en/devices/automotive/audio/interaction-sequences.html - platform/docs/source.android.com - Git at Google

 <html devsite>
   <head>
     <title>Example Interaction Sequences</title>
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     <meta name="book_path" value="/_book.yaml" />
   </head>
   {% include "_versions.html" %}
   <body>
   <!--
       Copyright 2018 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.
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       distributed under the License is distributed on an "AS IS" BASIS,
       WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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 <p>
   In the following automotive audio examples, the vehicle head unit runs
   Android {{ androidPVersionNumber }} and includes a radio application and a
   navigation application. In addition, the vehicle tuner is externally routed
   and plays over the speakers. In real-world use cases, it may be advantageous
   to handle the tuner as an input to Android and have the Radio app read from
   the tuner and write to an <code>AudioTrack</code> object.
 </p>

 <h2 id="user-starts-radio">User starts radio</h2>

 <p>
   In this interaction sequence, no media is playing in the vehicle when the user
   presses <strong>Play</strong> for a preset frequency in the radio application.
   The radio application must gain focus for the tuner to play sound over the
   speakers.
 </p>

 <p><img src="/devices/automotive/images/audio_auto_focus_radio.png"></p>
 <figcaption><strong>Figure 1.</strong> Radio gains focus and tuner play over
 speakers</figcaption>

 <ol>
   <li>Radio: "Tune to FM 96.5."</li>
   <li>Radio: Request focus GAIN.</li>
   <li>AudioManager: GAIN granted.</li>
   <li>Radio: <code>createAudioPatch()</code></li>
   <li>Radio: "Play tuner output."</li>
   <li>Externally-routed tuner: Mixer enables Tuner audio route to amplifier.
   </li>
 </ol>

 <h2 id="radio-ducks-nav-prompt">Radio ducks navigation prompt</h2>

 <p>
   In this interaction sequence, the radio is playing when the navigation
   application generates a navigation prompt for a next turn announcement. The
   navigation application must obtain transient focus from the
   <code>AudioManager</code> to play the navigation prompt.
 </p>

 <p><img src="/devices/automotive/images/audio_auto_radio_ducks.png"></p>
 <figcaption><strong>Figure 2.</strong> Radio playback ducks navigation
 prompt</figcaption>

 <ol>
   <li value="5">Radio: "Play tuner output."</li>
   <li>Externally-routed tuner: Mixer enables Tuner audio route to amplifier.
   </li>
   <li>Navigation: Request focus GAIN TRANSIENT from <code>AudioManager</code>.
   </li>
   <li>AudioManager: GAIN TRANSIENT to Navigation.</li>
   <li>Navigation: Open stream, send packets.
     <ol>
     <li>Navigation: Context GUIDANCE routed on bus1.</li>
     <li>Mixer: Ducks Tuner to play bus1 GUIDANCE on Speakers.</li>
     </ol>
   </li>
   <li>Navigation: Announcement over, close stream.</li>
   <li>Navigation: Abandon focus.</li>
 </ol>

 <p>
   The <code>AudioManager</code> recognizes the radio playback can duck and would
   normally apply a ducking factor to the music stream without notifying the
   radio application. However, the framework ducking is bypassed by overlaying
   <code>framework/base/core/res/res/values/config.xml</code> and setting
   <code>config_applyInternalDucking</code> to <code>false</code>, so the
   external tuner continues to provide sound and the radio application remains
   unaware of any changes. The mixer (below the HAL) is responsible for combining
   the two inputs and can choose to duck radio playback or move radio playback to
   the rear speakers.
 </p>

 <p>
   When the navigation prompt is complete, the navigation application releases
   focus and radio playback resumes.
 </p>

 <h2 id="user-launches-audio-book">User launches audio book application</h2>

 <p>
   In this interaction sequence, the user launches an audio book application,
   causing radio playback to stop (pressing play in a streaming music app would
   be a similar trigger).
 </p>

 <p><img src="/devices/automotive/images/audio_auto_focus_book.png"></p>
 <figcaption><strong>Figure 3.</strong> Audio book takes focus from radio
 playback</figcaption>

 <ol>
   <li value="12">Audio Book: Request GAIN context MEDIA from
   <code>AudioManager</code>.</li>
   <li>Radio loses focus:
     <ol>
     <li>AudioManager: LOSS.</li>
     <li>Radio: <code>releaseAudioPatch()</code></li>
     </ol>
   </li>
   <li>Audio Book gains focus:
     <ol>
     <li>GAIN granted, Context MEDIA routed on bus0</li>
     <li>Open stream, send MEDIA packets.</li>
     </ol>
   </li>
 </ol>

