< Development‎ | Tutorials‎ | Debugging
Revision as of 02:41, 18 June 2012 by Apachelogger (Talk | contribs) (add backend_debug used in pgst 4.6 and pvlc 0.6)

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Environment Variables

In general, there is one easy way to give Phonon devs all the information they need to help fix your problem.

Set these environment variables:

$ export PHONON_DEBUG=5

Then run your program. The terminal will fill up with gobs of debugging output.

Phonon-GStreamer debugging

Drawing a dot diagram

$ export GST_DEBUG_DUMP_DOT_DIR=/tmp
$ # run your program
$ dot -Tpng -oimage.png < /tmp/

Even more verbose output

Phonon-gst has some fancier debug options available. In addition to PHONON_GST_DEBUG, there is PHONON_GST_GST_DEBUG. Setting it to 8 or so will cause the gstreamer libraries to produce copious quantities of debug output. We're talking thousands of lines of what seems to be useless noise. Roughly 1% of it is useful, but the phonon-gst devs can easily decipher it and drill down to the important bits.


Pulseaudio and phonon try their hardest to get along. Sometimes, it doesn't work. Luckily, there is a way to test gstreamer and pulseaudio to see who is at fault.

$ gst-launch filesrc location=/usr/share/sounds/KDE-Sys-Log-In.ogg ! decodebin2 ! audioresample ! audioconvert ! pulsesink
$ gst-launch filesrc location=/usr/share/sounds/KDE-Sys-Log-In.ogg ! decodebin2 ! audioresample ! audioconvert ! alsasink

If they both work flawlessly, blame Phonon-GStreamer.

If the first works but the second doesn't, you might have an exotic sound setup that involves tweaking the alsasink parameters to reflect what pulseaudio does to alsa.

If the second works but the first doesn't, you can blame pulseaudio.

Another way to confirm this is by setting the PHONON_GST_AUDIOSINK environment variable. Setting it to e.g. "pulsesink" uses the pulseaudio sink.

Recreating the phonon-gst pipeline

Phonon-GStreamer creates predicable pipelines. In general, they look like this:

filesrc -> decodebin2 -> queue -> audioresample -> audioconvert -> pulsesink
                    -> ffmpegcolorspace -> queue -> xvimagesink

If the input stream isn't coming from a file, it is likely coming in via KIO which pipes it into an abstractmediastream. If pulseaudio isn't used, then replace pulsesink with something of alsasink, osssink, or somesuch.

Recreating the playback stream of some video file can be done as such:

$ gst-launch filesrc location=/path/to/video ! decdebin2 name=dec ! audioresample ! audioconvert ! pulsesink \
    dec. ! ffmpegcolorspace ! xvimagesink

DVD playback is a bit different:

  (subpicture stream)
rsndvdbin -> dvdspu -> ffmpegcolorspace -> queue -> xvimagesink
      \-> queue -> audioresample -> audioconvert -> pulsesink

This is built with the following:

$ gst-launch rsndvdbin ! dvdspu ! ffmpegcolorspace ! queue ! xvimagesink \
    rsndvdbin0 ! dvdspu0.subpicture \
    rsndvdbin0 ! queue ! audioresample ! audioconvert ! pulsesink

Building Phonon from source

If you want to have a newer Phonon build than 4.4.3 which is currently shipped by most distributions in KDE 4.6, you can build from source (git). Phonon is now located on

Get Dependencies

Deb-based distros, run
sudo apt-get build-dep phonon
to be sure you have all dependencies installed.


sudo zypper si -d phonon

Install git

In Kubuntu, Debian, etc.:
sudo apt-get install git-core
In Archlinux:
sudo pacman -Sy git
In Gentoo:
sudo emerge -av dev-util/git
In OpenSuSE:
sudo zypper install git

Install ccache to speed up compilation

Install the package from your distribution and set the size of the cache to 2 GB with the command
ccache -M 2G

This will take 2Gb of space in your local directory. Enable the use of ccache by adding it to your local .bashrc, described below.

Define the PATH and local environment

Append the following to $HOME/.bashrc:

export PATH=$HOME/kde/bin:$PATH
export PATH=/usr/lib/ccache:$PATH

Reload your edited .bashrc:

source $HOME/.bashrc

NOTE: if you are not using the bash shell, edit your proper shell config file (~/.zshrc or ~/.tcshrc or whatever it may be).

Make KDE aware of Phonon’s location

echo 'export KDEDIR=$HOME/kde' >> $HOME/.kde/env/
echo 'export KDEDIRS=$KDEDIR' >> $HOME/.kde/env/

Some distributions call the above folder $HOME/.kde4/, such as OpenSuSE.

Install locally

Install in your $HOME dir):

mkdir $HOME/kde && cd kde && mkdir src && cd src
git clone git://
cd phonon && mkdir build && cd build
cmake -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_BUILD_TYPE=debugfull $HOME/kde/src/phonon
sudo make install

To update your build, it's even easier:

cd ~/kde/src/phonon
git pull
cd build && sudo make install

Build locally from a tarball

This is 4.4.4 for example:

cd ~/kde/src/
tar xf phonon-4.4.4.tar.bz2
cd phonon-4.4.4 && mkdir build && cd build 
cmake -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_BUILD_TYPE=debugfull $HOME/kde/src/phonon-4.4.4
sudo make install