session-android/res/drawable/webrtc_audio_button.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:id="@+id/compoundBackgroundItem" android:drawable="@drawable/webrtc_control_background"/>

    <item android:id="@+id/moreIndicatorItem"
          android:top="5dp"
          android:left="5dp"
          android:right="5dp"
          android:bottom="5dp">
        <bitmap android:src="@drawable/redphone_ic_more_indicator_holo_dark"
                android:gravity="bottom|right" />
    </item>

    <item android:id="@+id/bluetoothItem"
          android:top="5dp"
          android:left="5dp"
          android:right="5dp"
          android:bottom="5dp">
        <bitmap android:src="@drawable/ic_phone_bluetooth_speaker_white_24dp"
                android:gravity="center" />
    </item>

    <!-- Handset earpiece is active -->
    <item android:id="@+id/handsetItem" android:top="5dp"
          android:left="5dp"
          android:right="5dp"
          android:bottom="5dp">
        <bitmap android:src="@drawable/ic_phone_in_talk_white_24dp"
                android:gravity="center" />
    </item>

    <!-- Speakerphone icon showing 'speaker on' state -->
    <item android:id="@+id/speakerphoneOnItem" android:top="5dp"
          android:left="5dp"
          android:right="5dp"
          android:bottom="5dp">
        <bitmap android:src="@drawable/ic_volume_up_white_24dp"
                android:gravity="center" />
    </item>

    <!--&lt;!&ndash; Speakerphone icon showing 'speaker off' state &ndash;&gt;-->
    <!--<item android:id="@+id/speakerphoneOffItem">-->
        <!--<bitmap android:src="@drawable/ic_volume_mute_white_24dp"-->
                <!--android:gravity="center" />-->
    <!--</item>-->

</layer-list>