Make javadoc valid html5

As of [JDK-8247957](https://bugs.openjdk.java.net/browse/JDK-8247957), doclint
no longer supports html4.

Tested:
    Some test failures are present, but the CL author has decided to mail the change anyway
PiperOrigin-RevId: 378819179

library/common/src/main/java/com/google/android/exoplayer2/Format.java

@@ -38,7 +38,7 @@ import java.util.List;
  * format being constructed. For information about different types of format, see ExoPlayer's <a
  * href="https://exoplayer.dev/supported-formats.html">Supported formats page</a>.
  *
- * <h3>Fields commonly relevant to all formats</h3>
+ * <h2>Fields commonly relevant to all formats</h2>
  *
  * <ul>
  *   <li>{@link #id}
@@ -52,7 +52,7 @@ import java.util.List;
  *   <li>{@link #metadata}
  * </ul>
  *
- * <h3 id="container-formats">Fields relevant to container formats</h3>
+ * <h2 id="container-formats">Fields relevant to container formats</h2>
  *
  * <ul>
  *   <li>{@link #containerMimeType}
@@ -65,7 +65,7 @@ import java.util.List;
  *       href="#audio-formats">audio</a> and <a href="#text-formats">text</a> formats.
  * </ul>
  *
- * <h3 id="sample-formats">Fields relevant to sample formats</h3>
+ * <h2 id="sample-formats">Fields relevant to sample formats</h2>
  *
  * <ul>
  *   <li>{@link #sampleMimeType}
@@ -78,7 +78,7 @@ import java.util.List;
  *       href="#text-formats">text</a> formats.
  * </ul>
  *
- * <h3 id="video-formats">Fields relevant to video formats</h3>
+ * <h2 id="video-formats">Fields relevant to video formats</h2>
  *
  * <ul>
  *   <li>{@link #width}
@@ -91,7 +91,7 @@ import java.util.List;
  *   <li>{@link #colorInfo}
  * </ul>
  *
- * <h3 id="audio-formats">Fields relevant to audio formats</h3>
+ * <h2 id="audio-formats">Fields relevant to audio formats</h2>
  *
  * <ul>
  *   <li>{@link #channelCount}
@@ -101,7 +101,7 @@ import java.util.List;
  *   <li>{@link #encoderPadding}
  * </ul>
  *
- * <h3 id="text-formats">Fields relevant to text formats</h3>
+ * <h2 id="text-formats">Fields relevant to text formats</h2>
  *
  * <ul>
  *   <li>{@link #accessibilityChannel}

library/common/src/main/java/com/google/android/exoplayer2/Timeline.java

@@ -58,7 +58,7 @@ import java.util.List;
  *
  * <p>The following examples illustrate timelines for various use cases.
  *
- * <h3 id="single-file">Single media file or on-demand stream</h3>
+ * <h2 id="single-file">Single media file or on-demand stream</h2>
  *
  * <p style="align:center"><img src="doc-files/timeline-single-file.svg" alt="Example timeline for a
  * single file">
@@ -68,7 +68,7 @@ import java.util.List;
  * playback. The window's default position is typically at the start of the period (indicated by the
  * black dot in the figure above).
  *
- * <h3>Playlist of media files or on-demand streams</h3>
+ * <h2>Playlist of media files or on-demand streams</h2>
  *
  * <p style="align:center"><img src="doc-files/timeline-playlist.svg" alt="Example timeline for a
  * playlist of files">
@@ -79,7 +79,7 @@ import java.util.List;
  * (e.g. their durations and whether the window is seekable) will often only become known when the
  * player starts buffering the corresponding file or stream.
  *
- * <h3 id="live-limited">Live stream with limited availability</h3>
+ * <h2 id="live-limited">Live stream with limited availability</h2>
  *
  * <p style="align:center"><img src="doc-files/timeline-live-limited.svg" alt="Example timeline for
  * a live stream with limited availability">
@@ -92,7 +92,7 @@ import java.util.List;
  * changes to the live window. Its default position is typically near to the live edge (indicated by
  * the black dot in the figure above).
  *
- * <h3>Live stream with indefinite availability</h3>
+ * <h2>Live stream with indefinite availability</h2>
  *
  * <p style="align:center"><img src="doc-files/timeline-live-indefinite.svg" alt="Example timeline
  * for a live stream with indefinite availability">
@@ -102,7 +102,7 @@ import java.util.List;
  * starts at the beginning of the period to indicate that all of the previously broadcast content
  * can still be played.
  *
- * <h3 id="live-multi-period">Live stream with multiple periods</h3>
+ * <h2 id="live-multi-period">Live stream with multiple periods</h2>
  *
  * <p style="align:center"><img src="doc-files/timeline-live-multi-period.svg" alt="Example timeline
  * for a live stream with multiple periods">
@@ -112,7 +112,7 @@ import java.util.List;
  * limited availability</a> case, except that the window may span more than one period. Multiple
  * periods are also possible in the indefinite availability case.
  *
- * <h3>On-demand stream followed by live stream</h3>
+ * <h2>On-demand stream followed by live stream</h2>
  *
  * <p style="align:center"><img src="doc-files/timeline-advanced.svg" alt="Example timeline for an
  * on-demand stream followed by a live stream">
@@ -122,7 +122,7 @@ import java.util.List;
  * of the on-demand stream ends, playback of the live stream will start from its default position
  * near the live edge.
  *
- * <h3 id="single-file-midrolls">On-demand stream with mid-roll ads</h3>
+ * <h2 id="single-file-midrolls">On-demand stream with mid-roll ads</h2>
  *
  * <p style="align:center"><img src="doc-files/timeline-single-file-midrolls.svg" alt="Example
  * timeline for an on-demand stream with mid-roll ad groups">

