Version 5 SPS: lossless support

[CarlBernard]

Hi Mike,
I read about the new version 5.
Here's my question:
If I use my HomePod or Apple TV 4K and stream Apple Music Lossless to my RPI 3 with SPS 5, what will SPS 5 receive?
Lossy AAC 256 (buffered audio) or Lossless (buffered or real-time audio?) ALAC 16/44, 24/48?
I'm still using the previous version right now.

FYI, in this forum, a user verified that with an apple tv 4k 3 gen if he sends the audio (NO Apple Music) of a video to SPS it is lossless:
https://community.firecore.com/t/44-1-khz-audio-output-tvos-17-2022-atv4k-3rd-gen/45307/17

[mikebrady]

Thanks for the interesting information.

The situation I'm describing below is with an Apple Home setup based on a HomePod mini ("HPM") and an Apple TV 4K ("ATV"). The "owner" of the home's Apple Music account is the source for music played by the HPM and the ATV. "Audio Lossless" and "Dolby Atmos" are both enabled in the owner's Apple Music settings in the Apple Home's settings.

The Shairport Sync 5.1 devices have default settings except for specifying ALSA output DACs and mixer controls. BTW, that means that the DACs will dynamically change frame rates (e.g. 44.1k to 48k) and channel settings (e.g. stereo to 5.1 or 7.1) to best accommodate the incoming audio.

If you play music on the HPM using the Apple Home app, or if you play music on the ATV using the ATV's Music app, then when you AirPlay from them to an SPS v5.0 or later device, they will play as follows:

Source	Output Format
Realtime	ALAC/S16/44.1k/2
Buffered	AAC/F24/48k/2 (Default -- i.e. if the source is not Lossless or Dolby Atmos)
Dolby Atmos	AAC/F24/48k/5.1 or AAC/F24/48k/7.1
Lossless, Hi Res Lossless	ALAC/S24/48k/2

Where ALAC is Apple Lossless, S24 is Signed 24-bit integer, S16 is Signed 16-bit integer, F24 is 24-bit Floating point, 44.1k is 44,100 frames per seconds, 48k is 48,000 frames per second, 2 is stereo, 5.1 and 7.1 are surround sound formats.

A few things to note:

1. The music has to originate with the HPM or ATV to come through as lossless or surround. For example, if you play audio from an iPhone to the HPM and to SPS at the same time -- that is, if the music source is the iPhone rather than the HPM -- then the format will be AAC/F24/48k/2.
2. The HPM/ATV will output the same audio format to all connected devices. That means that if another connected device can't receive Lossless or Dolby Atmos, then your SPS device, connected to the same source, will only get lossy audio, typically AAC/S16/44.1k/2.
3. If you use the Home app settings to toggle Dolby Atmos and/or Lossless while audio is playing, the stream will dynamically change format, though it may take a little time. There is usually a short gap while the changeover occurs, and the gap seems to be intrinsic to the contents of the stream feed rather than a fault in SPS.
4. SPS will automatically downmix, e.g. from 5.1 to stereo, if you don't have enough output channels on your output device. That seems to be what's happening in the report you quote above.
5. From the report, it does look as if the older, non-4K, ATV does not provide Dolby Atmos, and possibly not Lossless either.

[mikebrady]

Yeah, that's my belief. Of course, we don't have easy access to S24/48k source, so we can't check bit for bit, but I have no reason to doubt that we are getting lossless 48K 24-bit stereo, which is great.

There is a slightly related discussion here.

[CarlBernard]

Mike,

You're my idol!
I've been waiting for this news for a long time.
As soon as I can get my hands on the terminal, I'll install SPS 5 and update you.

Will it work with all Apple TV 4Ks (1st, 2nd, or 3rd generation)?
I'll try it on a 2nd generation ATV.

Thank you very much.

[mikebrady]

Great! For sure it works with an Apple TV 4K Second Generation (A2169) 64G.

