Packet Types

The protocol used by Pioneer professional DJ equipment to communicate and coordinate performances can be monitored to provide useful information for synchronizing other software, such as light shows and sequencers. By creating a “virtual CDJ” that sends appropriate packets to the network, other devices can be induced to send packets containing even more useful information about their state. This document details what has been learned so far about the protocol, and how to accomplish these tasks.

This information was discovered by studying packet captures and with the help of dysentery, a bespoke protocol analysis tool written in Clojure. This document was created in parallel with the development of dysentery to help spread the knowledge to other developers using other languages.

Once enough had been understood to start interacting in useful ways with the devices, the Beat Link library was written to provide a convenient interface for other programs running in the Java virtual machine. Eventually enough was learned about the format of the media databases on USB drives and SD cards inserted in the players to implement Crate Digger, another Java library which parses them, and whose analysis is part of this documentation site as well.

Other implementations include prolink-go and python-prodj-link.

Although there are occasionally TCP connections involved in the protocol, especially for track metadata queries, most of the features of the protocol are implemented through UDP packets sent to a handful of ports, often to the network broadcast address, but occasionally to individual devices. These are discussed in more detail in their individual sections, but here is a breakdown of the packet types which have been discovered so far.

DJ Link packets seem to all start with a fixed sequence of ten bytes, 51 73 70 74 31 57 6d 4a 4f 4c. This is followed by a byte which (combined with the port on which it was received) identifies what kind of information is found in the packet.