A way to find out if an AirPlay audio device is used, password protection of CoreAudio methods

Question

I am currently having problems with my AirPlay device inside my application. I used this theme as a model for setting up a broadcast device. But at present, it was not possible to find a solution for two problems:

First of all, I could not determine if the broadcast device is busy or not, because it does not support simultaneous input? I tried to find any property inside CoreAudio, but with no luck.

The second problem that I learned about was related to the broadcast device with the password turned on. I can’t get a notification if a password has been entered or not, as a result, my application cannot respond in the same way as to any of these events.

Thanks in advance for your help.

Answer 1

I am not familiar with the new CoreAudio APIs, so it can be a lot easier. This is how I solved the same problem last year.

You can determine if the device requires a password with Bonjour (also called multicast DNS or Zeroconf). You should be able to match the source name with CoreAudio information. For AirPlay audio, you need to check _raop._tcp devices. Here's how it works with the terminal:

Open AirPlay apps first (note that the dns-sd command is called mDNS before Mountain Lion):

  laurent ~ $ dns-sd -B _raop._tcp
 Browsing for _raop._tcp
 DATE: --- Tue 15 Jan 2013 ---
 17: 37: 31.977 ... STARTING ...
 Timestamp A / R Flags if Domain Service Type Instance Name
 17: 37: 31.977 Add 2 4 local.  _raop._tcp.  406C8F53F1DD@iMac de Laurent

Then record the full record of the AirPlay instance:

  laurent ~ $ dns-sd -L " 406C8F53F1DD@iMac de Laurent" _raop._tcp local
 Lookup 406C8F53F1DD@iMac de Laurent._raop._tcp.local
 DATE: --- Tue 15 Jan 2013 ---
 17: 43: 47.097 ... STARTING ...
 17: 43: 47.098 406C8F53F1DD@iMac \ 032de \ 032Laurent._raop._tcp.local.  can be reached at iMac-de-Laurent.local.►000 (interface 4)
  et = 0,1 ek = 1 ss = 16 raAudioFormats = ALAC, L16 tp = UDP pw = false txtvers = 1 ramach = iMac12,1 vn = 3 md = 0,1,2 sv = false sm = false ch = 2 sr = 44100 rast = afs rastx = iafs cn = 0.1

pw=false indicates that there is no password. This is the main idea, now you should do the same with DNSServiceResolve .

Now, the only way to check if a device that I know about is busy is to actually connect to it. Internally, AirPlay uses RTSP, so you can send this request:

  RTSP / 1.0 OPTIONS *
 # empty line

If the device responds with a status of 453, it means that it is already streaming.

You can check my AirPlay RTSP stack for more information.