android_frameworks_base/docs/html/training/managing-audio/volume-playback.jd

page.title=Controlling Your App’s Volume and Playback
parent.title=Managing Audio Playback
parent.link=index.html

trainingnavtop=true
next.title=Managing Audio Focus
next.link=audio-focus.html

@jd:body

 
<div id="tb-wrapper"> 
<div id="tb">

<h2>This lesson teaches you to</h2>
<ol>
  <li><a href="#IdentifyStream">Identify Which Audio Stream to Use</a></li>
  <li><a href="#HardwareVolumeKeys">Use Hardware Volume Keys to Control Your App’s Audio
Volume</a></li>
  <li><a href="#PlaybackControls">Use Hardware Playback Control Keys to Control Your App’s Audio
Playback</a></li>
</ol>

<h2>You should also read</h2>
<ul>
  <li><a href="{@docRoot}guide/topics/media/mediaplayer.html">Media Playback</a></li>
</ul>

</div> 
</div>


 
<p>A good user experience is a predictable one. If your app plays media it’s important that your
users can control the volume of your app using the hardware or software volume controls of their
device, bluetooth headset, or headphones.</p>

<p>Similarly, where appropriate and available, the play, stop, pause, skip, and previous media
playback keys should perform their respective actions on the audio stream used by your app.</p>

 
<h2 id="IdentifyStream">Identify Which Audio Stream to Use</h2> 
 
<p>The first step to creating a predictable audio experience is understanding which audio stream
your app will use.</p>

<p>Android maintains a separate audio stream for playing music, alarms, notifications, the incoming
call ringer, system sounds, in-call volume, and DTMF tones. This is done primarily to allow users to
control the volume of each stream independently.</p>

<p>Most of these streams are restricted to system events, so unless your app is a replacement alarm
clock, you’ll almost certainly be playing your audio using the {@link
android.media.AudioManager#STREAM_MUSIC} stream.</p>


<h2 id="HardwareVolumeKeys">Use Hardware Volume Keys to Control Your App’s Audio Volume</h2> 

<p>By default, pressing the volume controls modify the volume of the active audio stream. If your
app isn't currently playing anything, hitting the volume keys adjusts the ringer volume.<p>
    
<p>If you've got a game or music app, then chances are good that when the user hits the volume keys
they want to control the volume of the game or music, even if they’re currently between songs or
there’s no music in the current game location.</p>

<p>You may be tempted to try and listen for volume key presses and modify the volume of your
audio stream that way. Resist the urge. Android provides the handy {@link
android.app.Activity#setVolumeControlStream setVolumeControlStream()} method to direct volume key
presses to the audio stream you specify.<p> 
  
<p>Having identified the audio stream your application
will be using, you should set it as the volume stream target. You should make this call early in
your app’s lifecycle&mdash;because you only need to call it once during the activity lifecycle, you
should typically call it within the {@code onCreate()} method (of the {@link
android.app.Activity} or {@link android.app.Fragment} that controls
your media). This ensures that whenever your app is visible, the
volume controls function as the user expects.<p>

<pre>
setVolumeControlStream(AudioManager.STREAM_MUSIC);
</pre>


<p>From this point onwards, pressing the volume keys on the device affect the audio stream you
specify (in this case “music”) whenever the target activity or fragment is visible.</p>


<h2 id="PlaybackControls">Use Hardware Playback Control Keys to Control Your App’s Audio
Playback</h2> 

<p>Media playback buttons such as play, pause, stop, skip, and previous are available on some
handsets and many connected or wireless headsets. Whenever a user presses one of these hardware
keys, the system broadcasts an intent with the {@link android.content.Intent#ACTION_MEDIA_BUTTON}
action.</p>

<p>To respond to media button clicks, you need to register a {@link
android.content.BroadcastReceiver} in your manifest that listens for this action broadcast as shown
below.</p>

<pre>
&lt;receiver android:name=".RemoteControlReceiver">
    &lt;intent-filter>
        &lt;action android:name="android.intent.action.MEDIA_BUTTON" />
    &lt;/intent-filter>
&lt;/receiver>
</pre>

<p>The receiver implementation itself needs to extract which key was pressed to cause the broadcast.
The {@link android.content.Intent} includes this under the {@link
android.content.Intent#EXTRA_KEY_EVENT} key, while the {@link android.view.KeyEvent} class includes
a list {@code KEYCODE_MEDIA_*} static constants that represents each of the possible media
buttons, such as {@link android.view.KeyEvent#KEYCODE_MEDIA_PLAY_PAUSE} and {@link
android.view.KeyEvent#KEYCODE_MEDIA_NEXT}.</p>

<p>The following snippet shows how to extract the media button pressed and affects the media playback accordingly.</p>

<pre>
public class RemoteControlReceiver extends BroadcastReceiver {
    &#64;Override
    public void onReceive(Context context, Intent intent) {
        if (Intent.ACTION_MEDIA_BUTTON.equals(intent.getAction())) {
            KeyEvent event = (KeyEvent)intent.getParcelableExtra(Intent.EXTRA_KEY_EVENT);
            if (KeyEvent.KEYCODE_MEDIA_PLAY == event.getKeyCode()) {
                // Handle key press.
            }
        }
    }
}
</pre>

<p>Because multiple applications might want to listen for media button presses, you must
also programmatically control when your app should receive media button press events.</p>

<p>The following code can be used within your app to register and de-register your media button
event receiver using the {@link android.media.AudioManager}. When registered, your broadcast
receiver is the exclusive receiver of all media button broadcasts.<p>

<pre>
AudioManager am = mContext.getSystemService(Context.AUDIO_SERVICE);
...

// Start listening for button presses
am.registerMediaButtonEventReceiver(RemoteControlReceiver);
...

// Stop listening for button presses
am.unregisterMediaButtonEventReceiver(RemoteControlReceiver);
</pre>

<p>Typically, apps should unregister most of their receivers whenever they become inactive or
invisible (such as during the {@link android.app.Activity#onStop onStop()} callback). However, it’s
not that simple for media playback apps&mdash;in fact, responding to media playback buttons is most
important when your application isn’t visible and therefore can’t be controlled by the on-screen
UI.</p>

<p>A better approach is to register and unregister the media button event receiver when your
application gains and losses the audio focus. This is covered in detail in the next lesson.</p>