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<html>
<head>
<title>libao - Documentation</title>
<link rel=stylesheet href="style.css" type="text/css">
</head>
<body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff">
<table border=0 width=100%>
<tr>
<td><p class=tiny>libao documentation</p></td>
<td align=right><p class=tiny>libao version 1.0.0 - 20100325</p></td>
</tr>
</table>
<h1>libao Drivers</h1>
<p>
Libao supports both <i>live</i> output drivers and <i>file</i> output
drivers. Live output drivers send audio data to sound cards and sound
daemons. File output drivers write audio to disk using a particular
file format (such as WAV, AU, etc.). You must invoke the
ao_open_????() function that corresponds to the type of driver you are
using, but otherwise live and file drivers are treated identically in
libao.
<p>Driver options may be passed to the drivers via the
<tt>*options</tt> argument to <a
href="ao_open_live.html">ao_open_live()</a> and <a
href="ao_open_file.html">ao_open_file()</a>, or they may be set in the
<a href="config.html">configuration file</a> as <tt>name=value</tt>
pairs.
<h2>Options understood by all Drivers</h2>
<ul>
<li>"debug" - (value not required) Requests driver print detailed
debugging information.
<li>"matrix" - Set an output channel mapping similar to the use of the
<i>matrix</i> field in <a
href="ao_sample_format.html">ao_sample_format</a>. The specified
matrix overrides the backend's native channel ordering/numbering. The
channel numbering used by the driver does not necessarily reflect the
physical ordering; for example, the fourth PulseAudio channel is
always 'Center' by default whether the channel physically exists or not.
<li>"quiet" - (value not required) Requests the driver print no output
whatsoever, even in the event of error.
<li>"verbose" - (value not required) Requests that the driver print
more detailed information concerning normal operation.
</ul>
<h2>Live Output Drivers</h2>
<h3>aixs</h3>
IBM AIX sound driver. According to the author, "tested on AIX 5.1 with
the Crystal chipsets only (found as internal audio in the 7043-140 and
on the MCA adapter DFE5 (7-6)), but it should work with other AIX
releases and the ACPA also."
<p>
<b>Option keys:</b>
<ul>
<li>"dev" - The audio device for the sound card. By default, the
driver tries "/dev/baud0/1" (device for MCA machines with the Crystal
chipset). Other possible devices are "/dev/paud0/1" for PCI machines
with the Crystal chipset, and "/dev/acpa0/1" for MCA machines with the
ACPA.
</ul>
<p>
<hr width="50%">
<h3>alsa</h3>
Advanced Linux Sound Architecture (API versions 0.9.x/1.x.x; earlier
API versions are now deprecated).
<p>
<b>Option keys:</b>
<ul>
<li>"buffer_time" - Override the default hardware buffer size (in
milliseconds).
<li>"dev" - ALSA device label to use. Examples include "hw:0" for the
first soundcard and "hw:1" for the second. The alsa driver normally
chooses one of "surround71", "surround51", "surround40" or "default"
automatically depending on number of output channels.
<li>"period_time" - Override the default hardware period size (in
microseconds).
<li>"use_mmap" - set to "yes" or "no" to override the compiled-in
default to use or not use mmap device access. In
the past, some buggy alsa drivers have behaved
better when not using mmap access at the penalty
of slightly higher CPU usage.
</ul>
<p>
<hr width="50%">
<h3>arts</h3>
aRts Sound Daemon live output driver.
<p>
<b>Option keys:</b>
<ul>
<li>"multi" - set to "yes" to allow opening the aRts playback device
for multiply concurrent playback. Although the driver works properly
in multi mode, it is known to occasionally crash the aRts server
itself. Default behavior is "no".
</ul>
<p>
<hr width="50%">
<h3>esd</h3>
ESounD audio driver. Although declining in poularity, this sound
daemon is still used on some Linux systems. It permits multiple
programs to play sound simultaneously and sound to be sent to
networked computers.
<p>
<b>Option keys:</b>
<ul>
<li>"host" - The hostname where esd is running. By default sound is
played on the local host. A port number can be specified after a
colon, as in "whizbang.com:555".
</ul>
<p>
<hr width="50%">
<h3>irix</h3>
IRIX audio driver. This was inherited from the original
libao, but has not been tested. Use at your own risk. (Better yet,
fix it! I don't have access to an IRIX system.)
<p>
<hr width="50%">
<h3>macosx</h3>
MacOS X AUHAL live output driver. This driver supports MacOS X 10.5
and later (10.4 and earlier uses an earlier, incompatable interface).
<p>
<b>Option keys:</b>
<ul>
<li>"buffer_time" - Set the hardware buffer size to the equivalent of
value milliseconds.
</ul>
<p>
<hr width="50%">
<h3>nas</h3>
Network Audio System live output driver.
<p>
<b>Option keys:</b>
<ul>
<li>"buf_size" - Set size of audio buffer on server in bytes.
<li>"host" - Set location of NAS server; See nas(1) for format.
</ul>
<p>
<hr width="50%">
<h3>null</h3>
Null driver. This is just a test device which does not write the
audio data anywhere.