[CarlBernard]

Hi Mike,

I tried your new system and everything works great as usual.
Thank you and congratulations.
I tried both the Apple TV 4K Gen 2 (ATV) and the HomePod mini (HP).
Both send streaming data in ALAC 24/48 format to your shairport-sync (SPS), and SPS sends the same format it receives to output device.
However, I don't understand why Apple insists on always sending the same 24/48 format to SPS even though the original format they receive from Apple servers is different.
Many tracks received by ATV and HP are in CD 16/44 or 24/44 format.
I'm not too concerned about the 16-bit to 24-bit conversion, as it's just adding zeros, but I'm more concerned about the 44 kHz to 48 kHz conversion, although I hope the APT and HP devices do it well.

Regarding the new version of SPS 5.0, how did you manage to "capture" the lossless format sent by ATV or HP via AirPlay 2?
Has Apple decided to "officially" send these formats via AirPlay 2 if the source is ATV or HP?
If I use an old Airport Express with AP 2, will it receive the same format from these devices, or have you managed to make this "magic" available to a select group of crazy IT audiophiles?!?
If, in the future, Apple decides to also send streams in the original format (16/44, 24/44 [24/48 OK!] and beyond... 24/88, 24/96, 24/192), would your current SPS be able to receive it correctly, or would you have to rework the software?

I haven't been able to test the new system with Tidal and Qobuz.
I'll update you as soon as I can.
Who knows, maybe they send the same format they receive?!?

Thank you and have a good evening!

[mikebrady]

It's good to hear that it's working for you, and I hope you enjoy it. To my ear, the difference is subtle but real. It's especially noticeable to me with bright percussion, e.g. the sound of high-hats.

I don't understand why Apple insists on always sending the same 24/48 format to SPS even though the original format they receive from Apple servers is different. Many tracks received by ATV and HP are in CD 16/44 or 24/44 format. I'm not too concerned about the 16-bit to 24-bit conversion, as it's just adding zeros, but I'm more concerned about the 44 kHz to 48 kHz conversion, although I hope the APT and HP devices do it well.

So, to be completely precise, we only know that the transmission from ATV/HPm is S24/48k/ALAC. We don't really know for sure how the original source is encoded or what is sent from the servers to the ATV/HPm. For all we know, Apple may have very high resolution originals (e.g. F32/192k/Lossless or something) and resample them, losslessly, to the desired format. We don't even know where that occurs -- is it at the server end or at the ATV/HPm end?

Even if you have uploaded a CD in S16/44.1k/ALAC, we have no assurance that it is stored in that way. If the CD is a commercial one, it may be that Apple has a different version of it with different encodings.

If you upload a non-commercial CD, I understand that you get an 256kb/s F24/48k/AAC or F24/44.1k/AAC version of it on playback.

Edited To Add The significance of the Audio Quality Settings -- S16/44.1k/ALAC being displayed -- is a mystery. Perhaps that format is being transmitted from Apple, but if so, we haven't found it on AirPlay. We know that it can appear on an iPhone even when what is sent out on AirPlay is F24/48k/AAC. It kind-of suggests that the transcoding may be happening in the device itself. But this is conjecture.

Regarding the new version of SPS 5.0, how did you manage to "capture" the lossless format sent by ATV or HP via AirPlay 2? Has Apple decided to "officially" send these formats via AirPlay 2 if the source is ATV or HP?

We don't know what Apple is doing in this space. It looks as if they have soft-launched S24/48k/ALAC and Dolby Atmos AirPlay 2 from ATV and HPs, and are gradually getting the bugs out of the service. But again, that is just conjecture on my part.

If I use an old Airport Express with AP 2, will it receive the same format from these devices, or have you managed to make this "magic" available to a select group of crazy IT audiophiles?!?

Unfortunately, I don't think so, unless they update the firmware. It seems that the APX advertises its features, and they seem to limit to AAC/44.1k/F24. What's more, if you connect an ATV/HPm to an APX and an SPS device, the SPS device will receive only AAC/44.1k/F24, the same format as the APX.

If, in the future, Apple decides to also send streams in the original format (16/44, 24/44 [24/48 OK!] and beyond... 24/88, 24/96, 24/192), would your current SPS be able to receive it correctly, or would you have to rework the software?

It depends. If they just add extra formats, then SPS would have to be adjusted to accommodate them, although it shouldn't be too much work as long as FFmpeg can decode them. But if they, for example, encipher the audio in some other way, then we would be stuck.