en/devices/audio/latency_app.html - platform/docs/source.android.com - Git at Google

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     <title>Audio Latency for App Developers</title>
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 <p>For the lowest audio latency possible, we recommend you use Android native audio
 based on OpenSL ES 1.0.1.</p>

 <h2 id="implementation">Implementation checklist</h2>

 <p>To use Android native audio:</p>

 <ol>

 <li>
 Download and install the
 <a href="https://developer.android.com/tools/sdk/ndk/index.html">Android NDK</a>.
 In the rest of this document, we'll assume <code>NDKroot</code> is the
 directory where you installed NDK.
 </li>

 <li>
 Read the <a href="#supporting">supporting documentation.</a>
 </li>

 <li>
 Check for API level 9 or higher.
 </li>

 <li>
 Check for feature
 <a href="http://developer.android.com/guide/topics/manifest/uses-feature-element.html#hw-features">android.hardware.audio.low_latency.</a>
 </li>

 <li>
 Use the recommended native buffer size and sample rate returned by
 <a href="http://developer.android.com/reference/android/media/AudioManager.html#getProperty(java.lang.String)">android.media.AudioManager.getProperty(java.lang.String)</a>
 <p> <strong>Note</strong>: the same buffer size and sample rate should also be used for input.</p>
 </li>

 <li>
 Usually an OpenSL ES buffer count of 1 is sufficient.
 </li>

 <li>
 Keep your callback handlers short, without bursty CPU usage or unbounded blocking.  Avoid
 <a href="avoiding_pi.html">priority inversion.</a>
 </li>

 <li>
 Consider using
 <a href="avoiding_pi.html#nonBlockingAlgorithms">non-blocking algorithms</a>
 to communicate between input and output callback handlers,
 and between the callback handlers and the rest of your application.
 </li>

 </ol>

 <h2 id="supporting">Supporting documentation</h2>

 <h3 id="opensl_es_1_0_1">OpenSL ES 1.0.1</h3>

 <p>
 Use a PDF viewer to review the
 <a href="https://www.khronos.org/registry/sles/specs/OpenSL_ES_Specification_1.0.1.pdf">OpenSL 1.0.1 Specification.</a>
 This is a rather long reference, and not all of it will be relevant to you; but you
 will need to consult it for details on the API.
 </p>

 <p class="note">
 <strong>Note</strong>: this document describes the full OpenSL ES 1.0.1, but Android
 native audio is actually based on a subset of OpenSL ES 1.0.1 with some Android-specific extensions.
 </p>

 <p>
 Documents describing later versions of OpenSL ES, such as 1.1,
 are not relevant to Android.
 </p>

 <h3 id="opensl_es_for_android">OpenSL ES for Android</h3>

 <p>
 The document "OpenSL ES for Android" is provided in the NDK installation,
 and is not currently available online.  Open this link in a browser:
 </p>

 <pre class="devsite-click-to-copy">
 NDKroot/docs/Additional_library_docs/opensles/index.html
 </pre>

 <p>
 You'll want to skim the whole
 document, but pay special attention to the "Performance" subsection of the
 "Programming notes" section.
 </p>

 <p>
 Section "Supported features from OpenSL ES 1.0.1"
 describes the subset supported by Android.
 </p>

 <p>
 Section "Android extensions" describes Android-specific extensions
 that aren't included in base OpenSL ES 1.0.1.
 </p>

 <h3 id="relationship">Relationship with OpenSL ES 1.0.1</h3>

 <p>
 This Venn diagram shows the relationship between
 Android native audio and OpenSL ES 1.0.1.
 </p>

 <img src="images/venn.png" alt="Venn diagram" id="figure1" />
 <p class="img-caption">
   <strong>Figure 1.</strong> Venn diagram
 </p>

 <h2 id="resources">Other resources</h2>

 <h3 id="source_android_com">source.android.com</h3>

 <p>
 The site <a href="/">source.android.com</a>
 is primarily designed for OEMs building Android
 devices, and the SoC vendors who supply components to these OEMs.
 </p>

 <p>
 However, there is a wealth of useful information about latency at this site, so
 you may want to review it.  See the articles at
 <a href="latency.html">Audio Latency.</a>
 </p>

 <h3 id="android_ndk">android-ndk</h3>

 <p>
 If you have questions about how to use Android native audio, you can ask at the discussion group
 <a href="https://groups.google.com/forum/#!forum/android-ndk">android-ndk.</a>
 </p>

 <h3 id="videos">Videos</h3>

 <dl>

 <dt><a href="https://youtu.be/d3kfEeMZ65c">High performance audio on Android</a>
 (Google I/O 2013)</dt>
 <dd>The whole video is about latency.</dd>

 <dt><a href="https://youtu.be/92fgcUNCHic">Building great multi-media experiences on Android</a>
 (Google I/O 2014)</dt>
 <dd>The first 14 minutes are about audio in general and input latency in particular.</dd>

 <dt><a href="https://youtu.be/PnDK17zP9BI">Audio latency: buffer sizes</a>
 (100 Days of Google Dev)</dt>
 <dd>Describes the relationship between audio latency, buffer sizes, and task scheduling.</dd>

 </dl>

   </body>
 </html>
	<html devsite>
	<head>
	<title>Audio Latency for App Developers</title>
	<meta name="project_path" value="/_project.yaml" />
	<meta name="book_path" value="/_book.yaml" />
	</head>
	<body>
	<!--
	Copyright 2017 The Android Open Source Project

