# Liquidsoap

## audio stream generation

### RadioPi

RadioPi is the web radio of the ECP (Ecole Centrale de Paris). RadioPi runs many channels. There are topical channels (Reggae, Hip-Hop, Jazz, ...). On top of that, they periodically broadcast live shows, which are relayed on all channels.

We met a RadioPi manager right after having released Liquidsoap 0.2.0, and he was seduced by the system. They needed quite complex features, which they were at that time fulfilling using dirty tricks, loads of obfuscated scripts. Using Liquidsoap now allow them to do all they want in an integrated way, but also provided new features.

##### The migration process

Quite easy actually. They used to have many instances Ices2, each of these calling a Perl script to get the next song. Other scripts were used for switching channels to live shows.

Now they have this single Liquidsoap script, no more. It calls external scripts to interact with their web-based song scheduling system. And they won new features: blank detection and distributed encoding.

The first machine gets its files from a ftp server opened on the second machine. Liquidsoap handles download automatically.

Each file is given by an external script, `radiopilote-getnext`, whose answer looks as follows (except that it's on a single line):

    annotate:file_id="3541",length="400.613877551",\
      type="chansons",display_title="John Holt - Holigan",\
      display_artist="RadioPi - Canal reggae",\
      display_album="Studio One SeleKta! - Album Studio 1 12",\
      canal="reggae":ftp://***:***@host/files/3541.mp3

Note that we use annotate to pass some variables to liquidsoap...

    #!/usr/bin/liquidsoap

    # Standard settings
    set("log.file.path","/var/log/liquidsoap/pi.log")
    set("init.daemon",true)
    set("log.stdout",false)
    set("log.file",true)
    set("init.daemon.pidfile.path","/var/run/liquidsoap/pi.pid")

    # Enable telnet server
    set("server.telnet",true)

    # Enable harbor for any external
    # connection
    set("harbor.bind_addr","0.0.0.0")

    # Verbose logs
    set("log.level",4)

    # We use the scheduler intensively,
    # therefore we create many queues.
    set("scheduler.generic_queues",5)
    set("scheduler.fast_queues",3)
    set("scheduler.non_blocking_queues",3)

    # === Settings ===

    # The host to request files
    stream = "XXXxXXXx"
    # The command to request files
    scripts = "ssh XXxxxXXX@#{stream} '/path/to/scripts/"
    # A substitution on the returned path
    sed = " | sed -e s#/path/to/files/#ftp://user:password@#{stream}/#'"

    # Enable replay gain
    enable_replaygain_metadata ()

    pass = "XXxXXXXx"
    ice_host = "localhost"

    descr = "RadioPi"
    url = "http://radiopi.org"

    # === Live ===

    # A live source, on which we stip blank (make the source
    # unavailable when streaming blank)
    live =
      strip_blank(
        input.harbor(id="live", port=8000, password=pass,
                     buffer=8.,max=20.,"live.ogg"),
        length=10., threshold=-50.)

    # This source relays the live data, when available,
    # to the other streamer, in uncompressed format (WAV)
    output.icecast(%wav, host=stream,
                   port=8005, password=pass,
                   mount="live.ogg", fallible=true,
                   live)

    # This source relays the live source to "live.ogg". This
    # is used for debugging purposes, to see what is sent
    # to the harbor source.
    output.icecast(%vorbis, host="127.0.0.1",
                   port=8080, password=pass,
                   mount="live.ogg", fallible=true,
                   live)

    # This source starts an archive of the live stream
    # when available
    title = '$(if $(title),"$(title)",\
             "Emission inconnue")$(if $(artist), \
             " par  $(artist)") - %m-%d-%Y, %H:%M:%S'
    output.file(%vorbis, reopen_on_metadata=true,
                fallible=true,
                "/data/archives/brutes/" ^ title ^ ".ogg",
                live)

    # === Channels ===

    # Specialize the output functions by partial application
    output.icecast = output.icecast(description=descr, url=url)
    out = output.icecast(host=ice_host,port=8080,password=pass,fallible=true)
    out_aac32 = out(%aacplus(bitrate=32))
    out_aac = out(%aacplus(bitrate=64))
    out = out(%mp3)

