Add version-based visibility of shairport-sync endpoints

[kuzhylol]

This patch introduces modification to AirPlay attributes allowing AirPlay clients seeing only appropriate Endpoints of specific version of AirPlay protocol.

[Test]
Run two instances of shairport-sync - built for version 1 and for version 2.

TuneBlade recognizes only AirPlay version 1 instance running.
MacOS/iOS recognizes only AirPlay version 2 instance running.

Without that patch, both MacOS/iOS detect two endpoints at the same time. The TuneBlade detects only AirPlay version 1 since it doesn't support AirPlay version 2.

[mikebrady]

Very interesting, thanks. Let me run a few checks.

[kuzhylol]

Hi @mikebrady, do you have any thoughts or concerns?

[mikebrady]

Apologies, Oleh -- I haven't yet run my checks; very busy IRL just now.

[mikebrady]

Thanks again for this interesting PR, which I have tested out and which seems to work.

If you could make this target the development branch, rather than the master branch, if would be much preferred. This way, it can be further tested by advanced users before it becomes part of a full release.

[kuzhylol]

Hi @mikebrady,
Thank you for testing my patch.

I've moved the target branch to development.

[mikebrady]

Thanks for this. Let's give it a try!

[mikebrady]

Hi @kuzhylol. It looks as if @poker335 is right, so an update has been pushed on the development branch with these changes reverted.

Thanks -- it was a nice idea, but unfortunately it doesn't seem to be a general solution. When you look at the Unofficial AirPlay Specification, in the section on "Audio codecs" it looks as if the strings removed specify the codecs used, and in that sense, removing them seems the wrong thing to do.

[kuzhylol]

Hi @mikebrady, this is very unfortunate. Based on you experience, why removing "Audio codecs" section can split APv1 and APv2?

Perhaps you could propose more general solution?
What if we remove this section only for APv2?

[mikebrady]

Hi @mikebrady, this is very unfortunate. Based on you experience, why removing "Audio codecs" section can split APv1 and APv2?

Hi @kuzhylol. Since AirPlay specifications and protocols have not been published, we can only go by our experience and "common sense", which is always a bit unreliable. On a "common sense" basis, it looks like removing the advertisement of the audio codecs seems not to be very sensible. This seems to be confirmed by @poker335's experience, and my own, using Shairport Sync on real Apple sources.

Perhaps you could propose more general solution? What if we remove this section only for APv2?

This is not something I've spent a great deal of time considering, but, in the absence of documentation to guide us, any changes would have to be very thoroughly tested.

[kuzhylol]

Hi @mikebrady, I've been thinking about the 'issue" happened on #1856

Isn't that an expected behavior to have AirPlay v1 not visible for AirPlay v2 "only" device?
The iOS 17.5 and iPadOS 17.5 looks a cutting edge firmware version. Why Airplay v1 is even needed there?

Having AirPlay v2 only for brand new devices -- That's what I actually wanted to improve in Shairport Sync 😄
This case just confirmed that patch works.

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What do you think on that @mikebrady?

[mikebrady]

Thanks for your comments.

Isn't that an expected behavior to have AirPlay v1 not visible for AirPlay v2 "only" device?

AirPlay 2 devices are capable of classic AirPlay operation for compatibility with classic AirPlay devices. AirPlay 2 devices also need to be able to switch dynamically from AirPlay 2 to classic AirPlay operation.

The iOS 17.5 and iPadOS 17.5 looks a cutting edge firmware version. Why Airplay v1 is even needed there?

Apple continues to support classic AirPlay on these systems.

Having AirPlay v2 only for brand new devices -- That's what I actually wanted to improve in Shairport Sync 😄
This case just confirmed that patch works.

Classic AirPlay is supported by Apple on brand new devices, and it remains, for the present at least, the only lossless AirPlay. It would be a step backwards for Shairport Sync to drop support for Classic AirPlay on newer operating systems.

Generally, it looks as if Apple is careful to retain classic AirPlay compatibility years after AirPlay 2 was introduced and classic-AirPlay-only devices were discontinued. This may be because audio devices -- e.g. stereos and AV receivers -- have a much longer expected lifetime than computer-based products. It seems only logical that Shairport Sync should try to do the same thing.