Hacking on PulseAudio

hacking-pulse.md

Let's take the example of needing to build webrtc-audio-processing with some changes, and then PA against that

Building webrtc-audio-processing

This follows standard the autotools procedure for a prefixed installation:

• Checkout the code, cd in
• ./autogen.sh --prefix=${HOME}/prefix/webrtc-audio-processing
• make && make install

There is now a standard install in ~/prefix/webrtc-audio-processing and we can use pkg-config to pick up that path for headers and libs using $PKG_CONFIG_PATH in the environment. This trick works with any library that provides pkg-config files.

Building pulseaudio

If you don't already have it, you might want the required dependencies from your distro using sudo apt-get build-dep pulseaudio on Debian or sudo dnf builddep pulseaudio on Fedora.

We'll also run the build in a separate directory this time, so it's easy to wipe it out and create a fresh build without having to muck around with the checked out code.

• Checkout the code, cd in
• `NOCONFIGURE=1 ./bootstrap.sh
• mkdir build && cd build
• ../configure --prefix=$HOME/prefix/pulseaudio --localstatedir=/var --with-udev-rules-dir='${prefix}/lib/udev/rules.d' --with-systemduserunitdir='${prefix}/lib/systemd/user' --sysconfdir=/etc PKG_CONFIG_PATH=$HOME/local/webrtc-audio-processing/lib/pkgconfig
• make
• ./src/pulseaudio -vvv

That's it!

• The --localstatedir=/var makes it so existing applications will continue to look in /var/... for the PA socket
• The udev and systemd rules dir overrides make sure we don't write to system directories
• Using --sysconfdir=/etc allows us to just pick up the system config without doing a make install. If you plan to do a prefixed install, skip this flag so you don't overwrite system config.

Misc. tips

• pactl info tells you a bunch of things about the running instance
• PULSE_SERVER in the environment lets you configure what PA instance your app should talk to
  • Pro-tip: this can also be a PA instance on the network with module-native-protocol-tcp loaded (you might want to set auth-anonymous=true in modargs if you don't want to worry about pesky security concerns)
  • Pro-tip 2: this means you can also run pavucontrol on your desktop against PA on your device
• pactl list sinks short (also works for other objects) gives you a quick way to look up devices without getting lost in the full pactl list output