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<html devsite>
<head>
<title>Audio Implementation</title>
<meta name="project_path" value="/_project.yaml" />
<meta name="book_path" value="/_book.yaml" />
</head>
<body>
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<p>This section explains how to implement the audio Hardware Abstraction Layer
(HAL), provides details about configuring an audio policy (file formats, code
organization, pre-processing effects), and describes how to configure the shared
library (creating the <code>Android.mk</code> file).</p>
<h2 id=implementing>Implementing the audio HAL</h2>
<p>The audio HAL is composed of the following interfaces:</p>
<ul>
<li><code>hardware/libhardware/include/hardware/audio.h</code>. Represents the
main functions of an audio device.</li>
<li><code>hardware/libhardware/include/hardware/audio_effect.h</code>.
Represents effects that can be applied to audio such as downmixing, echo, or
noise suppression.</li>
</ul>
<p>You must implement all interfaces.</p>
<h2 id=headers>Audio header files</h2>
<p>For a reference of the properties you can define, refer to the audio header
files:</p>
<ul>
<li>In Android 6.0 and higher, see
<code>system/media/audio/include/system/audio.h</code>.</li>
<li>In Android 5.1 and lower, see
<code>system/core/include/system/audio.h</code>.</li>
</ul>
<p>For an example, refer to the implementation for the Galaxy Nexus at
<code>device/samsung/tuna/audio</code>.</p>
<h2 id=next-steps>Next steps</h2>
<p>In addition to implementing the audio HAL, you must also create an
<a href="/devices/audio/implement-policy.html">audio policy
configuration file</a> that describes your audio topology and package the HAL
implementation into a
<a href="/devices/audio/implement-shared-library.html">shared
library</a>. You can also configure
<a href="/devices/audio/implement-pre-processing.html">pre-processing
effects</a> such as automatic gain control and noise suppression.</p>
</body>
</html>