Signal-Android/res/layout-v16/video_player.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
             android:orientation="vertical"
             android:layout_width="match_parent"
             android:layout_height="match_parent">

    <com.google.android.exoplayer2.ui.PlayerView
            android:id="@+id/video_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_gravity="center"
            android:gravity="center"/>

</FrameLayout>