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 metadata.map
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 metadata.map to s using append_title
s = metadata.map(append_title, s)
The effect of metadata.map
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 metadata.map
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 source with an added insert_metadata
method.
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 received 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 source with a `insert_metadata` method
s = insert_metadata(s)
# 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
s.insert_metadata([(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"