1page.title=Configuring Audio Policies 2@jd:body 3 4<!-- 5 Copyright 2016 The Android Open Source Project 6 7 Licensed under the Apache License, Version 2.0 (the "License"); 8 you may not use this file except in compliance with the License. 9 You may obtain a copy of the License at 10 11 http://www.apache.org/licenses/LICENSE-2.0 12 13 Unless required by applicable law or agreed to in writing, software 14 distributed under the License is distributed on an "AS IS" BASIS, 15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 See the License for the specific language governing permissions and 17 limitations under the License. 18--> 19<div id="qv-wrapper"> 20 <div id="qv"> 21 <h2>In this document</h2> 22 <ol id="auto-toc"> 23 </ol> 24 </div> 25</div> 26 27<p>Android 7.0 introduces a new audio policy configuration file format (XML) for 28describing your audio topology.</p> 29 30<p>Previous Android releases required using the 31<code>device/<company>/<device>/audio/audio_policy.conf</code> 32to declare the audio devices present on your product (you can see an example of 33this file for the Galaxy Nexus audio hardware in 34<code>device/samsung/tuna/audio/audio_policy.conf</code>). However, .conf is a 35simple proprietary format that is too limited to describe complex topologies for 36applications such as televisions and automobiles.</p> 37 38<p>Android 7.0 deprecates the <code>audio_policy.conf</code> and adds support 39for defining audio topology using an XML file format that is more 40human-readable, has a wide range of editing and parsing tools, and is flexible 41enough to describe complex audio topologies.</p> 42 43<p class="note".<strong>Note:</strong> Android 7.0 preserves support for using 44<code>audio_policy.conf</code>; this legacy format is used by default. To use 45the XML file format, include the build option <code>USE_XML_AUDIO_POLICY_CONF 46:= 1</code> in device makefile.</p> 47 48<h2 id=xml_advantages>Advantages of the XML format</h2> 49<p>As in the .conf file, the new XML file enables defining the number and types 50of output an input stream profiles, devices usable for playback and capture, and 51audio attributes. In addition, the XML format offers the following enhancements: 52</p> 53 54<ul> 55<li>Audio profiles are now structured similar to HDMI Simple Audio Descriptors 56and enable a different set of sampling rates/channel masks for each audio 57format.</li> 58<li>Explicit definitions of all possible connections between devices and 59streams. Previously, an implicit rule made it possible to interconnect all 60devices attached to the same HAL module, preventing the audio policy from 61controlling connections requested with audio patch APIs. In the XML format, the 62topology description now defines connection limitations.</li> 63<li>Support for <em>includes</em> avoids repeating standard A2DP, USB, or 64reroute submit definitions.</li> 65<li>Customizable volume curves. Previously, volume tables were hardcoded. In the 66XML format, volume tables are described and can be customized.</li> 67</ul> 68 69<p>The template at 70<code>frameworks/av/services/audiopolicy/config/audio_policy_configuration.xml</code> 71shows many of these features in use.</p> 72 73<h2 id=xml_file_format>File format and location</h2> 74<p>The new audio policy configuration file is 75<code>audio_policy_configuration.xml</code> and is located in 76<code>/system/etc</code>. To view a simple audio policy configuration in the new 77XML file format, view the example below.</p> 78 79<p> 80<div class="toggle-content closed"> 81 <p><a href="#" onclick="return toggleContent(this)"> 82 <img src="{@docRoot}assets/images/triangle-closed.png" class="toggle-content-img" /> 83 <strong><span class="toggle-content-text">Show audio policy example</span> 84 <span class="toggle-content-text" style="display:none;">Hide audio policy 85 example</span></strong> 86 </a></p> 87 88 <div class="toggle-content-toggleme"> 89<pre class="prettyprint"> 90<?xml version="1.0" encoding="UTF-8" standalone="yes"?