Do I need an ethernet cable to stream apple tv

The chap at the Apple Store is wrong.

You can use ethernet or wi-fi.

If your wi-fi is good and free from interference it'll work fine - if you have poor signal and frequent disconnections with existing wi-fi devices AppleTV might suffer the same problems.

You could always look to getting some powerline network adapters if wi-fi wasn't good and didn't want a long cable from the router.

AC

You can connect through Wi-Fi. A wired connection is often more reliable for video streaming since things like cordless phones, baby monitors and microwave ovens can interfere with the Wi-Fi signal, but not required. So if your get problems where the content stutters or pauses a lot, then you may have to move your router and AppleTV around. (And the cordless phone or whatever.) I recall reading a lot of recommendations to use a wired connection for Netflix. I happen to have wired my DVD player (with built-in Netflix) and it gets much less pausing. But I also have a couple of cordless phones directly in-line with the router and the microwave is nearby. But otherwise, if you have a strong Wi-Fi signal, it is possible to use Apple TV with Wi-Fi, particularly if you're going to stream audio only.

If all else fails, then you might have to consider running a wire. But I'd say try it first. Just be prepared to move the phone and things around for a few days if you need to tweak the Wi-Fi. Good luck!

Hope it works well - let us know how you get on.

AC