Service Discovery
AirPlay does not require any configuration to be able to find compatible devices on the network, thanks to [DNS-based service discovery], based on [Multicast DNS], aka Bonjour.
An AirPlay device such as the Apple TV publishes two services. The first one is the Airplay for photo and video and in later versions also audio content and the other one is [RAOP], used for audio streaming and in later versions superseded by Airplay service.
_airplay._tcp
name: Apple TV
type: _airplay._tcp
port: 7000
txt:
deviceid=58:55:CA:1A:E2:88
features=0x39f7
model=AppleTV2,1
srcvers=130.14
The following fields are available in the TXT record:
| name | type | description |
|---|---|---|
| model | string | device model |
| manufacturer | string | device manufacturer |
| serialNumber | string | device serial number |
| fv | string | device firmware version |
| osvers | string | device OS version |
| deviceid | string | Device ID. Usually MAC address of the device |
| features | 32 bit hex number,optional high order 32 bit hex number | bitfield of supported features. This was originally a 32 bit value but it has since been expanded to a 64 bit value. To support both these types the mDNS value is encoded as two 32 bit values separated by comma with the comma and second 32 bit value being optional. |
| pw | boolean | server is password protected |
| acl | int64 | Access control level |
| srcvers | string | airplay version |
| flags | 20 bit hex number | bitfield of status flags |
| pk | hex string | public key |
| pi | UUID string | group_id / PublicCUAirPlayPairingIdentifier |
| psi | UUID string | PublicCUSystemPairingIdentifier |
| gid | UUID string | group UUID |
| gcgl | boolean | group contains group leader / Group contains discoverable leader |
| igl | boolean | is group leader |
| gpn | string | group public name |
| hgid | UUID string | home group UUID |
| hmid | string | household ID |
| pgcgl | boolean | parent group contains discoverable leader |
| pgid | UUID string | parent group UUID |
| tsid | UUID string | 3008B5C8-9BD3-4479-A564-90BFB3D780C0 |
| rsf | 64 bit hex number | required sender features |
| protovers | string | protocol version |
| vv | ? | vodka version |
_raop._tcp
name: 5855CA1AE288@Apple TV
type: _raop._tcp
port: 49152
txt:
txtvers=1
ch=2
cn=0,1,2,3
da=true
et=0,3,5
md=0,1,2
pw=false
sv=false
sr=44100
ss=16
tp=UDP
vn=65537
vs=130.14
am=AppleTV2,1
sf=0x4
The name is formed using the MAC address of the device and the name of the remote speaker which will be shown by the clients.
The following fields appear in the TXT record:
| name | value | description |
|---|---|---|
| txtvers | 1 | TXT record version 1 |
| ch | 2 | audio channels: stereo |
| cn | 0,1,2,3 | audio codecs |
| et | 0,3,5 | supported encryption types |
| md | 0,1,2 | supported metadata types |
| pw | false | does the speaker require a password? |
| sr | 44100 | audio sample rate: 44100 Hz |
| ss | 16 | audio sample size: 16-bit |
| tp | UDP | supported transport: TCP or UDP |
| vs | 130.14 | server version 130.14 |
| am | AppleTV2,1 | device model |
Audio codecs
| cn | description |
|---|---|
| 0 | PCM |
| 1 | Apple Lossless (ALAC) |
| 2 | AAC |
| 3 | AAC ELD (Enhanced Low Delay) |
Encryption/Authentication Types
| et | description |
|---|---|
| 0 | no encryption |
| 1 | RSA (AirPort Express) |
| 3 | FairPlay |
| 4 | MFiSAP (3rd-party devices) |
| 5 | FairPlay SAPv2.5 |
Metadata Types
| md | bit | description |
|---|---|---|
| 0 | 17 | text |
| 1 | 15 | artwork |
| 2 | 16 | progress |
| 50 | bplist |
Subtype
AppleTV = deviceModel has prefix “AppleTV”
HomePod = deviceModel has prefix “AudioAccessory”
ThirdPartySpeaker = HasUnifiedAdvertiserInfo or SupportsUnifiedPairSetupAndMFi feature is set
Unknown = otherwise
CanBeRemoteControlled
SupportsBufferedAudio is set and PINRequired is not set
State Changes
Depending on the state of the device the mDNS record is changed to reflect
this. Primarily it is the flags, gid, igl, gcgl, pgid and pgcgl
fields that are changed.
Apple TV not playing
flags=0x10644
gid=712F0759-5D44-41E7-AB67-FAB0AD39E165
igl=1
gcgl=1
Apple TV receiving AirPlay audio
flags=0x30e44
gid=19F5D4B2-8A06-4792-923E-8AFA83913238
igl=0
gcgl=0
pgid=19F5D4B2-8A06-4792-923E-8AFA83913238
pgcgl=0
Apple TV receiving AirPlay video
flags=0x30e44
gid=19F5D4B2-8A06-4792-923E-8AFA83913238
igl=0
gcgl=0
pgid=19F5D4B2-8A06-4792-923E-8AFA83913238
pgcgl=0
Apple TV receiving AirPlay screen
flags=0x30644
gid=712F0759-5D44-41E7-AB67-FAB0AD39E165
igl=1
gcgl=1
Apple TV playing local media
flags=0x10644
gid=FA69F5A2-5574-4E4D-A676-CA7F61A904A3
igl=1
gcgl=1