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<body class="article">
<div id="header">
<h1>sc2mpd: helper for upmpdcli Songcast support</h1>
</div>
<div id="content">
<div id="preamble">
<div class="sectionbody">
<div class="paragraph"><p>The <strong>sc2mpd</strong> auxiliary process implements part of Linn <strong>Songcast</strong> support
for the <strong>upmdcli</strong> UPnP MPD front-end. Specifically, it implements a
<strong>Songcast</strong> <em>Receiver</em> service, managed by <strong>upmpdcli</strong>.</p></div>
<div class="paragraph"><p>To use it, you need the
<a href="http://www.linn.co.uk/software#songcast">Linn Songcast application</a>
installed on a Microsoft Windows or Apple Mac OS X PC. See
<a href="#whatis_songcast">further</a> for more explanations about what this does.
Not all Songcast versions work well with upmpdcli. Lately I’ve had good
luck with
<a href="http://oss.linn.co.uk/Releases/Songcast/Davaar/Songcast_4.4.190_win.exe">4.4.190</a>
but not with the 4.5 ones.</p></div>
<div class="paragraph"><p>Warning: <strong>there is no software volume control</strong> of the Songcast Receivers
for now: use either a local mixer or the little round things on the power
amps. Set it low when experimenting !</p></div>
<div class="paragraph"><p>There are Debian Wheezy <strong>sc2mpd</strong>
packages in the <strong>upmpdcli</strong> repository for i386, amd64 and Raspberry Pi
(Raspbian): see the <a href="downloads.html">upmpdcli download page</a>, so you do
not need to build any software if you use these systems.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">you know what Songcast is and have a Rasberry PI which wants to play:
<a href="#rpi_quick">quick install for the Raspberry PI</a> (also works for i386
and amd64 Debian Wheezy).</td>
</tr></table>
</div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">this does not work too well on Raspberry Pis using an USB DAC (YMMV
of course). As far as I can see the data rate of the uncompressed stream is
just too much for the poor Pi Ethernet/USB chip. Things work just fine with
an I2S DAC (or on HDMI I suppose).</td>
</tr></table>
</div>
</div>
</div>
<div class="sect1">
<h2 id="whatis_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>The protocol links two types of entities:</p></div>
<div class="ulist"><ul>
<li>
<p>
A <strong>Songcast</strong> <em>Sender</em> generates an audio stream (Windows or Mac).
</p>
</li>
<li>
<p>
<strong>Songcast</strong> <em>Receivers</em> receive and play the stream.
</p>
</li>
</ul></div>
<div class="paragraph"><p>There are <strong>Songcast</strong> applications (<em>Senders</em>) for Windows and Mac OS X
(nothing for Linux, iOS or Android for now). The <strong>Songcast</strong> application
captures and forward the system audio stream to a remote <strong>Songcast</strong>
<em>Receiver</em>.</p></div>
<div class="paragraph"><p><strong>Any</strong> application on the desktop (Windows Media Player, Spotify, Tidal,
etc.) will transparently play to the remote device, without any need to
know about <strong>Songcast</strong>. <strong><em>Any</em></strong> audio service available on Windows or the
Mac can be forwarded to one or <a href="scmulti.html">many</a> audio players around
the house.</p></div>
<div class="paragraph"><p>The <strong>Songcast</strong> streams are 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 (e.g. <strong>upmpdcli</strong>).</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</p></div>
<div class="paragraph"><p><strong>sc2mpd</strong> can play the audio stream in two modes:</p></div>
<div class="ulist"><ul>
<li>
<p>
By offering a local HTTP interface (based on <em>libmicrohttpd</em>) from which
<strong>mpd</strong> will play the stream.
</p>
</li>
<li>
<p>
By directly using the <strong>alsa</strong> audio driver.
</p>
</li>
</ul></div>
<div class="paragraph"><p>What approach is used is decided by a parameter in the upmpdcli
configuration file: <code>scplaymethod</code> (see <a href="#Configuration">[Configuration]</a> further)</p></div>
<div class="paragraph"><p>Control:</p></div>
<div class="ulist"><ul>
<li>
<p>
If <strong>upmpdcli</strong> finds an executable <strong>sc2mpd</strong> command in the PATH when
starting up, it advertises a <em>Receiver</em> service.
</p>
</li>
<li>
<p>
The <strong>Songcast</strong> application on 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 either play it directly or make it available
through HTTP.
