User Tools

Site Tools


N-Deck Support

Summary and Rationale

Status: This specification is in drafting. This is a meta-specification which is dependent on the outcomes of other specifications. Please feel free to add comments.

Use Cases

  • DJ Bill is considering switching from Traktor to Mixxx. However, he makes heavy use of Traktor's 4-decks and cannot use Mixxx since it only allows 2.
  • DJ Cassandra creates crazy mashups and sometimes wants more than 2 songs to be playing at once. She needs Mixxx to support >2 decks.
  • DJ Danny wants to prepare the next 2 songs he will mix while the first 2 are playing. To do this, he needs >2 decks.
  • Engineer is building an OSS all digital radio studio and would like to use Mixx as the playout and mixing software using an external midi control board (long-throw faders, but no X-fader) but needs four deck support for station jingles etc.


This project entails a complete revamp of many parts of Mixxx.

Engine Support

The internal mixing engine must be revamped to support more than 2 decks being mixed together.

UI Support

The UI and skin file are heavily 2-deck centric. The skinning system must be either heavily modified or re-written with N-decks in mind from the start. A feature specification for this is in drafting: Skinning Engine

Preferences Dialog Considerations

Bill Good is currently working on External Mixer Mode. This will allow Mixxx users to detail where they would like outputs to be routed and mixed. Pending his design, there will be a flexible way for users to route additional sources to their preferred sinks.

Work Breakdown

This work breakdown structure (WBS) will become more detailed as the design above becomes more thorough and complete.

1. N-Deck Support
  1.1 Refactor the engine to support multiple decks / audio channels.
  1.2 Strip all 2-deck centric code out of random parts of the Mixxx codebase.
  1.3 Update preferences dialog to allow routing of each deck to an appropriate sink.
  1.4 Update/rewrite the skinning engine to allow for N-decks 
  1.5 Handle corner cases (e.g. what happens when the user wants more decks than a skin shows)
  1.6 Build a skin that has more than 2 decks in it.

Current Progress

The lp:~mixxxdevelopers/mixxx/features_hydra branch contains all the work that's been done so far.

  • The features_hydra branch has completed steps 1.1 and parts of 1.2.
  • A feature specification for 1.4 is in drafting: Skinning Engine
  • A GSOC 2010 project is addressing 1.3: External Mixer Mode

List of Places in Mixxx That are 2-Deck Centric

If you are looking for a place to contribute to this project, please tackle making a part of Mixxx on this list flexible enough to handle N-Decks.

  • Parts of mixxx.cpp
    • Now, only the “File → Load to Player” drop-downs.
  • Mixing Engine
    • EngineBuffer beat sync'ing is hard-coded to 2-decks. Working on this in features_hydra.
  • Skinning engine
    • This project is looking for project lead!
  • Library
    • The right-click context menus all only list players 1 and 2 to load a track.
    • widget/wbrowsetableview.cpp
  • MIDI Scripts
    • All MIDI scripts are only written for Player1 and Player2, but this is because most only have 2 decks worth of controls.
      • The easiest way to tackle this is to make the two live decks on a MIDI device switchable to one of the 1-N decks.
      • See the Stanton SCS.3d script for examples of how to do this…in a nutshell, replace every hard-coded call containing “[ChannelN]” with “[Channel”+Controller.Deck+“]”)
      • Need to create a “[Master],activeDecks” CO containing the number of available virtual decks for the MIDI scripts to poll
  • PlayerInfo class, which is used to share loaded-track metadata with things like Shoutcast.
    • Bruno Buccolo is working on this. He will take the potential of N-Decks into account.
  • External Mixer Mode
    • Bill Good is working on this. He will take the potential of N-Decks into account.
  • Vinyl Control is all 2-deck centric.
  • Auto-DJ is 2-deck centric
  • Preferences have some internal logic that hard-codes Channel1 and Channel2
  • MIDI Learning has some hard-coded Channel1/Channel2 stuff


If you're interested in helping to code this feature, sign up your name below:

  • YOU
  • RJ Ryan
  • Albert Santoni
Translations of this page:
n-deck_support.txt · Last modified: 2011/06/12 10:17 by engineer