Clay Murphy | 47b1d3f | 2013-10-03 10:02:22 -0700 | [diff] [blame] | 1 | page.title=Audio |
| 2 | @jd:body |
| 3 | |
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Clay Murphy | 768b82a | 2013-11-12 11:32:41 -0800 | [diff] [blame] | 5 | Copyright 2013 The Android Open Source Project |
Clay Murphy | 47b1d3f | 2013-10-03 10:02:22 -0700 | [diff] [blame] | 6 | |
| 7 | Licensed under the Apache License, Version 2.0 (the "License"); |
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| 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> |
| 28 | This page exlains how to implement the audio Hardware Abstraction Layer (HAL) |
| 29 | and configure the shared library. |
| 30 | </p> |
| 31 | |
| 32 | <h2 id="implementing"> |
| 33 | Implementing the HAL |
| 34 | </h2> |
| 35 | <p> |
| 36 | The audio HAL is composed of three different interfaces that you must implement: |
| 37 | </p> |
| 38 | <ul> |
| 39 | <li> |
| 40 | <code>hardware/libhardware/include/hardware/audio.h</code> - represents the main functions of |
| 41 | an audio device. |
| 42 | </li> |
| 43 | <li> |
| 44 | <code>hardware/libhardware/include/hardware/audio_policy.h</code> - represents the audio policy |
| 45 | manager, which handles things like audio routing and volume control policies. |
| 46 | </li> |
| 47 | <li> |
| 48 | <code>hardware/libhardware/include/hardware/audio_effect.h</code> - represents effects that can |
| 49 | be applied to audio such as downmixing, echo, or noise suppression. |
| 50 | </li> |
| 51 | </ul> |
| 52 | <p>See the implementation for the Galaxy Nexus at <code>device/samsung/tuna/audio</code> for an example.</p> |
| 53 | |
| 54 | <p>In addition to implementing the HAL, you need to create a |
| 55 | <code>device/<company_name>/<device_name>/audio/audio_policy.conf</code> file |
| 56 | that declares the audio devices present on your product. For an example, see the file for |
| 57 | the Galaxy Nexus audio hardware in <code>device/samsung/tuna/audio/audio_policy.conf</code>. |
| 58 | Also, see |
| 59 | the <code>system/core/include/system/audio.h</code> and <code>system/core/include/system/audio_policy.h</code> |
| 60 | header files for a reference of the properties that you can define. |
| 61 | </p> |
| 62 | <h3 id="multichannel">Multi-channel support</h3> |
| 63 | <p>If your hardware and driver supports multichannel audio via HDMI, you can output the audio stream |
| 64 | directly to the audio hardware. This bypasses the AudioFlinger mixer so it doesn't get downmixed to two channels. |
| 65 | |
| 66 | <p> |
| 67 | The audio HAL must expose whether an output stream profile supports multichannel audio capabilities. |
| 68 | If the HAL exposes its capabilities, the default policy manager allows multichannel playback over |
| 69 | HDMI.</p> |
| 70 | <p>For more implementation details, see the |
| 71 | <code>device/samsung/tuna/audio/audio_hw.c</code> in the Android 4.1 release.</p> |
| 72 | |
| 73 | <p> |
| 74 | To specify that your product contains a multichannel audio output, edit the <code>audio_policy.conf</code> file to describe the multichannel |
| 75 | output for your product. The following is an example from the Galaxy Nexus that shows a "dynamic" channel mask, which means the audio policy manager |
| 76 | queries the actual channel masks supported by the HDMI sink after connection. You can also specify a static channel mask like <code>AUDIO_CHANNEL_OUT_5POINT1</code> |
| 77 | </p> |
| 78 | <pre> |
| 79 | audio_hw_modules { |
| 80 | primary { |
| 81 | outputs { |
