Resolving AirPlayXPCHelper Perr NULL kCanceledErr with Apple TV and MacOS

I decided to finally get an Apple TV so that I could use my iPad and MacBook Pro to airplay to my projector. So far I’ve been really impressed by it and how well it works with modern amplifiers and my iPad.

Sadly though, when I tried to use my MacBook pro to airplay to the Apple TV I recieved an “Unable to connect” error, with no further description.

Initial Research

The first step was to look in console.app at the local system logs. The following item stood out:

error 09:24:41.459722+1000 AirPlayXPCHelper ### Error: CID 0xACF10006, Peer NULL, -6723/0xFFFFE5BD kCanceledErr

I only found a single result on a search for this, and they resolved the problem by disabling their MacOS firewall - attempting this myself did not fix the issue. There are also reports of apple service staff disabling the firewall to resolve airplay problems too.

Time to Dig Further …

Now it was time to look more. To debug an Apple TV you need to connect a USB-C cable to it’s service port on the rear of the device, while you connect this to a Mac on the other side. Console.app will then show you the streamed logs from the device.

While looking on the Apple TV I noticed the following log item:

[AirPlay] ### [0x8F37] Set up session 16845584210140482044 with [<ipv6 address>:3378]:52762 failed: 61/0x3D ECONNREFUSED {
"timingProtocol" : "NTP",
"osName" : "Mac OS X",
...
"isScreenMirroringSession" : true,
"osVersion" : "10.15.4",
"timingPort" : 64880,
...
}

I have trimmed this log, as most details don’t matter. What is important is that it looks like the Apple TV is attempting to back-connect to the MacBook Pro, which has a connection refused. From iOS it appears that the video/timing channel is initiated from the iOS device, so no back-connection is required, but for AirPlay to work from the MacBook Pro to the Apple TV, the Apple TV must be able to connect back on high ports with new UDP/TCP sessions for NTP to synchronise clocks.

My Network

My MacBook pro is on a seperate VLAN to my Apple TV for security reasons, mainly because I don’t want most devices to access management consoles of various software that I have installed. I have used the Avahi reflector on my USG to enable cross VLAN discovery. This would appear to be issue, is that my firewall is not allowing the NTP traffic back to my MacBook pro.

To resolve this I allowed some high ports from the Apple TV to connect back to the VLAN my MacBook Pro is on, and I allowed built-in software to recieve connections.

Once this was done, I was able to AirPlay across VLANs to my Apple TV!