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GSoC 2009 (Read)

Due to a lack of time our core developers will be able to dedicate to Mixxx this Summer, Mixxx will not be participating in GSoC 2009. This page contains documentation from GSoC 2008.


This page collects some introductory information which we hope will be of use to our students, especially during the community bonding phase of GSoC 2008.


As you all already know, Mixxx is a cross-platform DJing application which recreates in software many of the features of a traditional hardware DJing setup.


Mixxx was originally written by Tue Haste Andersen and Ken Haste Andersen in 2002 partly as a research project into user interface design for Tue's PhD. The project continued to develop until some time around 2004 when Tue moved on to full-time employment and no longer had time to manage the project. Although development continued, there were no new releases and Mixxx drifted somewhat in this period until early 2006 when Adam Davison became the lead developer and released Mixxx 1.5.0. For the last 2 years, the project has been steadily growing leading up to our inclusion in Summer of Code for the first time last year.

Technical Info

Mixxx was designed with a strong focus on cross-platform portability. Qt gives us a very strong cross-platform graphics toolkit and has additional benefits like a thorough set of portable data structure implementations (eg. QMap, QList, etc.). Mixxx was originally written using Qt 3, but during the summer of 2007, Mixxx was ported to Qt 4. At the same time, we moved away from a custom qmake-based build system, instead opting for SCONS. SCONS is a python-based build system that has easy syntax, and is still very powerful. Our single SConscript file (in the “src” directory) checks all of our dependencies and builds Mixxx on Windows, OS X, and Linux.

New experimental (and potentially unstable) features are coded such that they are only enabled when they are turned on at compile-time. For example, during its development, recording was turned on by compiling with scons recording=1. Now that recording is stable and reasonably well tested, the compile flag has disappeared and it is always built into Mixxx. For a full list of build flags, run scons —-help

One of our goals is to minimize the amount of platform-specific code we have. Before we moved our audio core to PortAudio, we had separate backend for ALSA, CoreAudio, ASIO, WMME, etc. This is a losing strategy for several reasons:

  1. Our code base was inflated by a factor of X.
  2. If we wanted to add new features (eg. multiple soundcard support), it was going to require modifying 5 different audio backends. Furthermore, nobody has the time/energy/computers to test Windows, OS X, and Linux implementations of stuff.

By switching to PortAudio, the platform-specific audio code moves to an external library, our audio core is now much more flexible and any improvements we make to PortAudio will be of benefit to the whole open source community. Currently, our MIDI code still has three different backends (Windows, CoreMidi, and ALSA-seq), although creating a single PortMidi-based backend is something we will consider in the future.


As with any project, there are some names which you will see. Here's a list of some:

Mentor Team in Alphabetical Order

  • Garth Dahlstrom - Long-time Mixxx contributor (since Mixxx 1.4.something). Most active on Hercules device support on Linux (libDJConsole)/Windows(MIDI), various interface tweaks, and occasional build script tweaks. Has a Hercules Mk2 and a Hercules RMX console, both do MIDI on Windows.
  • Adam Davison - Lead developer and organisation admin for GSoC. Knows about Windows development, MIDI control, skins and probably some other stuff he can't remember now.
  • Albert Santoni - Has written loads of code for Mixxx. Knows about Mac/Linux development, wrote the scons build system, vinyl control and more.

Albert and Garth are based in Canada (EST -5), while Adam can be found in either London or Geneva (GMT +0 or CET +1 respectively).

On IRC, Garth is jumpkick, Albert is asantoni, Adam is adam_d.

Other Notables in No Good Order

  • Tue and Ken Haste Andersen - As mentioned above, the original authors of Mixxx, no longer with the project.
  • Adam Bellinson/DJ Thread - Long time Mixxx user, does a weekly live show with Mixxx over on
  • John Sully - Contributor since Spring 2007, wrote recording, new EQ code, improved VU meters, and more.
  • Paweł Bartkiewicz - SoC student from last year, implemented LADSPA support in Mixxx
  • Micah Lee - SoC student from last year, worked on BPM detection in Mixxx
  • Nathan Prado - The final 2007 SoC student, worked on the library interface
  • Mark Hills/radiomark - Author of xwax, an open source vinyl control project which Mixxx relies on

Managing Expectations

When you enter the work world, you'll hear managers drone-on about how with better communication all the bad things that happened could have been avoided.

