Why is local video streaming to Apple TV jerky?

Have you tried connecting Apple TV via ethernet?

To see a status of your network go to istumbler or similar, this will give an accurate representation of signal strength along with noise any nearby networks

How old is the main router? Is it up to date? What are the results of the report? Test on another network

This would indicate an issue with the local network, the online services mentioned adapt to the connection anyway. If you are mirroring from the Mac that will require more resources from the network (so you should also make sure to cease other activity like streaming, network backups etc)

If you are referring to the Extreme, the last generation was released 4 years ago. While not always the case routers are more prone to issues after 3-4 years, that would impact performance over ethernet as well.

You can also verify network performance by testing on another network, preferably a controlled one like Apple's

I'm using the newest AirPort Express (with actually firmware) and the newest Apple TV (with actually firmware) and video streaming is so poor. Just Beamer player is doing this best... but anyone knows why the there is a problem with streaming directly from macbook pro retina (late2012) dashboard do my Apple TV?

Mirroring requires more from the network. See above

I've seen this both with my iPad and with my Macbook Pro. What I noticed in many cases is that a reboot of either device seems to help clear this up. I use the Dishanywhere site to stream my satellite programming to my kitchen TV which is tied to my Apple TV. I assume that enough garbage is sometime left running in the background that this devices are sometimes sapped to provide the steady video stream necessary.

The reason in most cases is the network, which would require troubleshooting. You are welcome to have it tested at Apple to verify.

Seems that if it's network related, this is going to be a hard nut to crack. I assume you can bring your Airport Extreme in to be checked out, but if you are using another brand of wireless router, you won't get much help there. I know wireless interference can play havoc with signals and one of the things I'd check out with some sniffer software is that possibility. Just sitting here in my kitchen I can see signals from 15 different wireless routers in my neighborhood. Using 2.4 GHz channel selection can make all the difference between good and poor performance. Granted those 15 access points in many cases aren't close enough to interfere, a couple are and I've seen performance on my Macbook Pro suck sometime because a close by wireless router pops onto or close to the same channel I'm on. That's a lot why I bought an Airport Extreme and use the 5 GHz side as much as possible. In the case of my Apple TV and all my Apple devices, I run on the 5GHz side. Signal strength is good and when I get the slow downs when using Airplay, the reboots of the streaming devices usually resolve the issues.

I wasn't blaming your wireless network, in your case it could be an issue with the router. There is a lot more strain on a network to mirror then simply stream online video. Its working just fine here and for others as well. I suggested to take it in for testing, so best to forward.

A router is still an electronic device, it can struggle with maintaining a connection as time goes on. It's not common, but it can happen. It could also be a setting or undue strain on the network caused by other activity (mirroring requires full resources). These are networking devices, and they are working just fine for the majority. The difference would be the network setup. If you want to rule it out then test it at Apple