A loose connector for interacting with Ableton Link.

Carabiner is a program that embeds the C++ Link library and listens for local TCP connections to allow other programs, like beat-link-trigger and Afterglow, to participate in some aspects of a Link session, even though they were not written using C++ compatible languages and runtimes.

Carabiner does not support the full power and elegance of Link, so if you are writing a program that can use the library directly, you are much better off doing that instead. Carabiner is for cases where that is impossible or impractical.

If you are on a Mac OS X system, you can download the executable from the releases page. Then just open a terminal window, and run it:

> Carabiner
Starting Carabiner on port tcp:https://127.0.0.1:17000
Link bpm: 128.5 Peers: 1 Connections: 0

By default it listens on port 17000. If this port is already in use on your system, you can specify a different port using the --port command-line argument.

The status line shows the current tempo of the Link session, and the number of Link Peers which have been found. It also shows how many TCP connections are currently open to Carabiner from client programs like beat-link-trigger. See the documentation of the client program for instructions on how to have it connect to Carabiner.

You can shut down Carabiner by typing Control-C in the Terminal window, or simply closing that window.

If you want to run Carabiner on a different platform, or make and test modifications to its source code, you can build it yourself.

Carabiner relies on link and gflags as git submodules (and link relies on its own submodules), so after you have cloned the main carabiner repository, you need to cd into it and set up the submodules by running:

git submodule update --init --recursive

Carabiner uses CMake to manage its build process. Once again, from the top-level directory of your carabiner repository:

mkdir build
cd build
cmake ..
cmake --build .

Once the build completes you will find the executable in bin/Carabiner under the build directory.

Client programs interact with Carabiner by sending and receiving simple single-packet messages. The currently supported messages are:

Sending the string status to Carabiner requests an update containing the current status. It will respond with a packet like the following:

status { :peers 1 :bpm 128.500019 :start 128928334480 :beat 106.412459 }

As with all non-error messages from Carabiner, this consists of a message type identifier followed by an edn structure containing the message parameters. In this case, it identifies the current number of Link peers, the current tempo of the Link session, the timestamp of when the session timeline started, and the current beat position.

A status response will also be sent when you first connect to Carabiner, and whenever the Link session tempo changes, as well as whenever the number of Link peers changes.

Sending the string bpm followed by a floating-point value, for example bpm 140.0, tells Carabiner to immediately set the Link session's tempo to the specified value. If this is a change from the previous value, it will result in a status response as described above.

If the bpm value is missing, cannot be parsed as a floating point number, or is outside the range from 20.0 to 999.0, the session tempo is left unchanged and Carabiner responds with the message bad-bpm followed by the argument you supplied.

If your client wants to use a tempo outside the range supported by Link, Ableton recommends setting the Link tempo to the closest multiple or fraction which is in range. For example, if the user wants 15 BPM, set the session tempo to 30 BPM.

Sending the string beat-at-time followed by a nanosecond timestamp (an integer relative to the :start value returned in the status response), and a quantum value (which identifies the number of beats that make up a bar or loop as described in the Phase Synchronization section of the Link documentation), asks Carabiner to identify the beat which falls at the specified point on the Link session timeline. For example, sending beat-at-time 129426900000 4 to the link session used in the above examples would result in a response like the following:

beat-at-time { :when 129426900000 :quantum 4.000000 :beat 1.278066 }

This response indicates that at the specified nanosecond along the Link session timeline, we are just over a quarter of the way from the second to the third beat.

If one of the parameters is missing or cannot be parsed, Carabiner responds with bad-time or bad-quantum followed by the arguments you gave it.

Sending the string force-beat-at-time followed by a floating-point beat number, a nanosecond timestamp (an integer relative to the :start value returned in the status response), and a quantum value (as described above) tells Carabiner to forcibly and abruptly adjust the Link session timeline so that the specified beat falls at the specified point in time. The change will be communicated to all participants, and will result in audible shifts in playback.

Continuing the previous example, sending force-beat-at-time 1.0 129426900000 4 will tell Carabiner to adjust the Link session timeline so the second beat starts as close as possible to the specified moment (which previously was 28% of the way to the third beat). Carabiner responds with a status message which reports the new :start timestamp of the timeline.

status { :peers 1 :bpm 140.000000 :start 129426471429 :beat 115.286846 }

At this point, repeating the beat-at-time command from the previous section will return a beat value that is very close to 1.0.

beat-at-time { :when 129426900000 :quantum 4.000000 :beat 0.999984 }

If one of the parameters is missing or cannot be parsed, Carabiner responds with bad-beat , bad-time , or bad-quantum followed by the arguments you gave it.

This command should only be used when synchronizing a Link session to an external timing source which cannot participate in the consensus-based Link timeline, and should be done only when the session has drifted beyond some reasonable threshold, so that external jitter does not lead to excessive adjustments.

If you are building an application that can perform quantized starts, and thereby participate in a Link session more graciously, without requiring the other participants to shift the timeline, then open an issue to have the request-beat-at-time command implemented by Carabiner.

I am not a C++ programmer; the last time I wrote anyting in it before Carabiner was in the early 1990s. This seems to work, but I am sure it could be written much better. Suggestions for improvement are definitely welcome!

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http:https://www.gnu.org/licenses/.

Link and Mongoose are dual-licensed. While available through the same GPL v2 as Carabiner itself, they are also available through proprietary licenses for embedding in non-free software, by contacting their respective developers.

gflags is Copyright © 2006, Google Inc. It has its own license.