Its only partially true… Problems are almost assured to crop up from time to time. To be really successful in handling them, you must also include how you deal with the people you report to and the clients you provide service to in your approach to solving them. [In this case mentors and the community of Mixxx users]. This is called managing expectations.

Some Advice for Students

  • Take the initiative. Don't sit around waiting for someone to ask you if you need help. If you are stuck, make an effort to understand the problem so you can ask good questions, then ask… ask the Google, ask the wiki, ask on IRC, ask a mentor, ask the mixxx-devel mailing list.
  • We expect you to encounter problems, all of the mentors are here to help all the students, so please bug us.
  • Try to set realistic goals and timelines for yourself. This comes with experince, knowing the code base and the problem domain. (Mentors should try to help with this.)
  • Over-communicate rather then under-communicate.
  • Help each other out. We are all on the same team. Everyone will pass/fail on their own, but we want everyone to pass big time (we hope to get some amazing contributions from all of you).
  • Feel free to dabble in other parts of Mixxx that interest you. Don't feel confined to just your project scope. Remember though, that you will be evaluated on your project's progress.

You've been selected because you presented great proposals, you've got the skills to pull them off and because we sense in each of you a passion for Music/DJing.

What Mentors Should Be Doing For You

You all have an assigned mentor, he has the following responsibilities:

  • Having contact with you at least once a week (during the coding phase at least) to get a progress update - any problems, what happened last week, what's planned for the week coming up
  • Evaluating your progress for Google
  • Getting to know you and being your first point of contact for any more personal issues you may encounter

In the highly unlikely event that you have a problem with your assigned mentor, you should attempt to discuss it with them. Should this fail, Adam Davison is the organisation administrator and will deal with any such matters in confidence. If Adam is your mentor, you're screwed… just kidding :) you can speak to any other member of the mentoring team if you feel more comfortable.

In addition to this, you will be getting support from all 3 mentors. Each member of the mentoring team has different expertise, different insights and not least of all different timezones. The whole team will do the following:

  • Help students find solutions to problems, brainstorming, offer suggestions: approaches, better coding style, optimizations, etc…
  • Offer feedback on patches
  • ???
  • Profit!

Up to a point, the more people that you discuss a technical issue with, the better. The recommended ways for having technical discussions are in #mixxx on IRC or on mixxx-devel

Some First Activities

You're probably wondering what exactly you can do in the community bonding phase. Here is a list of things:

  • The absolutely first thing you should do, as soon as possible, is sign up to the mixxx-devel mailing list and briefly introduce yourself to the broader community; who you are, where you are based out of, what your IRC nick is and what you are working on for GSoC…
  • You will also want to find an opportunity to have a chat either on IRC or by e-mail, with your mentor, especially to let him know your commitments and schedule over the next couple of months.
  • Have a browse through at least some, if not all, of the sources of information listed in the Community Resources section below.
  • Sign up to to become a wiki editor
  • Discuss your plans and designs with the community, people may well be able to suggest things you haven't thought of, or offer possible refinements
  • Check out the code base from SVN
  • Try building Mixxx - if you are building on a Debian/Ubuntu flavour of Linux check out these Wiki pages, if you are on Windows check here, or on OSX check here
  • Check out the developer tools page

We understand that many of you will have varying levels of school commitments over the next few weeks but you should try to do as many of these things as possible, this will leave you in an excellent position to start work as soon as the coding phases begin.

Community Resources

There are a bunch of places where you can interact with the Mixxx community, here's a list of the main ones:

  • mixxx-devel - This mailing list is the centre of all development related discussion. You should all subscribe here:, right away if you haven't already.
  • IRC - More immediate than mixxx-devel if the right person is available, #mixxx on freenode although I think you've all been there already
  • Wiki - A small but growing collection of useful documentation. You should definitely add to it if you learn things that aren't already written here.
  • Forum - We now have a brand new forum which will hopefully grow and bring the user community closer to the development team over the next few months, have a browse here:
  • Blog - Irregular articles about Mixxx development progress:
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soc_student_info.txt · Last modified: 2009/03/09 14:46 by gamegod