	Licensed under the Apache License, Version 2.0 (the "License");
	you may not use this file except in compliance with the License.
	You may obtain a copy of the License at

	http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software
	distributed under the License is distributed on an "AS IS" BASIS,
	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	See the License for the specific language governing permissions and
	limitations under the License.
	-->



	<p>For the lowest audio latency possible, we recommend you use Android native audio
	based on OpenSL ES 1.0.1.</p>

	<h2 id="implementation">Implementation checklist</h2>

	<p>To use Android native audio:</p>

	<ol>

	<li>
	Download and install the
	<a href="https://developer.android.com/tools/sdk/ndk/index.html">Android NDK</a>.
	In the rest of this document, we'll assume <code>NDKroot</code> is the
	directory where you installed NDK.
	</li>

	<li>
	Read the <a href="#supporting">supporting documentation.</a>
	</li>

	<li>
	Check for API level 9 or higher.
	</li>

	<li>
	Check for feature
	<a href="http://developer.android.com/guide/topics/manifest/uses-feature-element.html#hw-features">android.hardware.audio.low_latency.</a>
	</li>

	<li>
	Use the recommended native buffer size and sample rate returned by
	<a href="http://developer.android.com/reference/android/media/AudioManager.html#getProperty(java.lang.String)">android.media.AudioManager.getProperty(java.lang.String)</a>
	<p> <strong>Note</strong>: the same buffer size and sample rate should also be used for input.</p>
	</li>

	<li>
	Usually an OpenSL ES buffer count of 1 is sufficient.
	</li>

	<li>
	Keep your callback handlers short, without bursty CPU usage or unbounded blocking. Avoid
	<a href="avoiding_pi.html">priority inversion.</a>
	</li>

	<li>
	Consider using
	<a href="avoiding_pi.html#nonBlockingAlgorithms">non-blocking algorithms</a>
	to communicate between input and output callback handlers,
	and between the callback handlers and the rest of your application.
	</li>

	</ol>

	<h2 id="supporting">Supporting documentation</h2>

	<h3 id="opensl_es_1_0_1">OpenSL ES 1.0.1</h3>

	<p>
	Use a PDF viewer to review the
	<a href="https://www.khronos.org/registry/sles/specs/OpenSL_ES_Specification_1.0.1.pdf">OpenSL 1.0.1 Specification.</a>
	This is a rather long reference, and not all of it will be relevant to you; but you
	will need to consult it for details on the API.
	</p>

	<p class="note">
	<strong>Note</strong>: this document describes the full OpenSL ES 1.0.1, but Android
	native audio is actually based on a subset of OpenSL ES 1.0.1 with some Android-specific extensions.
	</p>

	<p>
	Documents describing later versions of OpenSL ES, such as 1.1,
	are not relevant to Android.
	</p>

	<h3 id="opensl_es_for_android">OpenSL ES for Android</h3>

	<p>
	The document "OpenSL ES for Android" is provided in the NDK installation,
	and is not currently available online. Open this link in a browser:
	</p>

	<pre class="devsite-click-to-copy">
	NDKroot/docs/Additional_library_docs/opensles/index.html
	</pre>

	<p>
	You'll want to skim the whole
	document, but pay special attention to the "Performance" subsection of the
	"Programming notes" section.
	</p>

	<p>
	Section "Supported features from OpenSL ES 1.0.1"
	describes the subset supported by Android.
	</p>

	<p>
	Section "Android extensions" describes Android-specific extensions
	that aren't included in base OpenSL ES 1.0.1.
	</p>

	<h3 id="relationship">Relationship with OpenSL ES 1.0.1</h3>

	<p>
	This Venn diagram shows the relationship between
	Android native audio and OpenSL ES 1.0.1.
	</p>

	<img src="images/venn.png" alt="Venn diagram" id="figure1" />
	<p class="img-caption">
	<strong>Figure 1.</strong> Venn diagram
	</p>

	<h2 id="resources">Other resources</h2>

	<h3 id="source_android_com">source.android.com</h3>

	<p>
	The site <a href="/">source.android.com</a>
	is primarily designed for OEMs building Android
	devices, and the SoC vendors who supply components to these OEMs.
	</p>

	<p>
	However, there is a wealth of useful information about latency at this site, so
	you may want to review it. See the articles at
	<a href="latency.html">Audio Latency.</a>
	</p>

	<h3 id="android_ndk">android-ndk</h3>

	<p>
	If you have questions about how to use Android native audio, you can ask at the discussion group
	<a href="https://groups.google.com/forum/#!forum/android-ndk">android-ndk.</a>
	</p>

	<h3 id="videos">Videos</h3>

	<dl>

	<dt><a href="https://youtu.be/d3kfEeMZ65c">High performance audio on Android</a>
	(Google I/O 2013)</dt>
	<dd>The whole video is about latency.</dd>

	<dt><a href="https://youtu.be/92fgcUNCHic">Building great multi-media experiences on Android</a>
	(Google I/O 2014)</dt>
	<dd>The first 14 minutes are about audio in general and input latency in particular.</dd>

	<dt><a href="https://youtu.be/PnDK17zP9BI">Audio latency: buffer sizes</a>
	(100 Days of Google Dev)</dt>
	<dd>Describes the relationship between audio latency, buffer sizes, and task scheduling.</dd>

	</dl>

	</body>
	</html>