Customize metadata using Liquidsoap
Liquidsoap has several mechanism for manipulating the metadata attached to your stream. In this page we quickly detail and compare the different operators, see the language reference for full details about them.
Warning. The protocol used by Shoutcast and Icecast before version 2 does
not support many fields. It mainly support one: song. So, if you
need to customize the metadata displayed by these servers, you should
customize only the song metadata.
The annotate protocol
The metadata are read from files, so the most simple way is to properly tag the
files. However, if it not possible to modify the files for some reason, the
annotate protocol can be used in playlists to insert and modify some
metadata. For instance, in the playlist
annotate:title="Title 1",artist="Artist 1":music1.mp3 annotate:title="Title 2",artist="Artist 2":music2.mp3
the title metadata for file music1.mp3 will be overridden and changed to “Title 1” (and similarly for the artist).
Map metadata
The map_metadata operator applies a specified function to transform
each metadata chunk of a stream. It can be used to add or decorate metadata, but
is also useful in more complex cases.
A simple example using it:
# A function applied to each metadata chunk
def append_title(m) =
# Grab the current title
title = m["title"]
# Return a new title metadata
[("title","#{title} - www.station.com")]
end
# Apply map_metadata to s using append_title
s = map_metadata(append_title, s)
The effect of map_metadata by default is to update the metadata with the
returned values. Hence in the function append_title defined in the code above
returns a new metadata for the label title and the other metadata remain
untouched. You can change this by using the update option, and you can also
remove any metadata (even empty one) using the strip option.
See the documentation on map_metadata for more details.
Insert metadata
Using the telnet server
This operator is used for inserting metadata using a server command. If you have
an server.insert_metadata node named ID in your configuration, as in
server.insert_metadata(id="ID", source)
you can connect to the server (either telnet or socket) and execute commands like
ID.insert key1="val1",key2="val2",...
In Liquidsoap
Sometimes it is desirable to change the metadata dynamically when an event
occurs. In this case, the function insert_metadata (not to be confused with
server.insert_metadata above) can be used: when applied to a source it returns
a pair constituted of a function to update metadata and the source with inserted
metadata.
For instance, suppose that you want to insert metadata on the stream using the
OSC protocol. When a pair of strings “title” “The new title” is recieved on
/metadata, we want to change the title of the stream accordingly. This can be
achieved as follows.
# Our main music source
s = playlist("...")
s = mksafe(s)
# Create a function to insert metadata
ms = insert_metadata(s)
# The function to insert metadata
imeta = fst(ms)
# The source with inserted metadata
s = snd(ms)
# Handler for OSC events (gets pairs of strings)
def on_meta(m) =
# Extract the label
label = fst(m)
# Extract the value
value = snd(m)
# A debug message
print("Insert metadata #{label} = #{value}")
# Insert the metadata
imeta([(label,value)])
end
# Call the above handler when we have a pair of strings on /metadata
osc.on_string_pair("/metadata",on_meta)
# Output on icecast
output.icecast(%mp3,mount="test.mp3",s)
We can then change the title of the stream by sending OSC messages, for instance
oscsend localhost 7777 "/metadata" ss "title" "The new title"