Liquidsoap

Website	http://liquidsoap.info/
License	GPL
OS	GNU/Linux, OS X, Windows
Media	Streaming media
Format	OGG, MP3
Interface	Custom programming language
Wikipedia	http://en.wikipedia.org/wiki/Draft:Liquidsoap
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Cookbook

From: https://www.liquidsoap.info/doc-1.4.2/cookbook.html

The recipes show how to build a source with a particular feature. You can try short snippets by wrapping the code in an out(..) operator and passing it directly to liquidsoap:

 liquidsoap -v 'out(recipe)'

For longer recipes, you might want to create a short script:

#!/usr/bin/liquidsoap -v

set("log.file.path","/tmp/<script>.log")
set("log.stdout",true)

recipe = # <fill this>
out(recipe)

See the quickstart guide for more information on how to run Liquidsoap, on what is this out(..) operator, etc.

Sound processing

liquidsoap can be used to process / filter sound either in a streaming pipeline, or used "offline" to directly produce an audio output (file).

See https://www.liquidsoap.info/doc-1.4.2/reference.html#source-sound-processing

Links / Projects / Radio streams that use liquidsoap

Data Radio. Here a script created a day and night playlist, with a "fallback" to allow a live stream to interrupt.

playlist

playlist source

mode (of type string, which defaults to "randomize"): Play the files in the playlist either in the order (“normal” mode), or shuffle the playlist each time it is loaded, and play it in this order for a whole round (“randomize” mode), or pick a random file in the playlist each time (“random” mode).

say_metadata

say_metadata filter

outputs

Basic outputs of interest:

out which is the shortcut for output.preferred: play to the soundcard directly (if possible)
output.file: play to a file
output.icecast Send audio to an icecast server

examples

liquidsoap 'out(noise())'

liquidsoap 'out(playlist("playlist.pls"))'
liquidsoap 'output.prefered(mksafe(playlist("playlist.pls")))'
liquidsoap 'output.file(%mp3,"output.mp3",mksafe(playlist("playlist.pls")))'

with playlist.pls:

brown.ogg

Observations:

WAV files don't seem to work, but ogg + mp3 seem OK! (or was this the stereo problem)
explicit output modules (like output.file) seem to require the use of mksafe (out doesn't need this).

Doesn't work with mono source material -- default seems to be stereo...

  [decoder:3] Unable to decode "./speech0001.mp3" as {audio=2;video=0;midi=0}!
  2020/05/11 17:42:04 [decoder.mad:3] File "./speech0003.mp3" has an incompatible number of channels.

  WAV file "speech0001.wav" has content type {audio=1;video=0;midi=0} but {audio=2;video=0;midi=0} was expected.

How would you output a mono audio stream?