AOA audio

The purpose of this PoC is to find a solution to forward audio in scrcpy.

Build

Install the following packages (on Debian):

sudo apt install libusb-1.0-0-dev ffmpeg

Build the tool:

make

Run

Find your Android device vendor id and product id in the output of lsusb:

$ lsusb
...
Bus 003 Device 011: ID 18d1:4ee2 Google Inc. Nexus 4 (debug)
...

Here, the vendor id is 18d1 and the product id is 4ee1.

Then enable AOA audio:

./audio 18d1 4ee1 1

The last argument (1) is the audio mode (provided in the value field).

The output should look like:

$ ./audio 18d1 4ee1 1
Device 18d1:2d05 found. Opening...
Setting audio mode: 1
SUCCESS

Note that changing the audio mode changes the device product id.

Once enabled, your computer should detect a new input audio device. List the sources (provided your system uses PulseAudio):

pactl list short sources

You should see your device:

$ pactl list short sources
...
5   alsa_input.usb-LGE_Nexus_5_05f5e60a0ae518e5-01.analog-stereo     module-alsa-card.c  s16le 2ch 44100Hz   RUNNING

or:

$ ffmpeg -sources pulse
...
  alsa_input.usb-LGE_Nexus_5_05f5e60a0ae518e5-00.analog-stereo [Nexus 5 Stéréo analogique]

Play the sound with ffplay:

ffplay -vn -nodisp -f pulse -i 5

or with the full name:

ffplay -vn -nodisp -f pulse -i alsa_input.usb-LGE_Nexus_5_05f5e60a0ae518e5-01.analog-stereo

The sound of your Android device should be played on your computer.

Issues

This PoC works, but there are problems to solve before this can be implemented in scrcpy.

Find the USB device

How to find the VID and PID of the device from adb? Is there a better way than matching the serial from adb devices with the USB iSerial field?

lsusb -d 18d1:4ee2 -v | grep iSerial | grep -o '[0-9a-f]\+$'

Stop accessory

The accessory may not be stopped easily. Setting mode to 0 is not sufficient, so the device sound is redirected until the device is rebooted.

Find the audio source

Enabling audio accessory creates a new audio source on the computer, but how to find it reliably and automatically? What if the system does not use PulseAudio?

It would be great if it were possible to receive audio packets manually, so that we could play them with SDL directly.

Non-Linux system

The PoC uses libusb. What about systems like Windows?