<p>
<hr width="50%">
<h3>oss</h3>
Open Sound System driver. This is the audio system for
older Linux and FreeBSD as well as some other UNIX-like systems.
<p>
<b>Option keys:</b>
<ul>
<li>"dsp" - The dsp device. By default, the driver tries
"/dev/sound/dsp", followed by "/dev/dsp".
</ul>
<p>
<hr width="50%">
<h3>pulse</h3>
PulseAudio live audio sound driver. Pulse is a sound server daemon
used by the modern Gnome desktop on UNIX-like systems.
<p>
<b>Option keys:</b>
<ul>
<li>"server" - Specifies Pulseaudio server to use.
<li>"sink" - Specifies Pulseaudio sink to use.
</ul>
<p>
<hr width="50%">
<h3>roar</h3>
Roar Audio live audio sound driver.
<p>
<b>Option keys:</b>
<ul>
<li>"host" - Specifies Roar server to use.
</ul>
<p>
<hr width="50%">
<h3>sndio</h3>
SNDIO is the modern audio interface used by OpenBSD.
<p>
<b>Option keys:</b>
<ul>
<li>"dev" - Specifies audio device to use.
</ul>
<p>
<hr width="50%">
<h3>sun</h3>
Sun audio driver. This is the audio system for NetBSD, OpenBSD, and
Solaris.
<p>
<b>Option keys:</b>
<ul>
<li>"dev" - The audio device for the sound card. By default, the
driver tries "/dev/audio".
</ul>
<p>
<hr width="50%">
<h3>wmm</h3>
Windows MMSound output driver for Win98 and later.
<p>
<b>Option keys:</b>
<ul>
<li>"dev" - Selects audio device to use for playback by device name.
<li>"id" - Selects audio device to use for playback by device id (card number).
</ul>
<p>
<hr>
<h2>File Output Drivers</h2>
<h3>au</h3>
Sun audio file driver. Writes a .au file from audio output. This
driver can write usable data to unseekable files (like standard out),
which the wav driver cannot do.
<p>
<hr width="50%">
<h3>raw</h3>
Raw sample driver. Writes the sound to disk in uncompressed,
headerless form using the byte order specified.
<p>
<b>Option keys:</b>
<ul>
<li>"byteorder" - Byte order used in the output. Use "native" for
native machine byte order, "big" for big-endian order, and "little"
for little-endian order. By default this is "native".
</ul>
<p>
<hr width="50%">
<h3>wav</h3>
Windows 'WAV' sound file output. Because of the way WAV files are
structured, this driver cannot correct files unless the target file is
seekable. Writing WAVs to stdout will result in broken files. Use
either the raw or the au driver instead.
<p>
<hr>
<a name="default_driver">
<h2>Default Driver Detection</h2>
In the absence of <a href="config.html">configuration files</a> to
explicit identify a default driver, the library will try to detect a
suitable default driver. It does this by testing every available live
output driver (using <a
href="ao_plugin_test.html">ao_plugin_test()</a>) and finding the
driver with the highest priority (see the <a
href="ao_info.html">ao_info</a> struct) that works. Drivers with
priority 0, such as the null and file output drivers, are never
selected as the default.
<p>
The ranking system currently used is:
<center>
<table border="1">
<tr><th>Priority</th><th>Drivers</th> </tr>
<tr><td>50</td> <td>pulse, roar</td> </tr>
<tr><td>45</td> <td>arts*</td> </tr>
<tr><td>40</td> <td>esd</td> </tr>
<tr><td>35</td> <td>alsa</td> </tr>
<tr><td>30</td> <td>macosx, sndio </td> </tr>
<tr><td>20</td> <td>aixs, oss, irix, sun, wmm</td> </tr>
<tr><td>15</td> <td>arts*</td> </tr>
<tr><td>10</td> <td>nas</td> </tr>
<tr bgcolor="#888888"><td> 0</td> <td>null, all file output</td></tr>
</table>
</center>
<p>
<i>*arts priority depends on whether or not the arts install was built
with <tt>HAVE_ARTS_SUSPENDED</tt>; when present, the default aRts
priority is 45, else it is 15.</i>
<p>Clearly, any ranking scheme will fail to make everybody happy. For
such cases, the <a href="config.html">configuration files</a> can be
easily used to define an appropriate default output device.
<p>Adding <tt>debug</tt> to the libao <a
href="config.html">configuration file</a> on a line by itself will
cause libao to print what static and dynamic drivers are available for
use, as well as print the testing order.
<br><br>
<hr noshade>
<table border=0 width=100%>
<tr valign=top>
<td><p class=tiny>copyright © 2001-2003 Stan Seibert, 2010 Monty</p></td>
<td align=right><p class=tiny><a href="http://www.xiph.org/">xiph.org</a><br><a href="mailto:monty@xiph.org">monty@xiph.org</a></p></td>
</tr><tr>
<td><p class=tiny>libao documentation</p></td>
<td align=right><p class=tiny>libao version 1.0.0 - 20100325</p></td>
</tr>
</table>
</body>
</html>
|
