element-android/vector/src/main/res/layout/activity_call.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- tools:ignore is needed because lint thinks this can be replaced with a merge. Replacing this
     with a merge causes the fullscreen SurfaceView not to be centered. -->
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:ignore="MergeRootFrame">

    <org.webrtc.SurfaceViewRenderer
        android:id="@+id/fullscreen_video_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="center" />

    <org.webrtc.SurfaceViewRenderer
        android:id="@+id/pip_video_view"
        android:layout_width="wrap_content"
        android:layout_height="144dp"
        android:layout_gravity="bottom|end"
        android:layout_margin="16dp" />

    <ImageView
        android:id="@+id/iv_end_call"
        android:layout_width="64dp"
        android:layout_height="64dp"
        android:src="@drawable/ic_call_end"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:layout_marginBottom="32dp"
        app:layout_constraintBottom_toTopOf="@+id/layout_call_actions"/>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/layout_call_actions"
        android:layout_width="match_parent"
        android:layout_height="80dp"
        android:layout_marginBottom="48dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:background="@drawable/bg_call_actions">

        <ImageView
            android:id="@+id/iv_call_speaker"
            android:layout_width="32dp"
            android:layout_height="32dp"
            android:src="@drawable/ic_call_speaker_default"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            android:layout_marginStart="32dp"/>

        <ImageView
            android:id="@+id/iv_call_flip_camera"
            android:layout_width="32dp"
            android:layout_height="32dp"
            android:src="@drawable/ic_call_flip_camera_default"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            android:layout_marginStart="32dp"/>

        <ImageView
            android:id="@+id/iv_call_videocam_off"
            android:layout_width="32dp"
            android:layout_height="32dp"
            android:src="@drawable/ic_call_videocam_off_default"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent" />

        <ImageView
            android:id="@+id/iv_call_mute"
            android:layout_width="32dp"
            android:layout_height="32dp"
            android:src="@drawable/ic_call_mute_default"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            android:layout_marginEnd="32dp"/>

    </androidx.constraintlayout.widget.ConstraintLayout>

    <FrameLayout
        android:id="@+id/hud_fragment_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >

        <FrameLayout
            android:id="@+id/call_fragment_container"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
    </FrameLayout>
</androidx.constraintlayout.widget.ConstraintLayout>