Sound from an Apple TV plugged in an LG monitor I'm hoping to plug an Apple TV 4th generation into an LG IPS277L (http://www.lg.com/hk_en/monitor/lg-IPS277L) which is equipped with the following input/output connections:


D-Sub:            Yes
HDMI:         Yes (HDMI 1, HDMI2/MHL)
Headphone Out:    Yes
Others:           MHL(Mobile)


Can I plug in an Apple TV 4 with an HDMI cable, and then (in order to get the sound from the Apple TV) plug external speakers in the headphone out connection from the monitor?
The answer is both Yes and No depending on the model. Let me explain.

The model you have linked to at http://www.lg.com/hk_en/monitor/lg-IPS277L is the Hong Kong model and this has a headphone socket. However, if you were buying the model from another country (let's use Australia as an example) it may not have the headphone socket: http://www.lg.com/au/it-monitors/lg-IPS277L-ips-monitor

The model you have linked to is now discontinued, but you can still access the manual downloads etc from: http://www.lg.com/hk_en/support/support-product/lg-IPS277L

If you download the manual it seems to confirm the headphone socket exists, but does not make any real mention of this anywhere. However, the same manual is used for both the LG IPS277L and the LG IPS237L (they are identical, one is basically the 24" model, the other the 27" model).

Now, if you happen to read the review on this page about the LG IPS237L, it is clear that for this particular model you can do exactly what you want to do. 

I suspect that as long as you have a Headphone port you will be right.