audio - How to Play Sound from Termux when using Linux?

I have a problem with audio streaming that I can not listen audio from Pulseaudio when using VNC with a Linux Desktop Environment.

However it works if I export the audio to XSDL. But the problem is that after I exit the application the sound does not work in the background.

I know that Pulseaudio only supports Xorg servers, so how to stream audio to VNC or any other application on Android and to run it in the background.

I know that there is an application Simple Protocol Player that listens to pulseaudio sound from Xorg Server, but it does not work for me and I do not know the reason.

Answer

There are two possibilities I know of, to play sound from a Linux environment on Android device:

• Play through native ALSA libraries


• Stream through PulseAudio
  
  
  
  • Forward to X Server (on UNIX or TCP socket)
  
  
  • Stream over IP (TCP or UDP) e.g. when using VNC
  
  
  
  

Second and third options work through PulseAudio libraries i.e. different modules and protocols (pulseaudio package should be installed on Linux distro) while the first works natively through ALSA kernel module/drivers.

But ALSA drivers loaded by Android can't be controlled (at least I could not) through standard Linux userspace tools in straightforward manner because they aren't compatible (refer to changes in Linux kernel by Google, and the closed source proprietary blobs providing hardware support). However Android kernel lists devices in /dev/snd/ which can be manipulated to direct ALSA towards Android sound card. Access to /proc/asound/ is also required which isn't possible without root. See details in this answer and complete tutorial can be found here. It works, but not for all sound formats. ALSA project is here.

Also there are more customized solutions that work with ALSA and PulseAudio both such as Music Player Daemon.

X Server:
XSDL Server is the only well developed X server Android app I know of, no more developed unfortunately. It has a built-in PulseAudio server with module-cli-protocol-tcp already loaded, listening on standard port 4712 by default. Once the X Session is started on Linux, we can direct sound from Linux PulseAudio client libraries to XDSL PulseAudio server by setting the following environment variable on Linux:

$ export PULSE_SERVER=tcp:127.0.0.1:4712

^{* 127.0.0.1 indicates that Linux and XDSL are running on same device}

Or to set permanently, edit file:

# /etc/pulse/client.conf or ~/.config/pulse/client.conf


default-server = tcp:127.0.0.1:4712

Now any media player running in this environment that makes use of PulseAudio client libraries, will stream its audio to XDSL app. You can forward X session display and sound to X server running on a PC as well but that needs a more complicated setup.

VNC:
VNC protocol by default doesn't support sound. However, PulseAudio server can stream over TCP/UDP using different protocols. There are apps available for Android that can play simple protocol (e.g. Simple Protocol Player) and real-time transport protocol (e.g. VLC). For this we need to load the related PulseAudio module.
To setup local PulseAudio daemon, first of all comment out following lines:

# /etc/pulse/default.pa

#ifexists module-console-kit.so
#load-module module-console-kit

#.endif

Otherwise daemon will fail to start if /usr/lib/pulse*/modules/module-console-kit.so exists but consolekit package isn't installed (which is deprecated, replaced by systemd-login and no more present on many Linux repos).

Ensure that autospawn is set to yes so that we don't need to start daemon manually and it is auto started by Desktop Environment. Not necessary if we start daemon manually.

# /etc/pulse/client.conf

# Autospawn a PulseAudio server/daemon when needed
autospawn = yes

Now start pulseaudio daemon and note the value of source, for me it's auto_null.monitor:

$ pulseaudio --start && pactl list | grep -A2 -i RUNNING
$ DISPLAY=:0 pulseaudio --start

Load simple-protocol module:

$ DISPLAY=:0 pactl load-module module-simple-protocol-tcp rate=48000 format=s16le channels=2 source=auto_null.monitor record=true port=8000 listen=127.0.0.1

Or to set permanently, edit file:

$ echo 'load-module module-simple-protocol-tcp rate=48000 format=s16le channels=2 source=auto_null.monitor record=true port=8000 listen=127.0.0.1' >> /etc/pulse/default.pa

Following should be enabled in DE startup settings, necessary because some programs such as emixer on Enlightenment Desktop Environment works only if PulseAudio server in local X server is published:

$ DISPLAY=:0 start-pulseaudio-x11

Start Simple Player app and match bitrate and port set in above command i.e. 48000 and 8000 in my case. Don't use listen=127.0.0.1 if you want to listen on PC too.

I have tested both of PulseAudio based solutions on ArchLinuxARM and Ubuntu, and they work without root access. However SELinux may restrict access to certain resources if running in non-root context. Also, in order to get network access and create sockets, you have to be member of inet (3003) group necessarily. All apps with android.permission.INTERNET granted are member of this group.

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