I have a MacBook Air (April 2013) and a new Apple TV.
Mirroring of the desktop is alright if I disable my TV's post-processing of the image.
But If I start a video (VLC or Netflix for example), the quality is not very good. The framerate is too low and the sound is out of synch.
If I use the App Beamer, the image quality is great. Running Netflix natively on Apple TV works also great. My guess is, that Beamer streams the video file directly to Apple TV and that mirroring is slower, because the MacBook has to encode the image on the fly. Hence the low frame rate and delay (the video is also much smoother if I change the resolution down to 720p, but still not watchable for a movie).
Right now the situation is ok, because I can watch Netflix natively and stream files via Beamer. But this is not what I expected from Apple TV.
I didn't expect to play the newest action games like this, but stream videos to it in decent quality (YouTube, IMDb etc.) without using some native App on Apple TV.
Can I somehow improve this? Am I right that the bottleneck is the encoding of the MacBook? Can I improve this by disabling the MacBooks monitor or something?
EDIT:
An employee at an Apple certified store told me this is definitely my router. My housemate bought a TimeCapsule. This did not help a bit. I already guessed that the employee just didn't want to admit he sold me something I didn't want. I'll probably sell AppleTV now, but I'd still be interested in answers though.
Best Answer
I'm having quite the same issue not with an apple tv but with another stuff provided by my Internet broadband which is doing air mirroring. I have a mid 2013 macbook air and mirroring my screen is lagy.
So I thought the issue was from the router too, but my brother with his latest MacBook Pro doesn't have any lag, it's really fluid.
So I thought the MBA wasn't power enough too handle the real time encoding, but one day while I was mirroring my screen I launched a slide show in iphoto and it was really fluid. Then I noticed when I turn air mirroring on it's always lagy until I launch a video from QuickTime.
So, to sum up - this likely is a software issue since under iPhoto and Quicktime, the MBA is fast enough to handle high performance mirroring of some content. (Or that it lags when it has to both assemble the image to draw on the screen and then mirror it - but when QuickTime or iPhoto take over the entire screen - mirroring can be quite snappy).