GSOC 2025 Ideas

Student Project Ideas for Google Summer of Code 2025

This page lists the suggested tasks to build a 90 hour (small sized) a 175 hour (medium sized) or 350 hour (large) project for Google Summer of Code 2025. The ideas are already assigned to example projects, but you are encouraged to use them for building your own project adding your own ideas and make it suit perfectly to you, your skills and your time line.

If you are interested in applying to GSoC, read GSoC Advice before applying or getting involved. Only beginner contributors that are active members of the Mixxx community are accepted. If this is not the case yet, just say hello at https://mixxx.zulipchat.com and discuss your Ideas and discus cases with us.

Adding an AI infrastructure with cross-platform hardware acceleration

Typical AI applications in the DJ environment (STEM separation, music analysis) require very high computing power. However, as the commercial DJ software DJay Pro demonstrates, it is possible to perform these on modern laptop hardware in real time with high audio quality. This is made possible by the use of the dedicated Neural Processing Unit (NPU) or powerful Graphical Processing Units (GPU). As cross-platform software, Mixxx must be able to do this on:

• macOS (ARM M1/2 with Neural Engine NPU)
• macOS (x64 with GPU only)
• Linux with various NPU and GPU solutions from different manufacturers
• Windows with various NPU and GPU solutions from different manufacturers

Today, there is only one AI framework that supports full hardware acceleration across all these platforms, which is ONNX Runtime (onnxruntime.ai). This project is about the integration of ONNX Runtime with ExecutionProviders for CPU (all operating systems), as well as at least one NPU or GPU acceleration solution into Mixxx. This project explicitly includes contributions to third-party projects, in particular to the package managers VCPKG and the Linux distribution Debian/Ubuntu, which Mixxx uses to integrate dependencies. A further aspect to handle is, that these libraries, as well as, the AI models itself are significiantly larger than the current dependencies that come with Mixxx. This requires the development of suitable solutions for the continuous code integration (CI) and for the distribution to the end users.

• Expected Outcome: ONNX Runtime with ExecutionProviders for CPU (all operating systems), as well as at least one NPU or GPU acceleration solution builds within the Mixxx environment. All changes on third-party code is contributed upstream to the particuar projects.
• Skills: Knowledge of CMake, C++. Basic experience with contributing packages to package managers/Linux distributions.
• Possible Mentor: Jörg
• Difficulty: Medium
• Size: 350 h

Converting Demucs v4 (Hybrid Transformer) AI model to ONNX format

With Demucs v4 https://github.com/adefossez/demucs, there is a high quality stem separation model available as OpenSource. But, this is a PyTorch model that cannot be used in a C++ project with support for any kind of acceleration hardware. To allow this, the model needs to be converted to the ONNX format to run in ONNX Runtime. This conversion is not trivial, as the DSP functions required for most audio applications are not equivalent in PyTorch and ONNX. In particular, the short-time Fourier transformations STFT/ISTFT must be remodeled in ONNX to enable the automatic ONNX export of PyTorch. It must be demonstrated that the exported ONNX model produces equivalent results as the original PyTorch model. Therefore a minimal C/C++ command line program supporting MP3 files and embedding ONNX Runtime and the exported model should be created.

• Expected Outcome: The model runs in ONNX Runtime and generates similar results as the original
• Skills: Basic knowledge of C/C++. Sound experience with the creation of AI models - preferably in ONNX.
• Possible Mentor: Jörg
• Difficulty: Difficult
• Size: 175 h

AI driven STEMS seperator

Currently creation of stem files files is a manual process in preparation of a DJ set. Many DJs can't effort the time and the storage space for extracting stem files. In this project a temporary stem file shall be created on demand from the Mixxx GUI. Part of the project shall be evaluation of already published algorithms. Integration of one of them into the Mixxx analyzer and handling of the caching an the required GUI for this feature.

• Expected Outcome: Playing and remixing of stem files
• Skills: Good understanding of sound processing, C++
• Possible Mentor: Niko
• Difficulty: Medium
• Size: 175 h

Using The Harmonix Set to automatically evalute the output of our music analyzers

The Harmonix Set https://github.com/urinieto/harmonixset repository contains human annotated labels for 912 Western Pop music tracks. This is a great base to benchmark current and future music analyzers in Mixxx. This project is about the automatic execution of the Mixxx Analyzer in a local development environment using all tracks of the Harmonix Set, that are available on the developer's local hard disk and generate a report that visualizes the deviations.

• Expected Outcome: A lightweight tool or script that can be executed out-of-the-box on Windows, macOS and Linux.
• Skills: Experience C++ and a common scripting environment like Python
• Music files: The Mixxx project cannot provide the music files, so the students must have a larger number of the music files listed in The Harmonix Set available themselves.
• Possible Mentor: Jörg
• Difficulty: Easy
• Size: 175 h

Turn table inertia model

Some Controller mappings have implemented a Spin-Up/Spin-Down to mimic the inertia of a turn table. This should be generalized into a "turn table inertia model" that models all moving parts like the platter and the slip pad.

Some DJ actions on the controller or keyboard should be applied to that model rather than directly to Mixxx transport unit. The transport is than controlled by the turn table model. This should make all transport effects/actions sound more natural.

It allows Spin-Up/Spin-Down effects and keyboard/mouse scratching.

Part of the project is to record the spin up of a real turn table to get to know of the real acceleration curve and model this via software.