 <p>
   The request for focus by the audio book application is not transient, and so
   the previous focus holder (the radio application), receives a permanent focus
   loss, to which the radio application responds by tearing down the patch to the
   tuner. The mixer stops listening to the tuner and starts processing the audio
   delivered via the Audio HAL (it may also optionally perform a cross fade as
   part of the radio-to-audiobook transition).
 </p>

 <h2 id="nav-prompt-takes-focus">Navigation prompt takes focus</h2>

 <p>
   In this interaction sequence, the audio book is playing when the navigation
   application generates a navigation prompt.
 </p>

 <p><img src="/devices/automotive/images/audio_auto_focus_nav.png"></p>
 <figcaption><strong>Figure 4.</strong> Navigation prompt takes focus from audio
 book playback</figcaption>

 <ol>
   <li value="15">Audio Book: Streaming MEDIA packets, focus no-concurrent.</li>
   <li>Navigation: Request GAIN TRANSIENT.</li>
   <li>AudioManager: LOSS TRANSIENT.</li>
   <li>Audio Book: Stops.</li>
   <li>Audio Manager: GAIN TRANSIENT granted.</li>
   <li>Navigation: Open stream, send packets.
     <ol>
     <li>Navigation: Context GUIDANCE routed on bus1.</li>
     <li>Mixer: Plays bus1 (GUIDANCE).</li>
     </ol>
   </li>
   <li>Navigation: Announcement over, close stream.</li>
   <li>Navigation: Abandon focus.</li>
   <li>Audio Book: GAIN.</li>
   <li>Audio Book: Restarts.</li>
 </ol>

 <p>
   Because the original audio book application <code>AudioFocusRequest</code>
   (sent when starting the <code>AudioTrack</code>) included the
   <code>AUDIOFOCUS_FLAG_PAUSES_ON_DUCKABLE_LOSS</code> flag, the
   <code>AudioManager</code> determines it cannot handle ducking for the audio
   book app. Instead, <code>AudioManager</code> sends an
   <code>AUDIOFOCUS_LOSS_TRANSIENT</code> message to the audio book app, which is
   expected to respond by suspending its playback.
 </p>

 <p>
   The navigation application can now play the navigation prompt without
   interruption. When the navigation prompt is complete, the audio book regains
   focus and resumes playback.
 </p>

 </body>
 </html>
	<html devsite>
	<head>
	<title>Example Interaction Sequences</title>
	<meta name="project_path" value="/_project.yaml" />
	<meta name="book_path" value="/_book.yaml" />
	</head>
	{% include "_versions.html" %}
	<body>
	<!--
	Copyright 2018 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>
	In the following automotive audio examples, the vehicle head unit runs
	Android {{ androidPVersionNumber }} and includes a radio application and a
	navigation application. In addition, the vehicle tuner is externally routed
	and plays over the speakers. In real-world use cases, it may be advantageous
	to handle the tuner as an input to Android and have the Radio app read from
	the tuner and write to an <code>AudioTrack</code> object.
	</p>

	<h2 id="user-starts-radio">User starts radio</h2>

	<p>
	In this interaction sequence, no media is playing in the vehicle when the user
	presses <strong>Play</strong> for a preset frequency in the radio application.
	The radio application must gain focus for the tuner to play sound over the
	speakers.
	</p>

	<p><img src="/devices/automotive/images/audio_auto_focus_radio.png"></p>
	<figcaption><strong>Figure 1.</strong> Radio gains focus and tuner play over
	speakers</figcaption>

	<ol>
	<li>Radio: "Tune to FM 96.5."</li>
	<li>Radio: Request focus GAIN.</li>
	<li>AudioManager: GAIN granted.</li>
	<li>Radio: <code>createAudioPatch()</code></li>
	<li>Radio: "Play tuner output."</li>
	<li>Externally-routed tuner: Mixer enables Tuner audio route to amplifier.
	</li>
	</ol>

	<h2 id="radio-ducks-nav-prompt">Radio ducks navigation prompt</h2>

	<p>
	In this interaction sequence, the radio is playing when the navigation
	application generates a navigation prompt for a next turn announcement. The
	navigation application must obtain transient focus from the
	<code>AudioManager</code> to play the navigation prompt.
	</p>

	<p><img src="/devices/automotive/images/audio_auto_radio_ducks.png"></p>
	<figcaption><strong>Figure 2.</strong> Radio playback ducks navigation
	prompt</figcaption>