> 91<audioPolicyConfiguration version="1.0" xmlns:xi="http://www.w3.org/2001/XInclude"> 92 <globalConfiguration speaker_drc_enabled="true"/> 93 <modules> 94 <module name="primary" halVersion="3.0"> 95 <attachedDevices> 96 <item>Speaker</item> 97 <item>Earpiece</item> 98 <item>Built-In Mic</item> 99 </attachedDevices> 100 <defaultOutputDevice>Speaker</defaultOutputDevice> 101 <mixPorts> 102 <mixPort name="primary output" role="source" flags="AUDIO_OUTPUT_FLAG_PRIMARY"> 103 <profile name="" format="AUDIO_FORMAT_PCM_16_BIT" 104 samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/> 105 </mixPort> 106 <mixPort name="primary input" role="sink"> 107 <profile name="" format="AUDIO_FORMAT_PCM_16_BIT" 108 samplingRates="8000,16000,48000" 109 channelMasks="AUDIO_CHANNEL_IN_MONO"/> 110 </mixPort> 111 </mixPorts> 112 <devicePorts> 113 <devicePort tagName="Earpiece" type="AUDIO_DEVICE_OUT_EARPIECE" role="sink"> 114 <profile name="" format="AUDIO_FORMAT_PCM_16_BIT" 115 samplingRates="48000" channelMasks="AUDIO_CHANNEL_IN_MONO"/> 116 </devicePort> 117 <devicePort tagName="Speaker" role="sink" type="AUDIO_DEVICE_OUT_SPEAKER" address=""> 118 <profile name="" format="AUDIO_FORMAT_PCM_16_BIT" 119 samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/> 120 </devicePort> 121 <devicePort tagName="Wired Headset" type="AUDIO_DEVICE_OUT_WIRED_HEADSET" role="sink"> 122 <profile name="" format="AUDIO_FORMAT_PCM_16_BIT" 123 samplingRates="48000" channelMasks="AUDIO_CHANNEL_OUT_STEREO"/> 124 </devicePort> 125 <devicePort tagName="Built-In Mic" type="AUDIO_DEVICE_IN_BUILTIN_MIC" role="source"> 126 <profile name="" format="AUDIO_FORMAT_PCM_16_BIT" 127 samplingRates="8000,16000,48000" 128 channelMasks="AUDIO_CHANNEL_IN_MONO"/> 129 </devicePort> 130 <devicePort tagName="Wired Headset Mic" type="AUDIO_DEVICE_IN_WIRED_HEADSET" role="source"> 131 <profile name="" format="AUDIO_FORMAT_PCM_16_BIT" 132 samplingRates="8000,16000,48000" 133 channelMasks="AUDIO_CHANNEL_IN_MONO"/> 134 </devicePort> 135 </devicePorts> 136 <routes> 137 <route type="mix" sink="Earpiece" sources="primary output"/> 138 <route type="mix" sink="Speaker" sources="primary output"/> 139 <route type="mix" sink="Wired Headset" sources="primary output"/> 140 <route type="mix" sink="primary input" sources="Built-In Mic,Wired Headset Mic"/> 141 </routes> 142 </module> 143 <xi:include href="a2dp_audio_policy_configuration.xml"/> 144 </modules> 145 146 <xi:include href="audio_policy_volumes.xml"/> 147 <xi:include href="default_volume_tables.xml"/> 148</audioPolicyConfiguration> 149</pre></div></div> 150</p> 151 152<p>The top level structure contains modules that correspond to each audio HAL 153hardware module, where each module has a list of mix ports, device ports, and 154routes:</p> 155<ul> 156<li><strong>Mix ports</strong> describe the possible config profiles for streams 157that can be opened at the audio HAL for playback and capture.</li> 158<li><strong>Device ports</strong> describe the devices that can be attached with 159their type (and optionally address and audio properties, if relevant).</li> 160<li><strong>Routes</strong> (new) is now separated from the mix port descriptor, 161enabling description of routes from device to device or stream to device.</li> 162</ul> 163 164<p>Volume tables are simple lists of points defining the curve used to translate 165form a UI index to a volume in dB. A separate include file provides default 166curves, but each curve for a given use case and device category can be 167overwritten.