sndcpy

This tool forwards audio from an Android 10 device to the computer. It does not require any root access. It works on GNU/Linux, Windows and macOS.

The purpose is to enable audio forwarding while mirroring with scrcpy. However, it can be used independently.

Requirements

• The Android device requires at least Android 10.
• VLC must be installed on the computer.

Get the app

Download the latest release:

• sndcpy-v1.0.zip
  SHA256: 4495f752fc192535cd5208ace4d35d2ba644beb9aabb0e288ae339861ad6782b
• sndcpy-with-adb-windows-v1.0.zip
  SHA256: 42b89b7b557b9fdf0c6f3802eac171a0e5610a50a1d615a290ed7f41cba7053d

On Windows, for simplicity, take the second archive, which also contains adb.

Alternatively, you could build the app.

Run the app

Plug an Android 10 device with USB debugging enabled, and execute:

./sndcpy

If several devices are connected (listed by adb devices):

./sndcpy <serial>  # replace <serial> by the device serial

(omit ./ on Windows)

It will install the app on the device, and request permission to start audio capture:

Once you clicked on START NOW, press Enter in the console to start playing on the computer. Press Ctrl+c in the terminal to stop (except on Windows, just disconnect the device or stop capture from the device notifications).

VLC may print this error message once:

main stream error: connection error: Connection refused

It is "expected", just ignore it.

The sound continues to be played on the device. The volume can be adjusted independently on the device and on the computer.

Uninstall

To uninstall the app from the device:

adb uninstall com.rom1v.sndcpy

Apps restrictions

sndcpy may only forward audio from apps which do not prevent audio capture. The rules are detailed in §capture policy:

• By default, apps that target versions up to and including to Android 9.0 do not permit playback capture. To enable it, include android:allowAudioPlaybackCapture="true" in the app's manifest.xml file.
• By default, apps that target Android 10 (API level 29) or higher allow their audio to be captured. To disable playback capture, include android:allowAudioPlaybackCapture="false" in the app's manifest.xml file.

So some apps might need to be updated to support audio capture.

Audio delay

This is just a proof-of-concept, so it's far from perfect.

For example, jitter may cause VLC to automatically increase its buffering, causing an unacceptable delay:

main input error: ES_OUT_SET_(GROUP_)PCR  is called too late (pts_delay increased to 377 ms)

In that case, just restart it.

Environment variables

The scripts sndcpy and sndcpy.bat use some default values which can be overridden by environment variables.

• ADB: the full path to the adb executable
• VLC: the full path to the vlc executable
• SNDCPY_APK: the full path to sndcpy.apk
• SNDCPY_PORT: the local port to forward to communicate with the device

Blog post

• Audio forwarding on Android 10