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”```