| 82 | ... |
| 83 | hdmi { |
| 84 | sampling_rates 44100|48000 |
| 85 | channel_masks dynamic |
| 86 | formats AUDIO_FORMAT_PCM_16_BIT |
| 87 | devices AUDIO_DEVICE_OUT_AUX_DIGITAL |
| 88 | flags AUDIO_OUTPUT_FLAG_DIRECT |
| 89 | } |
| 90 | ... |
| 91 | } |
| 92 | ... |
| 93 | } |
| 94 | ... |
| 95 | } |
| 96 | </pre> |
| 97 | |
| 98 | |
| 99 | <p>AudioFlinger's mixer downmixes the content to stereo |
| 100 | automatically when sent to an audio device that does not support multichannel audio.</p> |
Clay Murphy | 47b1d3f | 2013-10-03 10:02:22 -0700 | [diff] [blame] | 101 | |
| 102 | <h3 id="codecs">Media codecs</h3> |
| 103 | |
| 104 | <p>Ensure the audio codecs your hardware and drivers support are properly declared for your product. See |
| 105 | <a href="media.html#expose"> Exposing Codecs to the Framework</a> for information on how to do this. |
| 106 | </p> |
| 107 | |
| 108 | <h2 id="configuring"> |
| 109 | Configuring the shared library |
| 110 | </h2> |
| 111 | <p> |
| 112 | You need to package the HAL implementation into a shared library and copy it to the |
| 113 | appropriate location by creating an <code>Android.mk</code> file: |
| 114 | </p> |
| 115 | <ol> |
| 116 | <li>Create a <code>device/<company_name>/<device_name>/audio</code> directory |
| 117 | to contain your library's source files. |
| 118 | </li> |
| 119 | <li>Create an <code>Android.mk</code> file to build the shared library. Ensure that the |
| 120 | Makefile contains the following line: |
| 121 | <pre> |
| 122 | LOCAL_MODULE := audio.primary.<device_name> |
| 123 | </pre> |
| 124 | <p> |
| 125 | Notice your library must be named <code>audio_primary.<device_name>.so</code> so |
| 126 | that Android can correctly load the library. The "<code>primary</code>" portion of this |
| 127 | filename indicates that this shared library is for the primary audio hardware located on the |
| 128 | device. The module names <code>audio.a2dp.<device_name></code> and |
| 129 | <code>audio.usb.<device_name></code> are also available for bluetooth and USB audio |
| 130 | interfaces. Here is an example of an <code>Android.mk</code> from the Galaxy |
| 131 | Nexus audio hardware: |
| 132 | </p> |
| 133 | <pre> |
| 134 | LOCAL_PATH := $(call my-dir) |
| 135 | |
| 136 | include $(CLEAR_VARS) |
| 137 | |
| 138 | LOCAL_MODULE := audio.primary.tuna |
Clay Murphy | f8f77d7 | 2014-03-11 20:45:20 +0000 | [diff] [blame] | 139 | LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw |
Clay Murphy | 47b1d3f | 2013-10-03 10:02:22 -0700 | [diff] [blame] | 140 | LOCAL_SRC_FILES := audio_hw.c ril_interface.c |
| 141 | LOCAL_C_INCLUDES += \ |
| 142 | external/tinyalsa/include \ |
| 143 | $(call include-path-for, audio-utils) \ |
| 144 | $(call include-path-for, audio-effects) |
| 145 | LOCAL_SHARED_LIBRARIES := liblog libcutils libtinyalsa libaudioutils libdl |
| 146 | LOCAL_MODULE_TAGS := optional |
| 147 | |
| 148 | include $(BUILD_SHARED_LIBRARY) |
| 149 | </pre> |
| 150 | </li> |
| 151 | <li>If your product supports low latency audio as specified by the Android CDD, copy the |
| 152 | corresponding XML feature file into your product. For example, in your product's |
| 153 | <code>device/<company_name>/<device_name>/device.mk</code> |
| 154 | Makefile: |
| 155 | <pre> |
| 156 | PRODUCT_COPY_FILES := ... |
| 157 | |
| 158 | PRODUCT_COPY_FILES += \ |
| 159 | frameworks/native/data/etc/android.android.hardware.audio.low_latency.xml:system/etc/permissions/android.hardware.audio.low_latency.xml \ |
| 160 | </pre> |
