1page.title=Audio Implementation
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19<div id="qv-wrapper">
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21    <h2>In this document</h2>
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23    </ol>
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26
27<p>This section explains how to implement the audio Hardware Abstraction Layer
28(HAL), provides details about configuring an audio policy (file formats, code
29organization, pre-processing effects), and describes how to configure the shared
30library (creating the <code>Android.mk</code> file).</p>
31
32<h2 id=implementing>Implementing the audio HAL</h2>
33
34<p>The audio HAL is composed of the following interfaces:</p>
35
36<ul>
37<li><code>hardware/libhardware/include/hardware/audio.h</code>. Represents the
38main functions of an audio device.</li>
39<li><code>hardware/libhardware/include/hardware/audio_effect.h</code>.
40Represents effects that can be applied to audio such as downmixing, echo, or
41noise suppression.</li>
42</ul>
43
44<p>You must implement all interfaces.</p>
45
46<h2 id=headers>Audio header files</h2>
47<p>For a reference of the properties you can define, refer to the audio header
48files:</p>
49
50<ul>
51<li>In Android 6.0 and higher, see
52<code>system/media/audio/include/system/audio.h</code>.</li>
53<li>In Android 5.1 and lower, see
54<code>system/core/include/system/audio.h</code>.</li>
55</ul>
56
57<p>For an example, refer to the implementation for the Galaxy Nexus at
58<code>device/samsung/tuna/audio</code>.</p>
59
60<h2 id=next-steps>Next steps</h2>
61
62<p>In addition to implementing the audio HAL, you must also create an
63<a href="{@docRoot}devices/audio/implement-policy.html">audio policy
64configuration file</a> that describes your audio topology and package the HAL
65implementation into a
66<a href="{@docRoot}devices/audio/implement-shared-library.html">shared
67library</a>. You can also configure
68<a href="{@docRoot}devices/audio/implement-pre-processing.html">pre-processing
69effects</a> such as automatic gain control and noise suppression.</p>
70