    # A file for playing during failures
    interlude =
      single("/home/radiopi/fallback.mp3")

    # Lastfm submission
    def lastfm (m) =
      if (m["type"] == "chansons") then
        if (m["canal"] == "reggae" or m["canal"] == "Jazz" or m["canal"] == "That70Sound") then
          canal =
            if (m["canal"] == "That70Sound") then
    	   "70sound"
    	else
    	   m["canal"]
    	end
          user = "radiopi-" ^ canal
          lastfm.submit(user=user,password="xXXxx",m)
        end
      end
    end

    # === Basic sources ===

    # Custom crossfade to deal with jingles..
    def smart_crossfade (~start_next=5.,~fade_in=3.,~fade_out=3.,
                         ~default=(fun (a,b) -> sequence([a, b])),
                         ~high=-15., ~medium=-32., ~margin=4.,
                         ~width=2.,~conservative=false,s)
      fade.out = fade.out(type="sin",duration=fade_out)
      fade.in  = fade.in(type="sin",duration=fade_in)
      add = fun (a,b) -> add(normalize=false,[b, a])
      log = log(label="smart_crossfade")

      def transition(a,b,ma,mb,sa,sb)

        list.iter(fun(x)-> log(level=4,"Before: #{x}"),ma)
        list.iter(fun(x)-> log(level=4,"After : #{x}"),mb)

        if ma["type"] == "jingles" or mb["type"] == "jingles" then
          log("Old or new file is a jingle: sequenced transition.")
          sequence([sa, sb])
        elsif
          # If A and B are not too loud and close, fully cross-fade them.
          a <= medium and b <= medium and abs(a - b) <= margin
        then
          log("Old <= medium, new <= medium and |old-new| <= margin.")
          log("Old and new source are not too loud and close.")
          log("Transition: crossed, fade-in, fade-out.")
          add(fade.out(sa),fade.in(sb))

        elsif
          # If B is significantly louder than A, only fade-out A.
          # We don't want to fade almost silent things, ask for >medium.
          b >= a + margin and a >= medium and b <= high
        then
          log("new >= old + margin, old >= medium and new <= high.")
          log("New source is significantly louder than old one.")
          log("Transition: crossed, fade-out.")
          add(fade.out(sa),sb)

        elsif
          # Opposite as the previous one.
          a >= b + margin and b >= medium and a <= high
        then
          log("old >= new + margin, new >= medium and old <= high")
          log("Old source is significantly louder than new one.")
          log("Transition: crossed, fade-in.")
          add(sa,fade.in(sb))

        elsif
          # Do not fade if it's already very low.
          b >= a + margin and a <= medium and b <= high
        then
          log("new >= old + margin, old <= medium and new <= high.")
          log("Do not fade if it's already very low.")
          log("Transition: crossed, no fade.")
          add(sa,sb)

        # What to do with a loud end and a quiet beginning ?
        # A good idea is to use a jingle to separate the two tracks,
        # but that's another story.

        else
          # Otherwise, A and B are just too loud to overlap nicely,
          # or the difference between them is too large and overlapping would
          # completely mask one of them.
          log("No transition: using default.")
          default(sa, sb)
        end
      end

      smart_cross(width=width, duration=start_next, conservative=conservative,
                  transition,s)
    end

    # Create a radiopilote-driven source
    def channel_radiopilote(~skip=true,name)
      log("Creating canal #{name}")

      # Request function
      def request () =
        log("Request for #{name}")
        ret = list.hd(get_process_lines(scripts^"radiopilote-getnext "^quote(name)^sed))
        log("Got answer: #{ret} for #{name}")
        request.create(ret)
      end

      # Create the request.dynamic source
      # Set conservative to true to queue
      # several songs in advance
      source =
        request.dynamic(conservative=true, length=400.,
                        id="dyn_"^name,request,
                        timeout=60.)

