streaming extempore

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Lately I’ve been playing with Extempore, an environment to play live music using Scheme and a DSL (xtlang) ; there are some cool screencasts on the web that convinced me it was what I wanted to try next. Unfortunately my laptop is too slow for this, so I wanted to use my server instead, which has a better CPU (audio processing is CPU bound).

The idea is to run Extempore inside a Docker container, connect the Extempore process to a Jack server with a dummy driver (as there’s no easy way to access the audio card from the container), and then, use VLC and its plugin for Jack to export the audio stream as HTTP.

The cool thing is that it becomes very easy to share what you are doing with friends: just open the HTTP link with a decent audio player (though in my case, it does not worth it). Also, you can easily having several performers from different places in the world hacking the current session at the same time.

I’ve dockerized everything so I can reuse this setup without trouble on other computers, also, if someone is interested in this approach, she/he can reuse without it burning too much time.

The workflow becomes:

  • start the Docker container,
  • start an audio player and connect to the live HTTP stream,
  • fire-up Emacs and connect to extempore,
  • have fun!

Here’s a quick guide to get your hands dirty, assuming you have a Linux with Docker installed:

Pull the Container

docker pull aimxhaisse/docker-extempore

Start the Docker Container

docker run -p 8080:8080 -p 7099:7099 aimxhaisse/docker-extempore

The Docker container has a virtual IP address which is accessible from the host, as I want to access the port 8080 (to listen) and the port 7099 (to connect my local emacs to extempore) from the outside, I publish these ports on the host interface.

Start an Audio Player

Quite straightforward:

cvlc http://mxs.sbrk.org:8080/

Connect to the Server

Nothing new here: ctrl+j to connect, specify the expected host, and that’s it.

Extra Notes

I plan to keep this Docker image up-to-date with the latest changes available on Extempore, if it appears to be a lie when you read this line, do not hesitate to drop me an e-mail.

Among the future changes that I might add:

  • Preloading of instruments.xtm to avoid waiting a few minutes before having funm
  • A tiny HTTP interface so it can be streamed using a recent web browser,
  • Probably some tuning on the outputed stream,
  • Some helpers to load samples (by sharing a directory with the container).