I tried different cables whith no success. Tried whith my old Linksysrouter and it worked perfekt as well.
Thankful for any new lead i could get!

I have the same model, my first MikroTik and it's blown me away except for this seriously annoying problem.Tried whith my old Linksysrouter and it worked perfekt as well.
Thankful for any new lead i could get!
/interface wireless> set 0 multicast-helper=full
Did you try setting the multicast-helper option as I posted directly above your reply?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?
The issue is (was) specifically with excessive buffering when attempting to AirPlay YouTube to an AppleTV; after starting the connection it would take up to a minute for the video to start playing.Not sure what problems folks are having. I have the RB450G that connects two Apple TV's...Apple TV1 and Apple TV3 via a gigabit switch and cat7 Ethernet cables for two years...streaming Netflix, never a problem.
Yes, multicast-helper=full.Did you try setting the multicast-helper option as I posted directly above your reply?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?
Yes, and the YouTube AirPlay (multicast) traffic from your iOS device lands on the wlan interface of the MikroTik before getting shuttled over the bridge internally and spit out the LAN.But i am using Ethernet connection between PC and ATV3.
Quoting myself since it looks like you're dealing with a different issue if you're pushing content from iTunes on a PC to the AppleTV, you're having issues with audio, or?Yes, and the YouTube AirPlay (multicast) traffic from your iOS device lands on the wlan interface of the MikroTik before getting shuttled over the bridge internally and spit out the LAN.But i am using Ethernet connection between PC and ATV3.
The issue is multicast propagation between wireless and wired, even when they're on the same bridge.
I was going to lab it up and to packet capture but since the multicast-helper option resolved the issue for me I didn't bother.
Sorry for late answer, was busy.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 100Mbps / Full Duplex rather than letting it auto negotiate.
No, I am trying to stream m4v file via iTunes HomeSharing using Gigabit LAN. And it freezing.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?
Wow...that is certainly strange. Is all devices Apple? In my case, all devices are Apple made (for the synergy)...my Mikrotik RB450G is my main router that subdivided into two networks...my personal and my guess. My personal network is control with an Apple Extreme in bridge mode...to which all Apple devices (laptop, desktop/server, and IOS) connected via a gigabit switch or WIFI. That way I take advantage of the Apple synergy of hardware and software.No, I am trying to stream m4v file via iTunes HomeSharing using Gigabit LAN. And it freezing.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?
If I playing file using Wi-Fi - it works fine.
Set muticast-helper to full on wlan interface, you need to do it via CLI or enable advanced options.I'm having the same problem. Did anyone figure this out?