prebuilts/gradle/MediaBrowserService/Application/src/main/res/layout/activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright 2017 The Android Open Source Project
  ~
  ~ Licensed under the Apache License, Version 2.0 (the "License");
  ~ you may not use this file except in compliance with the License.
  ~ You may obtain a copy of the License at
  ~
  ~     http://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing, software
  ~ distributed under the License is distributed on an "AS IS" BASIS,
  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ~ See the License for the specific language governing permissions and
  ~ limitations under the License.
  -->

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
                                             xmlns:app="http://schemas.android.com/apk/res-auto"
                                             xmlns:tools="http://schemas.android.com/tools"
                                             android:id="@+id/frameLayout"
                                             android:layout_width="match_parent"
                                             android:layout_height="match_parent"
                                             tools:background="@drawable/album_jazz_blues">

    <ImageView
        android:id="@+id/album_art"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="fitXY"
        tools:ignore="ContentDescription" />

    <View
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:background="#a0ffffff"
        app:layout_constraintBottom_toBottomOf="@+id/song_artist"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:ignore="ContentDescription" />

    <TextView
        android:id="@+id/song_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="0dp"
        android:gravity="center"
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        app:layout_constraintBottom_toBottomOf="@+id/song_artist"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:text="Song Title" />

    <TextView
        android:id="@+id/song_artist"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:paddingBottom="12dp"
        android:textAppearance="@style/TextAppearance.AppCompat.Medium"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/song_title"
        tools:text="Song Artist" />

    <ImageView
        android:id="@+id/media_controls"
        android:layout_width="192dp"
        android:layout_height="192dp"
        android:alpha=".9"
        android:src="@drawable/ic_play_pause_toggle"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="@+id/guideline"
        tools:ignore="ContentDescription" />

    <Button
        android:id="@+id/button_previous"
        android:layout_width="50dp"
        android:layout_height="0dp"
        android:background="@android:color/transparent"
        android:contentDescription="@string/label_previous"
        android:text=""
        app:layout_constraintBottom_toBottomOf="@+id/media_controls"
        app:layout_constraintStart_toStartOf="@+id/media_controls"
        app:layout_constraintTop_toTopOf="@+id/media_controls" />

    <Button
        android:id="@+id/button_play"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="@android:color/transparent"
        android:contentDescription="@string/label_play_pause"
        android:text=""
        app:layout_constraintBottom_toBottomOf="@+id/media_controls"
        app:layout_constraintEnd_toStartOf="@+id/button_next"
        app:layout_constraintStart_toEndOf="@+id/button_previous"
        app:layout_constraintTop_toTopOf="@+id/media_controls" />

    <Button
        android:id="@+id/button_next"
        android:layout_width="50dp"
        android:layout_height="0dp"
        android:layout_marginStart="8dp"
        android:background="@android:color/transparent"
        android:contentDescription="@string/label_next"
        android:text=""
        app:layout_constraintBottom_toBottomOf="@+id/media_controls"
        app:layout_constraintEnd_toEndOf="@+id/media_controls"
        app:layout_constraintTop_toTopOf="@+id/media_controls" />

    <android.support.constraint.Guideline
        android:id="@+id/guideline"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent=".5" />

    <com.example.android.mediasession.ui.MediaSeekBar
        android:id="@+id/seekbar_audio"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginEnd="16dp"
        android:layout_marginStart="16dp"
        android:paddingBottom="16dp"
        android:paddingTop="16dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent" />

</android.support.constraint.ConstraintLayout>