</p> 168 169<div class="toggle-content closed"> 170 <p><a href="#" onclick="return toggleContent(this)"> 171 <img src="{@docRoot}assets/images/triangle-closed.png" class="toggle-content-img" /> 172 <strong><span class="toggle-content-text">Show volume table example</span> 173 <span class="toggle-content-text" style="display:none;">Hide volume table 174 example</span></strong> 175 </a></p> 176 177 <div class="toggle-content-toggleme"> 178<p><pre> 179<?xml version="1.0" encoding="UTF-8"?> 180<volumes> 181 <reference name="FULL_SCALE_VOLUME_CURVE"> 182 <point>0,0</point> 183 <point>100,0</point> 184 </reference> 185 <reference name="SILENT_VOLUME_CURVE"> 186 <point>0,-9600</point> 187 <point>100,-9600</point> 188 </reference> 189 <reference name="DEFAULT_VOLUME_CURVE"> 190 <point>1,-4950</point> 191 <point>33,-3350</point> 192 <point>66,-1700</point> 193 <point>100,0</point> 194 </reference> 195</volumes> 196</pre></p></div></div> 197 198<div class="toggle-content closed"> 199 <p><a href="#" onclick="return toggleContent(this)"> 200 <img src="{@docRoot}assets/images/triangle-closed.png" class="toggle-content-img" /> 201 <strong><span class="toggle-content-text">Show volumes example</span> 202 <span class="toggle-content-text" style="display:none;">Hide volumes 203 example</span></strong> 204 </a></p> 205 206 <div class="toggle-content-toggleme"> 207<p><pre> 208<?xml version="1.0" encoding="UTF-8"?> 209<volumes> 210 <volume stream="AUDIO_STREAM_VOICE_CALL" deviceCategory="DEVICE_CATEGORY_HEADSET" ref="DEFAULT_VOLUME_CURVE"/> 211 <volume stream="AUDIO_STREAM_VOICE_CALL" deviceCategory="DEVICE_CATEGORY_SPEAKER" ref="DEFAULT_VOLUME_CURVE"/> 212 <volume stream="AUDIO_STREAM_VOICE_CALL" deviceCategory="DEVICE_CATEGORY_EARPIECE" ref="DEFAULT_VOLUME_CURVE"/> 213 <volume stream="AUDIO_STREAM_VOICE_CALL" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA" ref="DEFAULT_VOLUME_CURVE"/> 214 215 <volume stream="AUDIO_STREAM_SYSTEM" deviceCategory="DEVICE_CATEGORY_HEADSET" ref="DEFAULT_VOLUME_CURVE"/> 216 <volume stream="AUDIO_STREAM_SYSTEM" deviceCategory="DEVICE_CATEGORY_SPEAKER" ref="DEFAULT_VOLUME_CURVE"/> 217 <volume stream="AUDIO_STREAM_SYSTEM" deviceCategory="DEVICE_CATEGORY_EARPIECE" ref="DEFAULT_VOLUME_CURVE"/> 218 <volume stream="AUDIO_STREAM_SYSTEM" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA" ref="DEFAULT_VOLUME_CURVE"/> 219 220 <volume stream="AUDIO_STREAM_RING" deviceCategory="DEVICE_CATEGORY_HEADSET" ref="DEFAULT_VOLUME_CURVE"/> 221 <volume stream="AUDIO_STREAM_RING" deviceCategory="DEVICE_CATEGORY_SPEAKER" ref="DEFAULT_VOLUME_CURVE"/> 222 <volume stream="AUDIO_STREAM_RING" deviceCategory="DEVICE_CATEGORY_EARPIECE" ref="DEFAULT_VOLUME_CURVE"/> 223 <volume stream="AUDIO_STREAM_RING" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA"ref="DEFAULT_VOLUME_CURVE"/> 224 225 <volume stream="AUDIO_STREAM_MUSIC" deviceCategory="DEVICE_CATEGORY_HEADSET" ref="DEFAULT_VOLUME_CURVE"/> 226 <volume stream="AUDIO_STREAM_MUSIC" deviceCategory="DEVICE_CATEGORY_SPEAKER"> 227 <point>1,-5500</point> 228 <point>20,-4300</point> 229 <point>86,-1200</point> 230 <point>100,0</point> 231 </volume> 232 <volume stream="AUDIO_STREAM_MUSIC" deviceCategory="DEVICE_CATEGORY_EARPIECE" ref="DEFAULT_VOLUME_CURVE"/> 233 <volume stream="AUDIO_STREAM_MUSIC" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA" ref="DEFAULT_VOLUME_CURVE"/> 234 235 <volume stream="AUDIO_STREAM_ALARM" deviceCategory="DEVICE_CATEGORY_HEADSET" ref="DEFAULT_VOLUME_CURVE"/> 236 <volume stream="AUDIO_STREAM_ALARM" deviceCategory="DEVICE_CATEGORY_SPEAKER" ref="DEFAULT_VOLUME_CURVE"/> 237 <volume stream="AUDIO_STREAM_ALARM" deviceCategory="DEVICE_CATEGORY_EARPIECE" ref="DEFAULT_VOLUME_CURVE"/> 238 <volume stream="AUDIO_STREAM_ALARM" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA" ref="DEFAULT_VOLUME_CURVE"/> 239 240 <volume