packages/SystemUI/res/layout/media_carousel.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2020 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
  -->

<!-- Carousel for media controls -->
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:clipChildren="false"
    android:clipToPadding="false"
    >
    <com.android.systemui.media.MediaScrollView
        android:id="@+id/media_carousel_scroller"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:scrollbars="none"
        android:clipChildren="false"
        android:clipToPadding="false"
        >
        <LinearLayout
            android:id="@+id/media_carousel"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:orientation="horizontal"
            android:clipChildren="false"
            android:clipToPadding="false"
            >
            <!-- QSMediaPlayers will be added here dynamically -->
        </LinearLayout>
    </com.android.systemui.media.MediaScrollView>
    <com.android.systemui.qs.PageIndicator
        android:id="@+id/media_page_indicator"
        android:layout_width="wrap_content"
        android:layout_height="48dp"
        android:layout_marginBottom="4dp"
        android:tint="@color/media_primary_text"
    />
</FrameLayout>