Developer Guide Engine Player

Introduction to Mixxx's Deck/Sampler Processing

Perhaps the most complicated part of Mixxx lies in its player (decks, samplers, etc.) processing code. As the result of years worth of work by multiple, unconnected people there has been significant rot and just plain buggyness introduced over the years here. In recent years we have been steadily rewriting it to try and improve the situation but it is still quite complicated. This section of the developer guide aims to demystify this monolith a bit.

EngineBuffer

The lion's share of complexity lies in EngineBuffer. This class has the following responsibilities:

• Read decoded audio from a file loaded in the player.
• Keep track of the state of the player (whether it's playing, how fast it's playing, what direction it's playing)
• Respond to requests from elsewhere in Mixxx
• For example: seek to location, start/stop playing, seek to hotcue, start a beatloop, change the loop start/end position, eject track, etc.
• Re-sample audio from the native file sample-rate to the engine sample-rate.