stream="AUDIO_STREAM_NOTIFICATION" deviceCategory="DEVICE_CATEGORY_HEADSET" ref="DEFAULT_VOLUME_CURVE"/> 241 <volume stream="AUDIO_STREAM_NOTIFICATION" deviceCategory="DEVICE_CATEGORY_SPEAKER" ref="DEFAULT_VOLUME_CURVE"/> 242 <volume stream="AUDIO_STREAM_NOTIFICATION" deviceCategory="DEVICE_CATEGORY_EARPIECE" ref="DEFAULT_VOLUME_CURVE"/> 243 <volume stream="AUDIO_STREAM_NOTIFICATION" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA" ref="DEFAULT_VOLUME_CURVE"/> 244 245 <volume stream="AUDIO_STREAM_BLUETOOTH_SCO" deviceCategory="DEVICE_CATEGORY_HEADSET" ref="DEFAULT_VOLUME_CURVE"/> 246 <volume stream="AUDIO_STREAM_BLUETOOTH_SCO" deviceCategory="DEVICE_CATEGORY_SPEAKER" ref="DEFAULT_VOLUME_CURVE"/> 247 <volume stream="AUDIO_STREAM_BLUETOOTH_SCO" deviceCategory="DEVICE_CATEGORY_EARPIECE" ref="DEFAULT_VOLUME_CURVE"/> 248 <volume stream="AUDIO_STREAM_BLUETOOTH_SCO" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA" ref="DEFAULT_VOLUME_CURVE"/> 249 250 <volume stream="AUDIO_STREAM_ENFORCED_AUDIBLE" deviceCategory="DEVICE_CATEGORY_HEADSET" ref="DEFAULT_VOLUME_CURVE"/> 251 <volume stream="AUDIO_STREAM_ENFORCED_AUDIBLE" deviceCategory="DEVICE_CATEGORY_SPEAKER" ref="DEFAULT_VOLUME_CURVE"/> 252 <volume stream="AUDIO_STREAM_ENFORCED_AUDIBLE" deviceCategory="DEVICE_CATEGORY_EARPIECE" ref="DEFAULT_VOLUME_CURVE"/> 253 <volume stream="AUDIO_STREAM_ENFORCED_AUDIBLE" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA" ref="DEFAULT_VOLUME_CURVE"/> 254 255 <volume stream="AUDIO_STREAM_DTMF" deviceCategory="DEVICE_CATEGORY_SPEAKER" ref="DEFAULT_VOLUME_CURVE"/> 256 <volume stream="AUDIO_STREAM_DTMF" deviceCategory="DEVICE_CATEGORY_SPEAKER" ref="DEFAULT_VOLUME_CURVE"/> 257 <volume stream="AUDIO_STREAM_DTMF" deviceCategory="DEVICE_CATEGORY_EARPIECE" ref="DEFAULT_VOLUME_CURVE"/> 258 <volume stream="AUDIO_STREAM_DTMF" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA" ref="DEFAULT_VOLUME_CURVE"/> 259 260 <volume stream="AUDIO_STREAM_TTS" deviceCategory="DEVICE_CATEGORY_HEADSET" ref="SILENT_VOLUME_CURVE"/> 261 <volume stream="AUDIO_STREAM_TTS" deviceCategory="DEVICE_CATEGORY_SPEAKER" ref="FULL_SCALE_VOLUME_CURVE"/> 262 <volume stream="AUDIO_STREAM_TTS" deviceCategory="DEVICE_CATEGORY_EARPIECE" ref="SILENT_VOLUME_CURVE"/> 263 <volume stream="AUDIO_STREAM_TTS" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA" ref="SILENT_VOLUME_CURVE"/> 264 265 <volume stream="AUDIO_STREAM_ACCESSIBILITY" deviceCategory="DEVICE_CATEGORY_HEADSET" ref="DEFAULT_VOLUME_CURVE"/> 266 <volume stream="AUDIO_STREAM_ACCESSIBILITY" deviceCategory="DEVICE_CATEGORY_SPEAKER" ref="DEFAULT_VOLUME_CURVE"/> 267 <volume stream="AUDIO_STREAM_ACCESSIBILITY" deviceCategory="DEVICE_CATEGORY_EARPIECE" ref="DEFAULT_VOLUME_CURVE"/> 268 <volume stream="AUDIO_STREAM_ACCESSIBILITY" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA" ref="DEFAULT_VOLUME_CURVE"/> 269 270 <volume stream="AUDIO_STREAM_REROUTING" deviceCategory="DEVICE_CATEGORY_HEADSET" ref="FULL_SCALE_VOLUME_CURVE"/> 271 <volume stream="AUDIO_STREAM_REROUTING" deviceCategory="DEVICE_CATEGORY_SPEAKER" ref="FULL_SCALE_VOLUME_CURVE"/> 272 <volume stream="AUDIO_STREAM_REROUTING" deviceCategory="DEVICE_CATEGORY_EARPIECE" ref="FULL_SCALE_VOLUME_CURVE"/> 273 <volume stream="AUDIO_STREAM_REROUTING" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA" ref="FULL_SCALE_VOLUME_CURVE"/> 274 275 <volume stream="AUDIO_STREAM_PATCH" deviceCategory="DEVICE_CATEGORY_HEADSET" ref="FULL_SCALE_VOLUME_CURVE"/> 276 <volume stream="AUDIO_STREAM_PATCH" deviceCategory="DEVICE_CATEGORY_SPEAKER" ref="FULL_SCALE_VOLUME_CURVE"/> 277 <volume stream="AUDIO_STREAM_PATCH" deviceCategory="DEVICE_CATEGORY_EARPIECE" ref="FULL_SCALE_VOLUME_CURVE"/> 278 <volume stream="AUDIO_STREAM_PATCH" deviceCategory="DEVICE_CATEGORY_EXT_MEDIA" ref="FULL_SCALE_VOLUME_CURVE"/> 279</volumes> 280</pre></p></div></div> 281 282<h2 id=file_inclusions>File inclusions</h2> 283<p>The XML Inclusions (XInclude) method can be used to include audio policy 284configuration information located in other XML files. All included files must 285follow the structure described above with the following restrictions:</p> 286<ul> 287<li>Files can contain only top-level elements.