| 161 | </li> |
| 162 | |
| 163 | <li>Copy the <code>audio_policy.conf</code> file that you created earlier to the <code>system/etc/</code> directory |
| 164 | in your product's <code>device/<company_name>/<device_name>/device.mk</code> |
| 165 | Makefile. For example: |
| 166 | <pre> |
| 167 | PRODUCT_COPY_FILES += \ |
| 168 | device/samsung/tuna/audio/audio_policy.conf:system/etc/audio_policy.conf |
| 169 | </pre> |
| 170 | </li> |
| 171 | <li>Declare the shared modules of your audio HAL that are required by your product in the product's |
| 172 | <code>device/<company_name>/<device_name>/device.mk</code> Makefile. For example, the |
| 173 | Galaxy Nexus requires the primary and bluetooth audio HAL modules: |
| 174 | <pre> |
| 175 | PRODUCT_PACKAGES += \ |
| 176 | audio.primary.tuna \ |
| 177 | audio.a2dp.default |
| 178 | </pre> |
| 179 | </li> |
| 180 | </ol> |
| 181 | |
| 182 | <h2 id="preprocessing">Audio pre-processing effects</h2> |
| 183 | <p> |
| 184 | The Android platform provides audio effects on supported devices in the |
| 185 | <a href="http://developer.android.com/reference/android/media/audiofx/package-summary.html">audiofx</a> |
| 186 | package, which is available for developers to access. For example, on the Nexus 10, the following pre-processing effects are supported: </p> |
| 187 | <ul> |
| 188 | <li><a |
| 189 | href="http://developer.android.com/reference/android/media/audiofx/AcousticEchoCanceler.html">Acoustic Echo Cancellation</a></li> |
| 190 | <li><a |
| 191 | href="http://developer.android.com/reference/android/media/audiofx/AutomaticGainControl.html">Automatic Gain Control</a></li> |
| 192 | <li><a |
| 193 | href="http://developer.android.com/reference/android/media/audiofx/NoiseSuppressor.html">Noise Suppression</a></li> |
| 194 | </ul> |
Clay Murphy | 47b1d3f | 2013-10-03 10:02:22 -0700 | [diff] [blame] | 195 | |
| 196 | |
| 197 | <p>Pre-processing effects are always paired with the use case mode in which the pre-processing is requested. In Android |
| 198 | app development, a use case is referred to as an <code>AudioSource</code>; and app developers |
| 199 | request to use the <code>AudioSource</code> abstraction instead of the actual audio hardware device. |
| 200 | The Android Audio Policy Manager maps an <code>AudioSource</code> to the actual hardware with <code>AudioPolicyManagerBase::getDeviceForInputSource(int |
| 201 | inputSource)</code>. The following sources are exposed to developers: |
| 202 | </p> |
| 203 | <ul> |
Glenn Kasten | 795a9de | 2014-01-24 08:58:56 -0800 | [diff] [blame] | 204 | <li><code>android.media.MediaRecorder.AudioSource.CAMCORDER</code></li> |
| 205 | <li><code>android.media.MediaRecorder.AudioSource.VOICE_COMMUNICATION</code></li> |
| 206 | <li><code>android.media.MediaRecorder.AudioSource.VOICE_CALL</code></li> |
| 207 | <li><code>android.media.MediaRecorder.AudioSource.VOICE_DOWNLINK</code></li> |
| 208 | <li><code>android.media.MediaRecorder.AudioSource.VOICE_UPLINK</code></li> |
| 209 | <li><code>android.media.MediaRecorder.AudioSource.VOICE_RECOGNITION</code></li> |
| 210 | <li><code>android.media.MediaRecorder.AudioSource.MIC</code></li> |
| 211 | <li><code>android.media.MediaRecorder.AudioSource.DEFAULT</code></li> |
Clay Murphy | 47b1d3f | 2013-10-03 10:02:22 -0700 | [diff] [blame] | 212 | </ul> |
| 213 | |
| 214 | <p>The default pre-processing effects that are applied for each <code>AudioSource</code> are |
| 215 | specified in the <code>/system/etc/audio_effects.conf</code> file. To specify |
