 4k monitor

[kazibole]

I have a Mid-2014 15" Macbook Pro w/ Intel Iris graphics running El Capitan 10.11.2. With my old 1080p monitor attached via a Mini DisplayPort to DVI cable, the screen saver and display sleep options (in System Preferences -> Energy Saver) work as expected. However when I replace the monitor with a Dell P2715Q 4k monitor attached via a Mini DisplayPort to DisplayPort cable, the monitor stays on forever and both the screen saver and display sleep options never activate. I can manually put the display to sleep via the keyboard shortcut Control-Shift-Eject. I have tried with both the monitor being detected as "Television: Yes" and with the Force RGB mode patch.

Any ideas on how to resolve this?

 

[kazibole]

I have figured it out. The screensaver or display sleep will not activate when audio is playing through the DisplayPort connection. What caused the problem even with no audio was playing was that I had installed Sound Siphon to allow me to control the volume of the digital output. I guess this application (and similar ones) will always have the audio channel open. Once I uninstalled (or turned off) Sound Siphon, the problem went away.