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Audio runtime

uDroid provides Linux playback and optional microphone input through an app-owned PulseAudio server. PulseAudio talks to Android through its OpenSL ES sink and source modules; PRoot clients talk to PulseAudio over authenticated device-local loopback.

flowchart LR
    A["Linux application in PRoot"] -->|"PulseAudio native protocol on loopback"| B["uDroid PulseAudio"]
    B -->|"OpenSL ES output"| C["Android speaker or selected output"]
    D["Android microphone"] -->|"OpenSL ES input - opt in"| B
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The listener is bound only to 127.0.0.1; it never uses Wi-Fi, mobile data, or an external network interface. PRoot does not reliably translate pathname-based Unix socket connect() calls, so uDroid uses PulseAudio's loopback transport and bind-mounts only its private authentication cookie into supervised guests. Terminal, desktop, and graphical application launches receive:

PULSE_SERVER=tcp:127.0.0.1:4713
PULSE_COOKIE=/tmp/.udroid-pulse/cookie

Using it

Open an installed Linux system in uDroid and use its Audio controls. Speaker playback is enabled by default. Microphone input is off by default and requires Android's microphone permission. Android shows its microphone privacy indicator while capture is active.

Linux applications need a PulseAudio-compatible client library. Many desktop images already include one. If pactl or paplay is missing, install your distribution's PulseAudio client utilities; the server itself remains on the Android side and does not need to run inside the rootfs.

Useful guest checks:

printf '%s\n' "$PULSE_SERVER"
pactl info
pactl list short sinks
pactl list short sources

Lifecycle

  • Settings are stored per installed rootfs.
  • Changing a setting updates a running rootfs without restarting its desktop.
  • The audio server stops with the supervised Linux runtime.
  • Android service recreation restores playback, but deliberately leaves the microphone off until the user returns to uDroid and starts or enables it again.
  • Resetting or deleting a rootfs clears its saved audio settings.

Packaged runtime

tools/build-pulseaudio-assets.sh reproduces the ABI-specific runtime archives from checksum-pinned official Termux packages listed in tools/pulseaudio-packages.tsv. Only PulseAudio, the native TCP protocol, the OpenSL ES sink/source, and their ELF dependency closure are packaged.

This bridge is independent of fake-media-accel. Audio PCM transport and video codec acceleration have different lifecycles and data paths.