src/devices/audio/index.jd

page.title=Audio
@jd:body

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<div id="qv-wrapper">
  <div id="qv">
    <h2>In this document</h2>
    <ol id="auto-toc">
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<img style="float: right; margin: 0px 15px 15px 15px;"
src="images/ape_fwk_hal_audio.png" alt="Android Audio HAL icon"/>

<p>
Android's audio Hardware Abstraction Layer (HAL) connects the higher-level,
audio-specific framework APIs in <a href="http://developer.android.com/reference/android/media/package-summary.html">android.media</a> to the underlying audio driver and
hardware. This section includes implementation instructions and tips for
improving performance.
</p>

<h2 id="Architecture">Audio Architecture</h2>
<p>
Android audio architecture defines how audio functionality is implemented and
points to the relevant source code involved in the implementation.
</p>

<img src="images/ape_fwk_audio.png" alt="Audio architecture" id="figure1" />

<p class="img-caption">
<strong>Figure 1.</strong> Android audio architecture
</p>

<dl>

<dt>
Application framework
</dt>
<dd>
The application framework includes the app code, which uses the <a href="http://developer.android.com/reference/android/media/package-summary.html">android.media</a> APIs to
interact with audio hardware. Internally, this code calls corresponding JNI glue
classes to access the native code that interacts with audio hardware.
</dd>

<dt>
JNI
</dt>
<dd>
The JNI code associated with <a href="http://developer.android.com/reference/android/media/package-summary.html">android.media</a> calls lower level native code to access audio
hardware. JNI is located in <code>frameworks/base/core/jni/</code> and
<code>frameworks/base/media/jni</code>.
</dd>

<dt>
Native framework
</dt>
<dd>
The native framework provides a native equivalent to the <a href="http://developer.android.com/reference/android/media/package-summary.html">android.media</a> package, calling
Binder IPC proxies to access the audio-specific services of the media server.
Native framework code is located in <code>frameworks/av/media/libmedia</code>.
</dd>

<dt>
Binder IPC
</dt>
<dd>
Binder IPC proxies facilitate communication over process boundaries. Proxies are
located in <code>frameworks/av/media/libmedia</code> and begin with the letter
"I".
</dd>

<dt>
Media server
</dt>
<dd>
The media server contains audio services, which are the actual code that
interacts with your HAL implementations. The media server is located in
<code>frameworks/av/services/audioflinger</code>.
</dd>

<dt>
HAL
</dt>
<dd>
The HAL defines the standard interface that audio services call into and that
you must implement for your audio hardware to function correctly. The audio HAL
interfaces are located in <code>hardware/libhardware/include/hardware</code>.
For details, see <a
href="{@docRoot}devices/halref/audio_8h_source.html">hardware/audio.h</a>.
</dd>

<dt>
Kernel driver
</dt>
<dd>
The audio driver interacts with your hardware and HAL implementation. You can
use Advanced Linux Sound Architecture (ALSA), Open Sound System (OSS), or a
custom driver (HAL is driver-agnostic).
<p class="note"><strong>Note</strong>: If you use ALSA, we recommend
<code>external/tinyalsa</code> for the user portion of the driver because of its
compatible licensing (the standard user-mode library is GPL-licensed).</p>
</dd>

<dt>
Android native audio based on Open SL ES <em>(not shown)</em>
</dt>
<dd>
This API is exposed as part of
<a href="https://developer.android.com/tools/sdk/ndk/index.html">Android NDK</a>
and is at the same architecture level as
<a href="http://developer.android.com/reference/android/media/package-summary.html">android.media</a>.
</dd>

</dl>