AAC-ELD support

[wasdwasd0105]

Hi,

The apple devices use AAC-ELD instead of AAC to stream to Airpods and it has a much better sound quality. So can the software stream using AAC-ELD?
I made a folk https://github.com/wasdwasd0105/librepods can stream AAC-ELD on Pixel Phones with Tensor CPU.

Best,

[kavishdevar]

Does this enable two-way audio streaming? I was recently looking at how iOS/iPadOS can use the AirPods mic without switching profiles. All I know is that the stream from AirPods takes place over AACP (opcode 0x17).

[wasdwasd0105]

I am not sure. You can try hooking MacOS with PacketLogger. I only know the airpods can also stream AAC-ELD with 24000hz mono in 2-way audio

[kavishdevar]

hooking MacOS with PacketLogger.

That's the problem- macOS doesn't use this high quality two-way audio. It uses mSBC. So, I can't hook with frida to see how it's parsed.

[wasdwasd0105]

MacOS uses it

[kavishdevar]

this is when activating microphone?

[wasdwasd0105]

Yes, and it is 128=AAC-ELD-Stereo-24K in hfp mode. And it is Stereo(although the sound quality is low)!
This is the codec the for the "game" mode

[wasdwasd0105]

From Claude
Apple unifies the codec-ID space across A2DP and HFP. The "mode" numbers from your prior doc (129 = AAC-ELD-Stereo48K, 130 = AAC-ELD-Stereo48K-10ms) are the literal +BCS values used in HFP negotiation. Full ladder Apple advertises:

AT+BAC=1,2,127,128,255,256
1=CVSD 2=mSBC 127=AAC-ELD-Mono-24K 128=AAC-ELD-Stereo-24K
129=AAC-ELD-Stereo-48K-512s 130=AAC-ELD-Stereo-48K-480s (10ms)
255=SWB-Mono 256=LC3