ableton-js

Ableton.js

Ableton.js lets you control your instance or instances of Ableton using Node.js. It tries to cover as many functions as possible.

This package is still a work-in-progress. My goal is to expose all of Ableton's MIDI Remote Script functions to TypeScript. If you'd like to contribute, please feel free to do so.

Prerequisites

To use this library, you'll need to install and activate the MIDI Remote Script in Ableton.js. To do that, copy the midi-script folder of this repo to Ableton's Remote Scripts folder. If you prefer, you can rename it to something like AbletonJS for better identification. The MIDI Remote Scripts folder is usually located at:

• Windows: {path to Ableton}\Resources\MIDI\Remote Scripts
• macOS: /Applications/Ableton Live {version}/Contents/App-Resources/MIDI Remote Scripts

After starting Ableton Live, add the script to your list of control surfaces:

If you've forked this project on macOS, you can also use yarn to do that for you. Running yarn ableton:start will copy the midi-script folder, open Ableton and show a stream of log messages until you kill it.

Using Ableton.js

This library exposes an Ableton class which lets you control the entire application. You can instantiate it once and use TS to explore available features.

Example:

import { Ableton } from "ableton-js";

const ableton = new Ableton();

const test = async () => {
  ableton.song.addListener("is_playing", p => console.log("Playing:", p));
  ableton.song.addListener("tempo", t => console.log("Tempo:", t));

  const cues = await ableton.get("cue_points");
  console.log(cues.map(c => c.raw));
};

test();

Protocol

Ableton.js uses UDP to communicate with the MIDI Script. Each message is a JSON object containing required data and a UUID so request and response can be associated with each other.

Compression and Chunking

To allow sending large JSON payloads, responses from the MIDI Script are compressed using gzip and chunked every 1024 bytes. The first byte of every message contains the chunk index (0x00-0xFF) followed by the gzipped chunk. The last chunk always has the index 0xFF. This indicates to the JS library that the previous received messages should be stiched together, unzipped, and processed.

Commands

A command payload consists of the following properties:

{
  "uuid": "a20f25a0-83e2-11e9-bbe1-bd3a580ef903", // A unique command id
  "ns": "song", // The command namespace
  "nsid": null, // The namespace id, for example to address a specific track or device
  "name": "get_prop", // Command name
  "args": { "prop": "current_song_time" } // Command arguments
}

The MIDI Script answers with a JSON object looking like this:

{
  "data": 0.0, // The command's return value, can be of any JSON-compatible type
  "event": "result", // This can be 'result' or 'error'
  "uuid": "a20f25a0-83e2-11e9-bbe1-bd3a580ef903"
}

Events

To attach an event listener to a specific property, the client sends a command object:

{
  "uuid": "922d54d0-83e3-11e9-ba7c-917478f8b91b", // A unique command id
  "ns": "song", // The command namespace
  "name": "add_listener", // The command to add an event listener
  "args": {
    "prop": "current_song_time", // The property that should be watched
    "eventId": "922d2dc0-83e3-11e9-ba7c-917478f8b91b" // A unique event id
  }
}

The MIDI Script answers with a JSON object looking like this to confirm that the listener has been attached:

{
  "data": "922d2dc0-83e3-11e9-ba7c-917478f8b91b", // The unique event id
  "event": "result", // Should be result, is error when something goes wrong
  "uuid": "922d54d0-83e3-11e9-ba7c-917478f8b91b" // The unique command id
}

From now on, when the observed property changes, the MIDI Script sends an event object:

{
  "data": 68.0, // The new value, can be any JSON-compatible type
  "event": "922d2dc0-83e3-11e9-ba7c-917478f8b91b", // The event id
  "uuid": null // Is always null and may be removed in future versions
}

Note that for some values, this event is emitted multiple times per second. 20-30 updates per second are not unusual.

Connection Events

The MIDI Script sends events when it starts and when it shuts down. These look like this:

{
  "data": null, // Is always null
  "event": "connect", // Can be connect or disconnect
  "uuid": null // Is always null and may be removed in future versions
}

When you open a new Project in Ableton, the script will shut down and start again.

When Ableton.js receives a disconnect event, it clears all current event listeners and pending commands. It is usually a good idea to attach all event listeners and get properties each time the connect event is emitted.

Findings

In this section, I'll note interesting pieces of information related to Ableton's Python framework that I stumble upon during the development of this library.

• It seems like Ableton's listener to output_meter_level doesn't quite work as well as expected, hanging every few 100ms. Listening to output_meter_left or output_meter_right works better. See Issue #4

Changelog

v1.10.1

29 May 2020

• :wrench: Update ports again because NTKDaemon uses them e581ada