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+<div id="header">
+<h1>Managing multiroom audio with Linn Songcast and upmpdcli</h1>
+</div>
+<div id="content">
+<div class="sect1">
+<h2 id="_what_is_linn_songcast">What is Linn Songcast</h2>
+<div class="sectionbody">
+<div class="paragraph"><p><strong>Songcast</strong> is a protocol for transporting audio streams across the network,
+developped by <a href="http://oss.linn.co.uk/trac/wiki/Songcast">Linn</a> as a
+series of open-source libraries and applications.</p></div>
+<div class="paragraph"><p>There are two types of entities involved in the protocol:</p></div>
+<div class="ulist"><ul>
+<li>
+<p>
+A <strong>Songcast</strong> <em>Sender</em> generates an audio stream.
+</p>
+</li>
+<li>
+<p>
+A <strong>Songcast</strong> <em>Receiver</em>, which typically runs on an OpenHome Renderer,
+ receives the stream and plays it.
+</p>
+</li>
+</ul></div>
+<div class="paragraph"><p>The streams transported by <strong>Songcast</strong> 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>, which runs on an
+UPnP Media Renderer implementing the OpenHome services.</p></div>
+<div class="paragraph"><p>The typical use of <strong>Songcast</strong> is to have an audio driver on a Windows or OS X
+desktop capture and forward the audio stream to a remote <strong>Songcast</strong> device
+(this is the main purpose of the <strong>Songcast</strong> Mac and Windows applications,
+apart from actually controlling the audio destination).</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 <strong>Songcast</strong>.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_multiple_receivers">Multiple Receivers</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>Multiple <em>Receiver</em> hosts can connect to the same <em>Sender</em>, so that they
+will all be playing the same audio.</p></div>
+<div class="paragraph"><p>The Mac and Windows <strong>Songcast</strong> apps only let you connect the <em>Sender</em> to one
+Receiver though.</p></div>
+<div class="paragraph"><p><strong>upmpdcli</strong> now includes a small application which can list the state of
+the local <strong>Songcast</strong> Receivers, make a Receiver play from the same URI as
+another one (for building multiroom groups), or return a Media Renderer
+from Receiver to normal operation.</p></div>
+<div class="paragraph"><p>The functions can be accessed either from the <strong>scctl</strong> command line utility,
+or from a local Web application (as Songcast is mostly used from a Windows
+or Mac PC, it would be inconvenient to have to access the Linux command
+line to control the multiroom groups).</p></div>
+<div class="paragraph"><p>This has only be tested with <strong>upmpdcli</strong> and its <a href="sc2mpd.html">sc2mpd</a>
+<strong>Songcast</strong> auxiliary process as Receiver implementation, but I’d guess that
+there is a good chance it would work with others.</p></div>
+<div class="paragraph"><p>This is very preliminary for now and there are a number of issues, I hope
+to improve them, but for now, this is definitely an <em>early adopters</em> system:</p></div>
+<div class="ulist"><ul>
+<li>
+<p>
+The initial synchronisation when forming the group is very bad. To
+ resynchronize everything, stop or pause the playing on the PC (from the
+ player, e.g. Media Player, not from the Songcast utility), wait for the
+ audio to drain, and a few seconds more, then restart playing.
+</p>
+</li>
+<li>
+<p>
+It’s quite easy to put the system in a confused state where nothing
+ seems to work any more. Stopping all Receivers (with <strong>scctl</strong> or the Web
+ interface) and restarting the PC will normally get things back to
+ sanity, but it will sometimes be necessary to restart everything.
+ <strong>Always give the commands a little time to take effect</strong>. Especially,
+ it’s quite common that the audio will not begin to play for around
+ 10 S after activation from the <strong>Songcast</strong> PC interface. Clicking on
+ stuff too early is the surest way to get into bad states, always give
+ 10 S to the system when things seem to not be happening.
+</p>
+</li>
+<li>
+<p>
+<em>The following problem seems to be gone from the latest <strong>Songcast</strong>
+ code</em> (which is used by the current <tt>ohbuild.sh</tt> script). Songcast can
+ be transported by either unicast or multicast IP. multicast is of
+ course much better for the network load, but I seem to have seen random
+ <strong>sc2mpd</strong> crashes with it. I am not sure of the cause (may be not linked
+ to multicast at all), but if you experience random <strong>sc2mpd</strong> crashes,
+ switch <strong>Songcast</strong> to unicast (in the PC Songcast app advanced
+ configuration panel. Unicast is the default).
