Apple launched the HomePod mini six years in the past, in 2020.
I am not one into sensible audio system, however the characteristic that made me take a more in-depth look was their skill to kind stereo pairs, with none direct wired connection.
I do know there are different speaker producers with wi-fi audio system, however to my information, Apple was simply utilizing AirPlay over WiFi… so how does it work?
Via the magic of shopping for two HomePods mini (pictured above), I discovered. A video detailing the method is embedded under:
Establishing a HomePod mini (no Macs allowed)
Earlier than exploring how Apple does the stereo pairing, I needed to arrange the audio system. Considering like a long-time Mac proprietor, I did the only factor and plugged the hard-wired USB-C cable straight into my Mac.
Nothing occurred.
Nicely, there was somewhat pulsing amber mild, however nothing else:
So I plugged it into the wall utilizing the USB-C energy adapter provided within the field, and it appeared as well as much as a white pulsing high—somewhat higher.
However I nonetheless could not join on my Mac. Not a promising begin, I used to be largely stunned I could not simply use it as a USB-C related speaker—or not less than as a Bluetooth speaker!
I browsed Apple’s documentation and finally discovered you may’t use a Mac to arrange HomePods:
You want an iPhone or iPad to arrange HomePod. You may’t arrange HomePod with a Mac.
How dumb is that?
I pulled out my iPhone, and realized I needed to connect my Apple account to the HomePods, and conform to a bunch of issues simply to get them to start out working as audio system. Would not appear very sensible to me.
Looking for PTP over WiFi with Wireshark
A viewer of my YouTube channel messaged me (and for the lifetime of me, I am unable to keep in mind who it was, or what platform he messaged me on) and hinted that Apple is likely to be utilizing a type of PTP for his or her HomePod minis, so I believed I would play some audio and hear in with Wireshark.
I attempted to allow Monitor mode on my Mac Studio’s WiFi connection, however I wasn’t in a position to get any packets that method. It really works on wired Ethernet, however not WiFi. Most likely some safety subject in macOS 26 Tahoe.
Replace: One among this weblog’s readers emailed me and stated Wireshark can present the reside site visitors in case you disassociate with the present WiFi community earlier than starting Monitor mode.
I did that (simply click on on the related community within the WiFi menu to disconnect, whereas leaving WiFi on), checked the ‘Monitor’ checkbox in Wireshark’s choices for the WiFi connection (en1 on my Mac Studio), and may verify you may monitor that method. Good!
Fortunately, Apple features a ‘Wi-fi Diagnostics’ app on fashionable Macs which has a in-built Sniffer device, which sniffs all site visitors given a Channel and Width setting.
The app is positioned in /System/Library/CoreServices/Purposes alongside different gems like DVD Participant and About This Mac. Open it, then earlier than clicking something within the diagnostics wizard that seems, click on the Window menu and select “Sniffer”:
I made certain my Mac was related to the identical WiFi community (a 5 GHz WiFi community), and the defaults have been chosen for me (Channel 100, Width 80 MHz).
I clicked ‘Begin’, and performed again some audio from one other Mac to the audio system. After about 10 seconds, I clicked ‘Cease’. This generates a .pcap file inside /var/tmp, so I copied that out into my Downloads folder, and opened it with Wireshark.
Searching the packets, I shortly discovered what I used to be in search of: a number of units of 4 PTPv2 packets:
SyncFollow_UpDelay_ReqDelay_Resp
These 4 packets are what PTP (Precision Time Protocol) makes use of to sychronize time between two computer systems.
And on this case, the packets are wrapped up in a peer-to-peer connection between the audio system and my Mac, utilizing Apple Wi-fi Direct Hyperlink, which is used for AirPlay, AirDrop, GameKit, and different high-speed direct connections.
Operating by AWDL or over WiFi, PTP can use software-based timing to sync clocks on a number of HomePods to inside a microsecond or so—adequate for A/V sync. And the requirements they appear to be utilizing are gPTP and IEEE 802.1AS, as a part of the AVB (Audio Video Bridging) normal.
Apple utilizing requirements: gPTP and AVB
gPTP and AVB are new to me.
Apple adopted the 2011 model of the 802.1AS normal for AirPlay 2 to ensure audio stays (nearly) completely in sync between a number of audio system. It appears to even be what’s used to sync the sound popping out of HomePods with video displayed on Macs, iPhones, iPads, and Apple TVs.
If all of your units have microsecond-accurate timing, frames on the show can sync as much as a number of unbiased audio units on the right audio time, and you do not have both bizarre section points, or A/V de-sync that was much more prevalent a decade in the past (and nonetheless occurs far too usually right now).
This Aud-iOS weblog put up on Networked Audio on macOS has a whole lot of attention-grabbing context, however it’s too dangerous the HomePods do not work as a typical ‘Community AVB system’, which looks as if it might be extra appropriate with different audio ecosystems.
To play again audio to AirPlay 2 units from Linux, you must use one thing like owntone-server or airplay2-rs—the latter explores how Apple’s utilizing gPTP in AirPlay. AirPlay (the primary model) appears to have used NTP, however that may end up in just a few milliseconds of error—perceptible to the human ear.
I had speculated about how Apple handles audio with skilled gear utilizing Dante, Livewire, Ravenna, AES67, and so on., and it seems to be like their AVB and gPTP system handles all that—however Apple appears to be content material with microsecond-level sync.
Getting significantly better than 1 µs sync requires {hardware} PTP timestamping (or for WiFi, newer tech like FTM, or Nice Timing Measurement), and I have never seen any solution to get that on a Mac, not less than not in any public documentation.
