/usr/share/doc/liquidsoap/html/dynamic

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  <title>Liquidsoap :: Dynamic source creation</title>
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      <h1>Liquidsoap</h1>
      <h2>audio stream generation</h2>
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  <p>
Liquidsoap supports dynamic creation and destruction of sources 
during the execution of a script. The following gives an example
of this.
</p>
<p>
First some outlines:
</p>
<ul>
<li>
This example is meant to create a new source and outputs. It is not easy currently to change a source being streamed</li>
<li>
The idea is to create a new output using a telnet/server command.</li>
</ul>
<p>
In this example, we will register a command that creates a playlist source using an uri passed
as argument and outputs it to a fixed icecast output.
</p>
<p>
With more work on parsing the argument passed to the telnet command,
you may write more evolved options, such as the possibility to change
the output parameters etc..
</p>
<p>
Due to some limitations of the language, we have used some
intricate (but classic) functional programming tricks. They are
commented in order to help reading the code..
</p>
<p>
New here's the code:
</p>
<pre># First, we create a list referencing the dynamic sources:
dyn_sources = ref []

# This is our icecast output.
# It is a partial application: the source needs to be given!
out = output.icecast(%mp3,
                     host="test",
                     password="hackme",
                     fallible=true)

# Now we write a function to create 
# a playlist source and output it.
def create_playlist(uri) =
  # The playlist source 
  s = playlist(uri)

  # The output
  output = out(s)

  # We register both source and output 
  # in the list of sources
  dyn_sources := 
      list.append( [(uri,s),(uri,output)],
                    !dyn_sources )
  "Done!"
end

# And a function to destroy a dynamic source
def destroy_playlist(uri) = 
  # We need to find the source in the list,
  # remove it and destroy it. Currently, the language
  # lacks some nice operators for that so we do it
  # the functional way

  # This function is executed on every item in the list
  # of dynamic sources
  def parse_list(ret, current_element) = 
    # ret is of the form: (matching_sources, remaining_sources)
    # We extract those two:
    matching_sources = fst(ret)
    remaining_sources = snd(ret)

    # current_element is of the form: ("uri", source) so 
    # we check the first element
    current_uri = fst(current_element)
    if current_uri == uri then
      # In this case, we add the source to the list of
      # matched sources
      (list.append( [snd(current_element)], 
                     matching_sources),
       remaining_sources)
    else
      # In this case, we put the element in the list of remaining
      # sources
      (matching_sources,
       list.append([current_element], 
                    remaining_sources))
    end
  end
    
  # Now we execute the function:
  result = list.fold(parse_list, ([], []), !dyn_sources)
  matching_sources = fst(result)
  remaining_sources = snd(result)

  # We store the remaining sources in dyn_sources
  dyn_sources := remaining_sources

  # If no source matched, we return an error
  if list.length(matching_sources) == 0 then
    "Error: no matching sources!"
  else
    # We stop all sources
    list.iter(source.shutdown, matching_sources)
    # And return
    "Done!"
  end
end


# Now we register the telnet commands:
server.register(namespace="dynamic_playlist",
                description="Start a new dynamic playlist.",
                usage="start &lt;uri&gt;",
                "start",
                create_playlist)
server.register(namespace="dynamic_playlist",
                description="Stop a dynamic playlist.",
                usage="stop &lt;uri&gt;",
                "stop",
                destroy_playlist)
</pre>
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<a href="scripts/dynamic_playlist.liq">
<img class="grab" src="./images/grab.png" alt="Grab the code!">
</a>
</div></p>
<p>
If you execute this code (add a <code>output.dummy(blank())</code> if you have
no other output..), you have two new telnet commands:
</p>
<ul>
<li>
<code>dynamic_playlist.start &lt;uri&gt;</code></li>
<li>
<code>dynamic_playlist.stop &lt;uri&gt;</code></li>
</ul>
<p>
which you can use to create/destroy dynamically your sources.
</p>
<p>
With more tweaking, you should be able to adapt these ideas to your
precise needs.
</p>
<p>
If you want to plug those sources into an existing output, you may
want to use an <code>input.harbor</code> in the main output and change the
<code>output.icecast</code> in the dynamic source creation to send everything to
this <code>input.harbor</code>. You can use the <code>%wav</code> format in this case to avoid
compressing/decompressing the data..
</p>
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liquidsoap 1.0.0-4build1 / usr / share / doc / liquidsoap / html / dynamic_sources.html
