iPad AirPlay to Apple TV - 802.11n problems I have been attempting to resolve an issue with AirPlay from an iPad to AppleTV.  Here are the details:

Playing media (audio or video) originating on the iPad sent to
AppleTV via AirPlay does not work.


With audio-only media, the result is mostly silence with
occasional very short bursts (less than 100ms) of sound.
With video, the video does not play at all. The TV display can be
one of


black screen with a rotating spinner in the center
black screen with the blue time bar at the bottom and a
rotating spinner at the bottom left
white screen with the blue time bar at the bottom and a
rotating spinner at the bottom left



The failure mode is extremely specific, and requires:


The media being played resides physically on the iPad. Media of
any type being streamed from the Internet via the iPad does not
have this problem.
The problem occurs only when both the iPad and AppleTV are on the
same 5GHz network. Any other combination with either the iPad or
AppleTV or both on the 2.4GHz network operates correctly.


Hardware:

iPad       mdl:MC979LL    iOS:5.1.1
AppleTV    mdl:MD199LL/A  OS:5.1.1(5433)
Router     Netgear WNDR3400V2 with firmware V1.0.0.34_1.0.52

The router is running in access-point mode where it does not do any
routing, just provides wireless access.

During testing I tried the following:


Changing WiFi channels
Upgrading the router firmware to the latest version
Rebooting and power-cycling all equipment multiple times,
including hard-resetting the iPad
Testing with iTunes on the PC not running, in case it is somehow
saturating the connection to the AppleTV
"Reset Network Settings" on the iPad.


So far no luck. 

BTW, I wanted to tag this post 802.11n but that tag does not exist and I can't create it with less than 300 rep.  Would somebody please create that tag, add it here and delete this paragraph? Thx.
I was poking around in the router's admin interface and examined the wireless
settings.  On this particular router, for each frequency band (2.4GHz
and 5GHz) there is a "Wireless Mode" setting that enables high-speed
operation. It has three settings for the 5GHz network:

Up to 54Mbps
Up to 145Mbps
Up to 300Mbps


The factory default is Up to 300Mbps.  I tested all three settings, 
and the only one that works is the slowest Up to 54Mbps.

It appears that AppleTV's 802.11n implementation does not support 
speeds above 54Mbps.