</li> 288<li>Files cannot contain Xinclude elements.</li> 289</ul> 290<p>Use includes to avoid copying standard Android Open Source Project (AOSP) 291audio HAL modules configuration information to all audio policy configuration 292files (which is prone to errors). A standard audio policy configuration xml file 293is provided for the following audio HALs:</p> 294<ul> 295<li><strong>A2DP:</strong> <code>a2dp_audio_policy_configuration.xml</code></li> 296<li><strong>Reroute submix:</strong> <code>rsubmix_audio_policy_configuration.xml</code></li> 297<li><strong>USB:</strong> <code>usb_audio_policy_configuration.xml</code></li> 298</ul> 299 300<h2 id=code_reorg>Audio policy code reorganization</h2> 301<p>Android 7.0 splits <code>AudioPolicyManager.cpp</code> into several modules 302to make it more maintainable and to highlight what is configurable. The new 303organization of <code>frameworks/av/services/audiopolicy</code> includes the 304following modules:</p> 305 306<table> 307<tr> 308<th>Module</th> 309<th>Description</th> 310</tr> 311 312<tr> 313<td><code>/managerdefault</code></td> 314<td>Includes the generic interfaces and behavior implementation common to all 315applications. Similar to <code>AudioPolicyManager.cpp</code> with engine 316functionality and common concepts abstracted away.</td> 317</tr> 318 319<tr> 320<td><code>/common</code></td> 321<td>Defines base classes (e.g data structures for input output audio stream 322profiles, audio device descriptors, audio patches, audio port, etc.). Previously 323defined inside <code>AudioPolicyManager.cpp</code>.</td> 324</tr> 325 326<tr> 327<td><code>/engine</code></td> 328<td><p>Implements the rules that define which device and volumes should be used for 329a given use case. It implements a standard interface with the generic part, such 330as to get the appropriate device for a given playback or capture use case, or to 331set connected devices or external state (i.e. a call state of forced usage) that 332can alter the routing decision.</p> 333<p>Available in two versions, customized and default; use build option 334<code>USE_CONFIGURABLE_AUDIO_POLICY</code> to select.</p></td> 335</tr> 336 337<tr> 338<td><code>/engineconfigurable</code></td> 339<td>Policy engine implementation that relies on parameter framework (see below). 340Configuration is based on the parameter framework and where the policy is 341defined by XML files.</td> 342</tr> 343 344<tr> 345<td><code>/enginedefault</code></td> 346<td>Policy engine implementation based on previous Android Audio Policy Manager 347implementations. This is the default and includes hard coded rules that 348correspond to current Nexus and AOSP implementations.</td> 349</tr> 350 351<tr> 352<td><code>/service</code></td> 353<td>Includes binder interfaces, threading and locking implementation with 354interface to the rest of the framework.</td> 355</tr> 356 357</table> 358 359<h2 id=policy_config>Configuration using parameter-framework</h2> 360<p>Android 7.0 reorganizes audio policy code to make it easier to understand and 361maintain while also supporting an audio policy defined entirely by configuration 362files. The reorganization and audio policy design is based on Intel's parameter 363framework, a plugin-based and rule-based framework for handling parameters.</p> 364 365<p>Using the new configurable audio policy enables vendors OEMs to:</p> 366<ul> 367<li>Describe a system's structure and its parameters in XML.