session-android/res/layout/webrtc_call_controls.xml

<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android"
                    xmlns:tools="http://schemas.android.com/tools"
              android:id="@+id/inCallControls"
              android:layout_width="wrap_content"
              android:layout_height="wrap_content"
              android:orientation="horizontal"
              tools:background="@color/textsecure_primary">

        <ToggleButton android:id="@+id/speakerButton"
                      style="@style/WebRtcCallCompoundButton"
                      android:background="@drawable/webrtc_speaker_button"
                      tools:checked="true"
                      android:layout_marginRight="15dp"/>

        <ToggleButton android:id="@+id/bluetoothButton"
                      style="@style/WebRtcCallCompoundButton"
                      android:background="@drawable/webrtc_bluetooth_button"
                      tools:checked="true"
                      android:layout_marginRight="15dp"
                      android:visibility="gone"/>

        <ToggleButton android:id="@+id/muteButton"
                      style="@style/WebRtcCallCompoundButton"
                      android:background="@drawable/webrtc_mute_button"
                      android:contentDescription="@string/redphone_call_controls__mute"
                      android:layout_marginRight="15dp"
                      tools:checked="false"
                />

        <ToggleButton android:id="@+id/video_mute_button"
                      style="@style/WebRtcCallCompoundButton"
                      android:background="@drawable/webrtc_video_mute_button"/>

</merge>