</p>
</li>
<li>
<p>
If the <em><code>mpd</code></em> method is in use, <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>When using <em><code>mpd</code></em> more bufferisation occurs and there may be a significant
delay (up to around 10S) between the time when Songcast is activated and
the time sound appears.</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
NOTE
</dt>
<dd>
<p>
When using <em><code>mpd</code></em>, from a Mac (24 bits audio) you need <strong>mpd 0.19</strong>,
configured with <code>--disable-audiofile</code>, else you risk producing high volume
noise. As Debian and Ubuntu tend to lag quite bit on MPD progresses, I
have set up <a href="downloads.html#mpd">backport repositories</a> for
appropriately configured recent mpd versions (currently 0.19.9), for
Ubuntu, Debian i386/amd64 and Raspbian.
</p>
</dd>
</dl></div>
<div class="paragraph"><p>Given the bufferisation and delay control issues when going through MPD,
only the <em><code>alsa</code></em> method is usable in multi-room configurations. Even with a
single player, the <em><code>mpd</code></em> method will experience skips from time to
time. The reasons are explained in the <a href="scmulti.html">multi-room</a>
page.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="rpi_quick">Quick install for Debian Wheezy systems</h2>
<div class="sectionbody">
<div class="paragraph"><p>There are packages available for Raspbian and Debian Wheezy i386 and amd64.</p></div>
<div class="paragraph"><p>So add the repositories:</p></div>
<div class="literalblock">
<div class="content">
<pre><code>echo deb http://www.lesbonscomptes.com/upmpdcli/downloads/debian/ unstable main | sudo tee /etc/apt/sources.list.d/upmpdcli.list
echo deb-src http://www.lesbonscomptes.com/upmpdcli/downloads/debian/ unstable main | sudo tee -a /etc/apt/sources.list.d/upmpdcli.list
echo deb http://www.lesbonscomptes.com/upmpdcli/downloads/mpd-debian/ unstable main | sudo tee -a /etc/apt/sources.list.d/upmpdcli.list
echo deb-src http://www.lesbonscomptes.com/upmpdcli/downloads/mpd-debian/ unstable main | sudo tee -a /etc/apt/sources.list.d/upmpdcli.list</code></pre>
</div></div>
<div class="paragraph"><p>Install (the mpd and libupnp versions in the repo have bug fixes):</p></div>
<div class="literalblock">
<div class="content">
<pre><code>sudo apt-get update
sudo apt-get install upmpdcli sc2mpd mpd libupnp6</code></pre>
</div></div>
<div class="paragraph"><p>And see the next section for configuring.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="Configuration">Configuration</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_on_the_receiver_side">On the Receiver side</h3>
<div class="paragraph"><p>No configuration is necessary by default: 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 class="paragraph"><p>However, you can set a number of values in the upmpdcli configuration file
(you <strong>must</strong> set the <strong>upmpdcli</strong> <code>-c</code> option for <strong>sc2mpd</strong> to see them, the
environment variable will not work):</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
sclogfilename
</dt>
<dd>
<p>
Name of the file which will receive <strong>sc2mpd</strong> log messages. <code>stderr</code> by
default. This <em>can’t be</em> the same file used by <strong>upmpdcli</strong>.
</p>
</dd>
<dt class="hdlist1">
scloglevel
</dt>
<dd>
<p>
Log verbosity.
</p>
</dd>
<dt class="hdlist1">
scplaymethod
</dt>
<dd>
<p>
Used by <strong>upmpdcli</strong> and <strong>sc2mpd</strong>. This decides how audio is played, with 2
possible values, <em><code>alsa</code></em> or <em><code>mpd</code></em>. Using <em><code>mpd</code></em> is somewhat easier, but
unusable in <a href="scmulti.html">multi-room</a> configurations, and you risk
small drops even in single-player settings.
</p>
</dd>
<dt class="hdlist1">
scalsadevice
</dt>
<dd>
<p>
If the <em><code>alsa</code></em> method is set, the <code>scalsadevice</code>
parameter defines the interface name. Use <code>aplay -L</code> to find the
appropriate name. Also check that user <em><code>upmpdcli</code></em> belongs to the
<em><code>audio</code></em> group.
</p>
</dd>
<dt class="hdlist1">
sccvttype
</dt>
<dd>
<p>
If the <em><code>alsa</code></em> play method is used, this defines the libsamplerate
converter type. See <a href="http://www.mega-nerd.com/SRC/api_misc.html#Converters">http://www.mega-nerd.com/SRC/api_misc.html#Converters</a>.
The default is to use SRC_CVT_FASTEST, resulting in around 24% CPU usage
for sc2mpd processing a 16 bits stream on a Raspberry Pi 1. The value can
be specified either as a string (e.g SRC_SINC_FASTEST), or a value (e.g 2).
