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There's big file with ext2 with ARM Debian where I can chroot to.

There's functional mplayer (I can -ao pcm or -vo yuv4mpegpipe) there.

How to record/play sound (or video) from this Debian? Is there things that emulate ALSA/OSS/Whatever to use usual linux programs and android ones side by side? May be there's pulseaudio server for android?

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2 Answers 2

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I managed to make it sound by writing to /dev/msm_pcm_out:

mplayer something.mp3 -ao pcm:file=/dev/msm_pcm_out

Sound is choppy and it looks hacky in general.

Video output is something like -vo fbdev:/dev/graphics/fb0.

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Not all Androids may have a PCM output device in /dev, as Vi0's answer requires.

A more general solution is to setup Pulse to stream system audio to a TCP port on your device. Then you can use Simple Protocol Player or PulseDroid in your Android environment to play the stream.

To eliminate chop/lag in VLC, MPlayer, and Audacity, it was necessary for me to choose ALSA as the output device and Pulse as the mixer (in these programs' options).

Steps I used on my Amazon Fire 7" 2015 / CM12 / Debian Wheezy chroot:

  1. Install pulseaudio in the chroot: sudo apt-get install pulseaudio.
  2. As suggested by a comment on meefik's github, I removed the line load-module module-console-kit from the file /etc/pulse/default.pa.
  3. Run pactl list | grep 'Name\|Description' and identify a module that monitors system audio. I successfully used 'Dummy Output Monitor' named auto_null.monitor.
  4. Write a corresponding shell script pashare as follows (credit to AlexAndersan on SuperUser):
#!/bin/sh
case "$1" in
    start)
        $0 stop
        pulseaudio --start
        pactl load-module module-simple-protocol-tcp rate=44100 format=s16le channels=2 source=auto_null.monitor record=true port=8000
        ;;
    stop)
        killall pulseaudio
        pactl unload-module `pactl list | grep tcp -B1 | grep M | sed 's/[^0-9]//g'`
        ;;
    *)
        echo "Usage: $0 start|stop" >&2
        ;;
esac

Make sure the rate and port arguments match your settings in Simple Protocol Player (on the Android side). PulseDroid demands rate=48000, which means higher throughput, and could possibly introduce chop/lag.

I added the pulseaudio --start and killall lines because pulse would not start automatically in my chroot.

  1. Make the script executable and run it:
chmod 755 pashare
sudo mv pashare /usr/local/bin/
pashare start

  1. Configure your chroot media players to output to ALSA, with Pulse mixer. I had to set this manually, to eliminate choppy audio:

    • VLC: In Tools->Preferences->Audio, set Output module: ALSA audio output, and Device: Playback/recording through the PulseAudio sound server.

    • GNOME MPlayer: In Edit->Preferences->Player, set Audio Output: ALSA.

  2. In Android, start Simple Protocol Player or PulseDroid on IP address 127.0.0.1 (loopback) and set the other option(s) to match your pashare script.

Note that Android treats the app like a music player, and will kill it if another app tries to play music, or if it decides to free up the CPU. There are probably workarounds for this.

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  • Is it only about playing or also about recording?
    – Vi0
    Jul 26, 2016 at 10:34
  • @Vi0, this also worked for [limited] recording within the chroot... just select ALSA in Audacity's input pop-up. It'll record whatever's playing through alsa.
    – user140691
    Jul 26, 2016 at 11:46
  • I had trouble with e.g. Freeciv using this answer, because it uses SDL for audio which seems to auto-select the pulse driver (not alsa), and there's no way to configure that w/o recompiling.....
    – user140691
    Jul 26, 2016 at 11:50

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