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+<body class="article">
+<div id="header">
+<h1>upmpdcli Linn Songcast integration</h1>
+</div>
+<div id="content">
+<div id="preamble">
+<div class="sectionbody">
+<div class="paragraph"><p>The <strong>upmdcli</strong> UPnP front-end to MPD implements support for Linn Songcast with
+help from the <strong>sc2mpd</strong> auxiliary process.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_what_is_songcast">What is Songcast</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>Songcast is a protocol for transporting audio streams across the
+network. This is independant from the UPnP framework which mostly deals
+with URLs and audio files (usually, but not necessarily, compressed).</p></div>
+<div class="paragraph"><p>The streams transported by Songcast are actual real-time audio data, which
+can go straight to an audio card for playing.</p></div>
+<div class="paragraph"><p>Controlling the streams (connecting, starting, stopping) is done through an
+UPnP service named OpenHome <em>Receiver</em>.</p></div>
+<div class="paragraph"><p>The typical use of Songcast is to have an audio driver on a Windows or OS X
+desktop capture and forward the audio stream to a remote Songcast device.</p></div>
+<div class="paragraph"><p>Any application on the desktop will (be compelled to) transparently play to
+the remote device, without need to know anything about Songcast.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_implementation_of_songcast_support_in_upmpdcli">Implementation of Songcast support in upmpdcli</h2>
+<div class="sectionbody">
+<div class="paragraph"><p><strong>upmpdcli</strong> implements the <em>Receiver</em> service, and uses an auxiliary process
+(<strong>sc2mpd</strong>) for transporting the audio data. <strong>sc2mpd</strong> is a slight
+modification of the sample program which comes with the Linn Songcast
+open-source implementation, with the addition of an HTTP interface (based
+on <em>libmicrohttpd</em>) to forward the data to <strong>mpd</strong>.</p></div>
+<div class="paragraph"><p>Setting up a connection happens as follows:</p></div>
+<div class="ulist"><ul>
+<li>
+<p>
+If it finds an executable <strong>sc2mpd</strong> command in the PATH when starting up,
+ <strong>upmpdcli</strong> advertises a <em>Receiver</em> service.
+</p>
+</li>
+<li>
+<p>
+The Songcast implementation from the desktop finds out about the
+ <em>Receiver</em> through the normal UPnP mechanisms and can be instructed to
+ use it. It then tells the <em>Receiver</em> in <strong>upmpdcli</strong> to start playing.
+</p>
+</li>
+<li>
+<p>
+<strong>upmdpcli</strong> starts the <strong>sc2mpd</strong> process, which gets ready to receive data
+ through Songcast, and make it available through HTTP.
+</p>
+</li>
+<li>
+<p>
+<strong>upmpdcli</strong> instructs <strong>mpd</strong> to play the URL for the <strong>sc2mpd</strong> output.
+</p>
+</li>
+</ul></div>
+<div class="paragraph"><p>There is currently a 10-12 S delay between the connection request and the
+moment the audio starts playing. This is not normal, but I could not find
+the reason for it, so it’s an unavoidable inconvenience at the moment.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_configuration">Configuration</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>No configuration is necessary: if <strong>sc2mpd</strong> is present, <strong>upmpdcli</strong> will
+advertise the Songcast capability, and any host with a Songcast sender
+installed should be able to use it.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_building_sc2mpd">Building sc2mpd</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>There are two parts in building <strong>sc2mpd</strong>:</p></div>
+<div class="ulist"><ul>
+<li>
+<p>
+Building the Openhome libraries
+</p>
+</li>
+<li>
+<p>
+Building <strong>scmpd</strong> proper
+</p>
+</li>
+</ul></div>
+<div class="paragraph"><p>Building the Openhome libraries is a bit of a black art, and the sc2mpd
+source comes with an <strong>ohbuild.sh</strong> script which will try to clone the
+Openhome git repositories and build the libs:</p></div>
+<div class="literalblock">
+<div class="content">
+<pre><tt>mkdir /my/place/for/openhome
+sh ohbuild.sh /my/place/for/openhome</tt></pre>
+</div></div>
+<div class="paragraph"><p>Miscellaneous error messages will be displayed during the build. Hope for
+the best…</p></div>
+<div class="paragraph"><p>When this is done configure sc2mpd:</p></div>
+<div class="literalblock">
+<div class="content">
+<pre><tt>sh autogen.sh
+./configure --prefix=/usr --with-openhome=/my/place/for/openhome
+make
+sudo make install</tt></pre>
+</div></div>
+<div class="paragraph"><p>The build uses static libraries, so you can move the executable to another
+machine without needing the openhome directory.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_miscellaneous_remarks">Miscellaneous remarks</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>Songcast is probably best transported over a wired connection. If you are
+doing this over WIFI and experiencing glitches, the wireless is the first
+suspect.</p></div>
+</div>
+</div>
+</div>
+<div id="footnotes"><hr /></div>
+<div id="footer">
+<div id="footer-text">
+Last updated 2014-11-09 15:51:29 CET
+</div>
+</div>
+</body>
+</html>