</p>
</dd>
<dt class="hdlist1">
schttpport
</dt>
<dd>
<p>
If the <em><code>mpd</code></em> method is set, this defines the HTTP port used by <strong>mpd</strong> to
connect to <strong>sc2mpd</strong>. 8768 by default. This must be an available port on
<code>localhost</code>, and it will only accept connections from <code>localhost</code>.
</p>
</dd>
<dt class="hdlist1">
sc2mpd
</dt>
<dd>
<p>
Used by <strong>upmpdcli</strong>. Path for the <strong>sc2mpd</strong> executable file
(e.g. <code>/usr/local/bin/sc2mpd</code>). Only useful if <strong>sc2mpd</strong> was not installed
to a location in the executable $PATH set for the init scripts. Typically
only <code>/bin</code> and <code>/usr/bin</code> are in there. This allows <strong>upmpdcli</strong> to find
<strong>sc2mpd</strong> if it is not in the standard location.
</p>
</dd>
</dl></div>
</div>
<div class="sect2">
<h3 id="_on_the_sender_windows_mac_side">On the Sender (Windows/Mac) side</h3>
<div class="paragraph"><p>Not all versions of Songcast work well with sc2mpd. Lately, I have had good
luck with 4.4.190, but not 4.5.298. You will find
<a href="http://oss.linn.co.uk/Releases/Songcast/Davaar/">all the Songcast installers
here</a></p></div>
<div class="paragraph"><p>I could not get IP multicast to work with WIFI Receivers (the sound drops
constantly).</p></div>
<div class="paragraph"><p>There are well-known problems with multicast and WIFI (see for example
<a href="http://superuser.com/questions/730288/why-do-some-wifi-routers-block-multicast-packets-going-from-wired-to-wireless">this
superuser.com question</a>
for detailed explanations). This seems to be dependant on the WIFI hardware
(router/access points) used, so maybe you will have more luck than me.</p></div>
<div class="paragraph"><p>If some of your Receivers use WIFI, and you experience sound issues, check
that "Unicast" is selected in the Songcast configuration "advanced" panel
on the desktop.</p></div>
<div class="paragraph"><p>Under most conditions, WIFI data rates should be more than sufficient to
transport Songcast streams (a bit over 1 Mbit/S for 48k/24bits, 700 Kbits/S
for 44.1k/16 bits).</p></div>
</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>sc2mpd</strong> proper
</p>
</li>
</ul></div>
<div class="paragraph"><p>First download a
<a href="http://www.lesbonscomptes.com/upmpdcli/downloads.html"><strong>sc2mpd</strong>
release</a> or clone the <strong>sc2mpd</strong>
<a href="http://www.github.com/medoc92/sc2mpd">Github repository</a>.</p></div>
<div class="paragraph"><p><strong>sc2mpd</strong> depends on a number of libraries:</p></div>
<div class="ulist"><ul>
<li>
<p>
The <a href="http://www.gnu.org/software/libmicrohttpd/">microhttpd</a>
library. Install the development and runtime packages which are currently
named <em>libmicrohttpd-dev</em> and <em>libmicrohttpd10</em> on Debian-derived systems
(use <em>libmicrohttpd</em> and <em>libmicrohttpd-devel</em> for Fedora).
</p>
</li>
<li>
<p>
The <a href="http://www.mega-nerd.com/SRC/">libsamplerate</a>
library. <em>libsamplerate0</em> on debian-derived systems.
</p>
</li>
<li>
<p>
The <strong>libasound</strong> Alsa interface library (<em>libasound2</em>).
</p>
</li>
</ul></div>
<div class="paragraph"><p>Building the Openhome libraries is a bit of a black art, and the <strong>sc2mpd</strong>
source comes with an <em>ohbuild.sh</em> script which will try to clone the
Openhome Git repositories and build the libs:</p></div>
<div class="literalblock">
<div class="content">
<pre><code>cd sc2mpd
mkdir /my/place/for/openhome
sh ohbuild.sh /my/place/for/openhome</code></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, build <strong>sc2mpd</strong>, using the following commands inside the
<em>sc2mpd</em> directory:</p></div>
<div class="literalblock">
<div class="content">
<pre><code>sh autogen.sh
./configure --prefix=/usr --with-openhome=/my/place/for/openhome
make
sudo make install</code></pre>
</div></div>
<div class="paragraph"><p>The build uses static Openhome libraries, so you can move the executable to
another machine without needing the Openhome directory (don’t forget to
install the <em>libmicrohttpd</em>, <em>libsamplerate</em> and <em>libasound</em> runtimes
though).</p></div>
<div class="paragraph"><p>After restarting <strong>upmpdcli</strong>, it should advertise the <em>Receiver</em> service and
appear in the Songcast Sender menus.</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
2015-12-15 21:18:51 CET
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