No, only Apple TV.
PC--glan--RB--glan--ATV = freezing
PC--glan--RB--glan--switch--glan--ATV = works fine
PC--glan--RB--802.11n--ATV = works fine

If understand correctly, you're trying to stream via airplay from an IOS device to your AppleTV...namely YouTube content...is there any reason you can't get the YouTube content directly from your AppleTV? No, I am trying to stream m4v file via iTunes HomeSharing using Gigabit LAN. And it freezing. ...

I don't have this setup, but since someone further up the chain mentioned that adding a hub/switch between the apple TV and the Mikrotik helped... have you looked at the link between the apple TV and the Tik? What is the port auto negotiated at? Is it flapping? Maybe try setting that port to 100Mbp...

I have issue with playing video (1080p)

I found temporary workaround! I have connected ATV to my Mikrotik via dumb unmanaged 5-port Gigabit switch (TP-Link). Problem has disappeared. Any ideas why? Did you try setting the multicast-helper option as I posted directly above your reply? Yes, multicast-helper=full. But i am using Ethernet co...

Found temporary solution: http://forum.mikrotik.com/viewtopic.php ... 30#p482530

I found temporary workaround!
I have connected ATV to my Mikrotik via dumb unmanaged 5-port Gigabit switch (TP-Link).
Problem has disappeared. Any ideas why?

My AppleTV is doing the same on RB951G. It works much better on WiFi and extremely slow on ethernet connection. All other devices are fine.
Did you find out how to fix that?

Do you solved problem with wired connection? I have the same issue with same router 951G-2HnD.

I have same trouble too. ATV3 connected directly to ethernet port 951G-2HnD, and when I try to play something from iTunes using Internet connection, or from my PC via iTunes Home Sharing, ATV begin buffering infinitely. But if i connect ATV to 951G-2HnD via wifi, everything works fine. Have changed ...