      # Apply normalization using replaygain
      # information
      source =   amplify(1.,override="replay_gain", source)

      # Skip blank when asked to
      source =
        if skip then
          skip_blank(source, length=10., threshold=-40.)
        else
          source
        end

      # Submit new tracks on lastfm
      source = on_metadata(lastfm,source)

      # Tell the system when a new track
      # is played
      source = on_metadata(fun (meta) ->
                        system(scripts ^ "radiopilote-feedback "
                               ^quote(meta["canal"])^" "
                               ^quote(meta["file_id"]) ^ "'"), source)

      # Rewrite metadata
      source =
        rewrite_metadata(
         [("artist",'$(if $(display_artist),"$(display_artist)","$(artist)")'),
          ("comment",""),
          ("title", '$(if $(display_title),"$(display_title)","$(title)")'),
          ("album", '$(if $(display_album),"$(display_album)","$(album)")')],
         source)

      # Finally apply a smart crossfading
      smart_crossfade(source)
    end

    # Basic source
    jazz = channel_radiopilote("jazz")
    discoqueen = channel_radiopilote("discoqueen")
    # Avoid skiping blank with classic music !!
    classique = channel_radiopilote(skip=false,"classique")
    That70Sound = channel_radiopilote("That70Sound")
    metal = channel_radiopilote("metal")
    reggae = channel_radiopilote("reggae")
    Rock = channel_radiopilote("Rock")

    # Group those sources in a seperate
    # clock (good for multithreading/multicore)
    clock.assign_new([jazz,That70Sound,metal,reggae])

    # === Mixing live ===

    # To create a channel from a basic source, add:
    # - a new-track notification for radiopilote
    # - metadata rewriting
    # - the live shows
    # - the failsafe 'interlude' source to channels
    # - blank detection
    def mklive(source) =
      # Transition function: if transitioning
      # to the live, fade out the old source
      # if transitioning from live, fade.in
      # the new source. NOTE: We cannot
      # skip the current song because
      # reloading new songs for all the
      # sources when live starts costs too much
      # CPU.
      def trans(old,new) =
        if source.id(new) == source.id(live) then
          log("Transition to live!")
          add([new,fade.final(old)])
        elsif source.id(old) == source.id(live) then
          log("Transitioning from live!")
          add([fade.initial(new),old])
        else
          log("Dummy transition")
          new
        end
      end
      fallback(track_sensitive=false,
        transitions=[trans,trans,trans],
        [live,source,interlude])
    end

    # Create a channel using mklive(), encode and output it to icecast.
    def mkoutput(~out=out,mount,source,name,genre)
      out(id=mount,mount=mount,name=name,genre=genre,
         mklive(source)
         )
    end

    # === Outputs ===

    mkoutput("jazz", jazz, "RadioPi - Canal Jazz","jazz")
    mkoutput("discoqueen", discoqueen, "RadioPi - Canal DiscoQueen","discoqueen")
    mkoutput("classique", classique, "RadioPi - Canal Classique","classique")
    mkoutput("That70Sound", That70Sound,
                           "RadioPi - Canal That70Sound","That70Sound")
    mkoutput("metal", metal, "RadioPi - Canal Metal","metal")
    mkoutput("reggae", reggae, "RadioPi - Canal Reggae","reggae")
    mkoutput("Rock", Rock, "RadioPi - Canal Rock","Rock")

    # Test outouts
    mkoutput(out=out_aac,"reggae.aacp", reggae, "RadioPi - Canal Reggae \
                                         (64 kbits AAC+ test stream)","reggae")
    mkoutput(out=out_aac32,"reggae.aacp32", reggae, "RadioPi - Canal Reggae \
                                          (32 kbits AAC+ test stream)","reggae")

The other machine has a similar configuration exept that files are local, but this is exactly the same for liquidsoap !

Using harbor, the live connects directly to liquidsoap, using port `8000` (icecast runs on port `8080`). Then, liquidsoap starts a relay to the other encoder, and both switch their channels to the new live.

Additionally, a file output is started upon live connection, in order to backup the stream. You could also add a relay to icecast in order to manually check what's received by the harbor.