+</p>
+</li>
+</ul></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_setting_things_up">Setting things up</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>The following seems to work for me:</p></div>
+<div class="ulist"><ul>
+<li>
+<p>
+Remove libupnpp and upmpdcli packages from the system to avoid confusion
+</p>
+</li>
+<li>
+<p>
+Clone the libupnpp, upmpdcli and sc2mpd repositories from
+ <a href="https://github.com/">GitHub</a>
+</p>
+</li>
+<li>
+<p>
+Follow the usual procedure to build. This should just be the usual for
+ libupnpp and upmpdcli:
+</p>
+<div class="literalblock">
+<div class="content">
+<pre><tt>sh autogen.sh
+./configure --prefix=/usr
+make
+sudo make install</tt></pre>
+</div></div>
+</li>
+<li>
+<p>
+For sc2mpd, things are a small bit more complicated, see the <em>Building
+ sc2mpd</em> section in <a href="sc2mpd.html">this document</a>.
+</p>
+</li>
+<li>
+<p>
+Repeat the above steps on all the machines which you want to be Receivers.
+</p>
+</li>
+<li>
+<p>
+Activate a Receiver from the PC <strong>Songcast</strong> interface. Play something and
+ leave it playing.
+</p>
+</li>
+<li>
+<p>
+Use either <strong>scctl</strong> (<tt>scctl -h</tt> prints a simple help message), or the Web
+ interface (see further) to associate other Receivers to the same Sender.
+</p>
+</li>
+<li>
+<p>
+Stop or Pause the music. Wait 10 S, restart. <strong><em>Multiroom !</em></strong>
+</p>
+</li>
+</ul></div>
+<div class="paragraph"><p>Once the slave Receivers are associated with the Sender, they should stay
+in this state until you change it. So you can stop/start Songcast on the
+PC, and they will usually just follow.</p></div>
+<div class="paragraph"><p>An "associated" Receiver is just one which plays from the same URI, it
+keeps no other relation to the "Master". Only one Receiver is a bit special
+because it is the one known from the PC, but there is no specific reason to
+use it as Master, the Master is only used to get the URI. Avoid changing
+the state of the "PC"l Receiver from outside the PC <strong>Songcast</strong> interface,
+this can only confuse things.</p></div>
+<div class="paragraph"><p>Every time you change the group configuration, you need to resynchronize
+the audio by pausing, waiting, restarting.</p></div>
+<div class="paragraph"><p>I do know that the whole thing is not very solid, this is a prototype and I
+hope to improve some of the issues in the future: constructive problem
+reports are more than welcome, but no flaming (for now) please :)</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_controlling_the_songcast_groups_from_the_web_interface">Controlling the Songcast groups from the Web interface</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>To avoid having to access the command line interface to control the
+<strong>Songcast</strong> groups, <strong>upmpdcli</strong> comes with a small Web server which uses
+<strong>scctl</strong> to actually do the work. This is found inside the <tt>web/</tt>
+subdirectory inside the <strong>upmpdcli</strong> source tree.</p></div>
+<div class="paragraph"><p>The server is based on the
+<a href="http://bottlepy.org/docs/dev/index.html">Bottle Python Web Framework</a>
+and it only depends on Python (version 2 and 3 are supported by <strong>Bottle</strong>,
+but the current app only works with Python 2).</p></div>
+<div class="paragraph"><p>I’ll find ways to autostart the server in the future, but for now,
+use the <tt>scweb-standalone.py</tt> script to manually start it:</p></div>
+<div class="literalblock">
+<div class="content">
+<pre><tt>python2 ./scweb-standalone.py</tt></pre>
+</div></div>
+<div class="paragraph"><p>This will start a server on localhost, on port 8777 which is good for
+testing, but not very useful. Use the -a 0.0.0.0 option to let the server
+answer on all local addresses (or specify the address to use a specific
+interface):</p></div>
+<div class="literalblock">
+<div class="content">
+<pre><tt>python2 ./scweb-standalone.py -a 0.0.0.0</tt></pre>
+</div></div>
+<div class="paragraph"><p>-p can be used to specify a port.</p></div>
+<div class="paragraph"><p>Once started, connecting to the server from any browser should hopefully
+display a reasonably self-explanatory interface.</p></div>
+</div>
+</div>
+</div>
+<div id="footnotes"><hr /></div>
+<div id="footer">
+<div id="footer-text">
+Last updated 2015-04-29 14:41:49 CEST
+</div>
+</div>
+</body>
+</html>