These are related feature requests: https://github.com/mixxxdj/mixxx/issues/8867 https://github.com/mixxxdj/mixxx/issues/11250

Here you can see such a model in action:

• Expected Outcome: A flawlessly working spin up and down effect accessible without controller
• Skills: Good understanding of sound processing, C++
• Possible Mentor: Daniel Schürmann
• Difficulty: Medium
• Size: 350 h

Scratch smoothing

Our scratching algorithm suffers from jitter noise created by the latency of the midi messages. It also suffers from a so called sticker drift, an incrementing offset shifting away form the original scratch sample. Part of this project is to filter the discrete messages from the controller in a way that you can either "play" the track without much wobbling by turning the jog wheel, and keep the position during scratching.

We may also make use of the time stamps of the midi messages. https://github.com/mixxxdj/mixxx/issues/6951

The required controller can be provided as a loan.

• Expected Outcome: Wobble fee scratching using a joggwheel
• Skills: Good understanding of real time processing, C++
• Possible Mentor: Daniel Schürmann
• Difficulty: Hard
• Size: 350 h

Sharp Scratching

Currently crossfader changes are stretched on audio buffer time to avoid pop sounds. This is too long for some scratching styles. During this project you need to dive into the audio engine code find the code that is responsible for crossfading and make it independent from the audio buffer size.

https://github.com/mixxxdj/mixxx/issues/8899 https://github.com/mixxxdj/mixxx/issues/11253

• Expected Outcome: Cut type crossfader curve, suitable for scratching.
• Skills: Good understanding of sound processing, C++
• Possible Mentor: Daniel Schürmann
• Difficulty: Medium
• Size: 175 h

Resample options

Mixxx uses a linear resample when scratching. This is blazing fast, but the sound can be improved. Here Mixxx should provide more resample options. This project involves to review the already used resample libraries RubberBand and Soundtouch and compare them with other candidates. The one with the best Sound/CPU load trade of shall be selected. Make sure that it supports on the fly changing of the sample rate without artefacts. This project may also involve to contribute a missing feature to such library.

https://github.com/mixxxdj/mixxx/issues/9328

• Expected Outcome: Optional replacement of the linear resampler.
• Skills: Good understanding of sound processing, C++
• Possible Mentor: Daniel Schürmann
• Difficulty: Easy
• Size: 175 h

Graceful recovery of controllers

If a controller is accidentally unplugged it has to be manually reconfigured, which is a party stopper. Mixxx shall do it automatically. This project has two stages, fist behave like a real DJ: fix the issue but faster. So the the time of silence on the dance floor is kept short.

The advance stage of this project is to implement real Hot Plug And Play. Here you shall evaluate alternative midi libraries like libremidi. You likely need to touch the low level inside these third party libraries and counterpart inside Mixxx.

The required controller can be provided on loan.

• Expected Outcome: Re-power the controller and continue to use it, on your target platform.
• Skills: Good understanding of the USB stack, C++
• Possible Mentor: Jörg Wartenberg
• Difficulty: Easy / (Hot Plug And Play = Difficult)
• Size: 90 h / (Hot Plug And Play = 350 h)

First class Pipewire support

Currently Mixxx supports Pipewire via Portaudio and Jack. These two glue layers leads to a limited feature support with a weak user experience. In this project you need to consider solutions to improve the situation. Desired features are

• Better audio routing using external tools

• Route sound to/from other applications from inside Mixxx

• Access to DAC timing info of the soundcards

• Acesss to analog volume settings of the soundcards.

• Expected Outcome: A rock solid interface to Pipewire.

• Skills: Experience with Audio processing and C++

• Possible Mentor: Daniel Schürmann

• Difficulty: Difficult

• Size: 350 h

Track encoding offset correction

Different codecs used to encode sound files introduce slight shift in the audio samples comparing the input with the output stream. This is no issue when you use always the same file and the same decoder. It becomes however an issue when the decoder is updated or replaced because than all stored metadata like waveform, beat-grids and cue points are no longer at the correct position. To protect against surprises Mixxx has unit-tests to verify that seeks inside that track do not introduce an offset and checks if the fist sound sample can be found at the expected time.

We have currently the issue that the Microsoft has introduced such a breaking change in Windows 11. https://github.com/mixxxdj/mixxx/issues/11094 In this project we need to investigate the issue and implement a fix so that the stored metadata of a user are still valid after an upgrade to Windows 11. As a project extension, this may also fix an issues that prevents us from moving to ffmpeg as an encoder wrapper where the underlying encoder library is no longer in control of us.

• Expected Outcome: No Beat-Grid offset after Windows 11 update
• Skills: Experience and C++
• Possible Mentor: Daniel Schürmann
• Difficulty: Medium
• Size: 175 h (350 h for a general solution)

Address sanitizer facilities

Sometimes we have reports of hard to find crashes that my have to do with dangling pointer or other memory addressing issues. When hunting such a general environment that helps to find it would be great. However it is often not worth the effort for that particular issue and that's why we don't have it. This project is for contributors who have real experience with such memory sanitizer facility. We like to learn from you, what is reasonable to use and how we can integrate checks in out continuous integration. This may also something integrated in Mixxx itself to have more info users can provide in case of a crash.

• Expected Outcome: A new workflow how to deal with crasher bugs along with an improved set of tools.
• Skills: Experience with address sanitizer tools like ASAN or Valgrind and CMake
• Possible Mentor: Jörg Wartenberg
• Difficulty: Medium
• Size: 175 h

Something Else!

As always with Summer of Code, you aren't limited to the suggestions we've made here. If you've got a great idea for a project involving Mixxx then we're looking forward to hearing about it. We recommend spending more than a few days using Mixxx and participating in the community to develop a better understanding of areas where Mixxx could use improvement. Our issue tracker is full of feature requests and other ideas scattered throughout, so if you browse through it, you may find many more ideas for GSoC projects.

IMPORTANT: You should contact us first to get feedback if you're going to submit a proposal for your own project idea! We very rarely approve ideas students propose. If you're not already experienced with DJ equipment, we recommend sticking with one of the ideas above.