	<ol>
	<li value="5">Radio: "Play tuner output."</li>
	<li>Externally-routed tuner: Mixer enables Tuner audio route to amplifier.
	</li>
	<li>Navigation: Request focus GAIN TRANSIENT from <code>AudioManager</code>.
	</li>
	<li>AudioManager: GAIN TRANSIENT to Navigation.</li>
	<li>Navigation: Open stream, send packets.
	<ol>
	<li>Navigation: Context GUIDANCE routed on bus1.</li>
	<li>Mixer: Ducks Tuner to play bus1 GUIDANCE on Speakers.</li>
	</ol>
	</li>
	<li>Navigation: Announcement over, close stream.</li>
	<li>Navigation: Abandon focus.</li>
	</ol>

	<p>
	The <code>AudioManager</code> recognizes the radio playback can duck and would
	normally apply a ducking factor to the music stream without notifying the
	radio application. However, the framework ducking is bypassed by overlaying
	<code>framework/base/core/res/res/values/config.xml</code> and setting
	<code>config_applyInternalDucking</code> to <code>false</code>, so the
	external tuner continues to provide sound and the radio application remains
	unaware of any changes. The mixer (below the HAL) is responsible for combining
	the two inputs and can choose to duck radio playback or move radio playback to
	the rear speakers.
	</p>

	<p>
	When the navigation prompt is complete, the navigation application releases
	focus and radio playback resumes.
	</p>

	<h2 id="user-launches-audio-book">User launches audio book application</h2>

	<p>
	In this interaction sequence, the user launches an audio book application,
	causing radio playback to stop (pressing play in a streaming music app would
	be a similar trigger).
	</p>

	<p><img src="/devices/automotive/images/audio_auto_focus_book.png"></p>
	<figcaption><strong>Figure 3.</strong> Audio book takes focus from radio
	playback</figcaption>

	<ol>
	<li value="12">Audio Book: Request GAIN context MEDIA from
	<code>AudioManager</code>.</li>
	<li>Radio loses focus:
	<ol>
	<li>AudioManager: LOSS.</li>
	<li>Radio: <code>releaseAudioPatch()</code></li>
	</ol>
	</li>
	<li>Audio Book gains focus:
	<ol>
	<li>GAIN granted, Context MEDIA routed on bus0</li>
	<li>Open stream, send MEDIA packets.</li>
	</ol>
	</li>
	</ol>

	<p>
	The request for focus by the audio book application is not transient, and so
	the previous focus holder (the radio application), receives a permanent focus
	loss, to which the radio application responds by tearing down the patch to the
	tuner. The mixer stops listening to the tuner and starts processing the audio
	delivered via the Audio HAL (it may also optionally perform a cross fade as
	part of the radio-to-audiobook transition).
	</p>

	<h2 id="nav-prompt-takes-focus">Navigation prompt takes focus</h2>

	<p>
	In this interaction sequence, the audio book is playing when the navigation
	application generates a navigation prompt.
	</p>

	<p><img src="/devices/automotive/images/audio_auto_focus_nav.png"></p>
	<figcaption><strong>Figure 4.</strong> Navigation prompt takes focus from audio
	book playback</figcaption>

	<ol>
	<li value="15">Audio Book: Streaming MEDIA packets, focus no-concurrent.</li>
	<li>Navigation: Request GAIN TRANSIENT.</li>
	<li>AudioManager: LOSS TRANSIENT.</li>
	<li>Audio Book: Stops.</li>
	<li>Audio Manager: GAIN TRANSIENT granted.</li>
	<li>Navigation: Open stream, send packets.
	<ol>
	<li>Navigation: Context GUIDANCE routed on bus1.</li>
	<li>Mixer: Plays bus1 (GUIDANCE).</li>
	</ol>
	</li>
	<li>Navigation: Announcement over, close stream.</li>
	<li>Navigation: Abandon focus.</li>
	<li>Audio Book: GAIN.</li>
	<li>Audio Book: Restarts.</li>
	</ol>

	<p>
	Because the original audio book application <code>AudioFocusRequest</code>
	(sent when starting the <code>AudioTrack</code>) included the
	<code>AUDIOFOCUS_FLAG_PAUSES_ON_DUCKABLE_LOSS</code> flag, the
	<code>AudioManager</code> determines it cannot handle ducking for the audio
	book app. Instead, <code>AudioManager</code> sends an
	<code>AUDIOFOCUS_LOSS_TRANSIENT</code> message to the audio book app, which is
	expected to respond by suspending its playback.
	</p>

	<p>
	The navigation application can now play the navigation prompt without
	interruption. When the navigation prompt is complete, the audio book regains
	focus and resumes playback.
	</p>

	</body>
	</html>