</li> 368<li>Write (in C++) or reuse a backend (plugin) for accessing described 369parameters.</li> 370<li>Define (in XML or in a domain-specific language) conditions/rules upon which 371a given parameter must take a given value.</li> 372</ul> 373 374<p>AOSP includes an example of an audio policy configuration file that uses the parameter-framework at: <code>Frameworks/av/services/audiopolicy/engineconfigurable/parameter-framework/example/Settings/PolicyConfigurableDomains.xml</code>. For 375details, refer to Intel documentation on the 376<a href="https://github.com/01org/parameter-framework">parameter-framework</a> 377and 378<a href="http://01org.github.io/parameter-framework/hosting/Android_M_Configurable_Audio_Policy.pdf">Android 379Configurable Audio Policy</a>.</p> 380 381<h2 id=policy_routing_apis>Audio policy routing APIs</h2> 382<p>Android 6.0 introduced a public Enumeration and Selection API that sits on 383top of the audio patch/audio port infrastructure and allows application 384developers to indicate a preference for a specific device output or input for 385connected audio records or tracks.</p> 386<p>In Android 7.0, the Enumeration and Selection API is verified by CTS tests 387and is extended to include routing for native C/C++ (OpenSL ES) audio streams. 388The routing of native streams continues to be done in Java, with the addition of 389an <code>AudioRouting</code> interface that supersedes, combines, and deprecates 390the explicit routing methods that were specific to <code>AudioTrack</code> and 391<code>AudioRecord</code> classes.</p> 392 393<p>For details on the Enumeration and Selection API, refer to 394<a href="https://developer.android.com/ndk/guides/audio/opensl-for-android.html?hl=fi#configuration-interface">Android 395configuration interfaces</a> and <code>OpenSLES_AndroidConfiguration.h</code>. 396For details on audio routing, refer to 397<a href="https://developer.android.com/reference/android/media/AudioRouting.html">AudioRouting</a>. 398</p> 399 400<h2 id=multichannel>Multi-channel support</h2> 401 402<p>If your hardware and driver supports multichannel audio via HDMI, you can 403output the audio stream directly to the audio hardware (this bypasses the 404AudioFlinger mixer so it doesn't get downmixed to two channels.) The audio HAL 405must expose whether an output stream profile supports multichannel audio 406capabilities. If the HAL exposes its capabilities, the default policy manager 407allows multichannel playback over HDMI. For implementation details, see 408<code>device/samsung/tuna/audio/audio_hw.c</code>.</p> 409 410<p>To specify that your product contains a multichannel audio output, edit the 411audio policy configuration file to describe the multichannel output for your 412product. The following example from a Galaxy Nexus shows a <em>dynamic</em> 413channel mask, which means the audio policy manager queries the actual channel 414masks supported by the HDMI sink after connection.</p> 415 416<pre> 417audio_hw_modules { 418 primary { 419 outputs { 420 ... 421 hdmi { 422 sampling_rates 44100|48000 423 channel_masks dynamic 424 formats AUDIO_FORMAT_PCM_16_BIT 425 devices AUDIO_DEVICE_OUT_AUX_DIGITAL 426 flags AUDIO_OUTPUT_FLAG_DIRECT 427 } 428 ... 429 } 430 ... 431 } 432 ... 433} 434</pre> 435 436<p>You can also specify a static channel mask such as 437<code>AUDIO_CHANNEL_OUT_5POINT1</code>. AudioFlinger's mixer downmixes the 438content to stereo automatically when sent to an audio device that does not 439support multichannel audio.</p> 440 441<h2 id=codecs>Media codecs</h2> 442 443<p>Ensure the audio codecs your hardware and drivers support are properly 444declared for your product. For details, see 445<a href="{@docRoot}devices/media/index.html#expose">Exposing Codecs to the 446Framework</a>.</p> 447
