LibreTube/app/src/main/res/xml/audio_player_scene.xml

<?xml version="1.0" encoding="utf-8"?>
<MotionScene xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:motion="http://schemas.android.com/apk/res-auto">

    <Transition
        android:id="@+id/mini_player_transition"
        motion:constraintSetEnd="@+id/end"
        motion:constraintSetStart="@id/start"
        motion:duration="500"
        motion:motionInterpolator="easeInOut">
        <KeyFrameSet>
            <KeyAttribute
                android:alpha="0"
                motion:framePosition="90"
                motion:motionTarget="@+id/miniPlayerControls" />
        </KeyFrameSet>
        <OnClick
            motion:clickAction="toggle"
            motion:duration="500"
            motion:targetId="@+id/miniPlayerControls" />
    </Transition>

    <ConstraintSet android:id="@+id/start">
        <Constraint
            android:id="@+id/audio_player_container"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            motion:layout_constraintBottom_toBottomOf="parent"
            motion:layout_constraintEnd_toEndOf="parent"
            motion:layout_constraintStart_toStartOf="parent"
            motion:layout_constraintTop_toTopOf="parent" />
    </ConstraintSet>

    <ConstraintSet android:id="@+id/end">
        <Constraint
            android:id="@+id/audio_player_container"
            android:layout_width="match_parent"
            android:layout_height="54dp"
            motion:layout_constraintBottom_toBottomOf="parent"
            motion:layout_constraintEnd_toEndOf="parent"
            motion:layout_constraintHorizontal_bias="0.5"
            motion:layout_constraintStart_toStartOf="parent"
            motion:layout_constraintTop_toTopOf="parent"
            motion:layout_constraintVertical_bias="1.0" />
        <Constraint
            android:id="@+id/audio_player_main"
            android:layout_width="0dp"
            android:layout_height="1dp"
            motion:layout_constraintBottom_toBottomOf="parent"
            motion:layout_constraintEnd_toEndOf="parent"
            motion:layout_constraintStart_toStartOf="parent"
            motion:layout_constraintTop_toBottomOf="@+id/main_container" />
        <Constraint
            android:id="@+id/miniPlayerControls"
            android:layout_width="match_parent"
            android:layout_height="54dp"
            android:alpha="1"
            android:paddingEnd="16dp"
            android:visibility="visible"
            motion:layout_constraintBottom_toBottomOf="@+id/audio_player_container"
            motion:layout_constraintEnd_toEndOf="@id/audio_player_container"
            motion:layout_constraintStart_toStartOf="@id/audio_player_container"
            motion:layout_constraintTop_toTopOf="@+id/audio_player_container" />
    </ConstraintSet>
</MotionScene>