| 216 | your own default effects for every <code>AudioSource</code>, create a <code>/system/vendor/etc/audio_effects.conf</code> file |
| 217 | and specify any pre-processing effects that you need to turn on. For an example, |
| 218 | see the implementation for the Nexus 10 in <code>device/samsung/manta/audio_effects.conf</code></p> |
| 219 | |
| 220 | <p class="warning"><strong>Warning:</strong> For the <code>VOICE_RECOGNITION</code> use case, do not enable |
| 221 | the noise suppression pre-processing effect. It should not be turned on by default when recording from this audio source, |
| 222 | and you should not enable it in your own audio_effects.conf file. Turning on the effect by default will cause the device to fail |
| 223 | the <a href="/compatibility/index.html">compatibility requirement</a> regardless of whether this was on by default due to |
| 224 | configuration file, or the audio HAL implementation's default behavior.</p> |
| 225 | |
| 226 | <p>The following example enables pre-processing for the VoIP <code>AudioSource</code> and Camcorder <code>AudioSource</code>. |
| 227 | By declaring the <code>AudioSource</code> configuration in this manner, the |
| 228 | framework will automatically request from the audio HAL the use of those |
| 229 | effects.</p> |
| 230 | |
| 231 | <pre> |
| 232 | pre_processing { |
| 233 | voice_communication { |
| 234 | aec {} |
| 235 | ns {} |
| 236 | } |
| 237 | camcorder { |
| 238 | agc {} |
| 239 | } |
| 240 | } |
| 241 | </pre> |
| 242 | |
| 243 | <h3 id="tuning">Source tuning</h3> |
| 244 | <p>For <code>AudioSource</code> tuning, there are no explicit requirements on audio gain or audio processing |
| 245 | with the exception of voice recognition (<code>VOICE_RECOGNITION</code>).</p> |
| 246 | |
| 247 | <p>The following are the requirements for voice recognition:</p> |
| 248 | |
| 249 | <ul> |
| 250 | <li>"flat" frequency response (+/- 3dB) from 100Hz to 4kHz</li> |
| 251 | <li>close-talk config: 90dB SPL reads RMS of 2500 (16bit samples)</li> |
| 252 | <li>level tracks linearly from -18dB to +12dB relative to 90dB SPL</li> |
| 253 | <li>THD < 1% (90dB SPL in 100 to 4000Hz range)</li> |
| 254 | <li>8kHz sampling rate (anti-aliasing)</li> |
| 255 | <li>Effects / pre-processing must be disabled by default</li> |
| 256 | </ul> |
| 257 | |
| 258 | <p>Examples of tuning different effects for different sources are:</p> |
| 259 | |
| 260 | <ul> |
| 261 | <li>Noise Suppressor |
| 262 | <ul> |
| 263 | <li>Tuned for wind noise suppressor for <code>CAMCORDER</code></li> |
| 264 | <li>Tuned for stationary noise suppressor for <code>VOICE_COMMUNICATION</code></li> |
| 265 | </ul> |
| 266 | </li> |
| 267 | <li>Automatic Gain Control |
| 268 | <ul> |
| 269 | <li>Tuned for close-talk for <code>VOICE_COMMUNICATION</code> and main phone mic</li> |
| 270 | <li>Tuned for far-talk for <code>CAMCORDER</code></li> |
| 271 | </ul> |
| 272 | </li> |
| 273 | </ul> |
| 274 | |
| 275 | <h3 id="more">More information</h3> |
| 276 | <p>For more information, see:</p> |
| 277 | <ul> |
| 278 | <li>Android documentation for <a href="http://developer.android.com/reference/android/media/audiofx/package-summary.html">audiofx |
| 279 | package</a> |
| 280 | |
| 281 | <li>Android documentation for <a href="http://developer.android.com/reference/android/media/audiofx/NoiseSuppressor.html">Noise Suppression audio effect</a></li> |
| 282 | <li><code>device/samsung/manta/audio_effects.conf</code> file for the Nexus 10</li> |
| 283 | </ul> |