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayer.java

@@ -62,7 +62,7 @@ import java.util.List;
  * An extensible media player that plays {@link MediaSource}s. Instances can be obtained from {@link
  * SimpleExoPlayer.Builder}.
  *
- * <h3>Player components</h3>
+ * <h2>Player components</h2>
  *
  * <p>ExoPlayer is designed to make few assumptions about (and hence impose few restrictions on) the
  * type of the media being played, how and where it is stored, and how it is rendered. Rather than
@@ -106,7 +106,7 @@ import java.util.List;
  * {@link DataSource} factories to be injected via their constructors. By providing a custom factory
  * it's possible to load data from a non-standard source, or through a different network stack.
  *
- * <h3>Threading model</h3>
+ * <h2>Threading model</h2>
  *
  * <p>The figure below shows ExoPlayer's threading model.
  *

library/core/src/main/java/com/google/android/exoplayer2/drm/ExoMediaDrm.java

@@ -37,7 +37,7 @@ import java.util.UUID;
 /**
  * Used to obtain keys for decrypting protected media streams.
  *
- * <h3>Reference counting</h3>
+ * <h2>Reference counting</h2>
  *
  * <p>Access to an instance is managed by reference counting, where {@link #acquire()} increments
  * the reference count and {@link #release()} decrements it. When the reference count drops to 0

library/core/src/main/java/com/google/android/exoplayer2/source/DefaultMediaSourceFactory.java

@@ -72,7 +72,7 @@ import java.util.List;
  *       is thrown if none of the available extractors can read the stream.
  * </ul>
  *
- * <h3>Ad support for media items with ad tag URIs</h3>
+ * <h2>Ad support for media items with ad tag URIs</h2>
  *
  * <p>To support media items with {@link MediaItem.PlaybackProperties#adsConfiguration ads
  * configuration}, {@link #setAdsLoaderProvider} and {@link #setAdViewProvider} need to be called to

library/core/src/main/java/com/google/android/exoplayer2/trackselection/DefaultTrackSelector.java

@@ -60,7 +60,7 @@ import org.checkerframework.checker.nullness.qual.EnsuresNonNull;
  * to configurable {@link Parameters}, which can be set by calling {@link
  * #setParameters(Parameters)}.
  *
- * <h3>Modifying parameters</h3>
+ * <h2>Modifying parameters</h2>
  *
  * To modify only some aspects of the parameters currently used by a selector, it's possible to
  * obtain a {@link ParametersBuilder} initialized with the current {@link Parameters}. The desired
@@ -93,7 +93,7 @@ import org.checkerframework.checker.nullness.qual.EnsuresNonNull;
  *
  * Selection {@link Parameters} support many different options, some of which are described below.
  *
- * <h3>Selecting specific tracks</h3>
+ * <h2>Selecting specific tracks</h2>
  *
  * Track selection overrides can be used to select specific tracks. To specify an override for a
  * renderer, it's first necessary to obtain the tracks that have been mapped to it:
@@ -120,7 +120,7 @@ import org.checkerframework.checker.nullness.qual.EnsuresNonNull;
  *         .setSelectionOverride(rendererIndex, rendererTrackGroups, selectionOverride));
  * }</pre>
  *
- * <h3>Constraint based track selection</h3>
+ * <h2>Constraint based track selection</h2>
  *
  * Whilst track selection overrides make it possible to select specific tracks, the recommended way
  * of controlling which tracks are selected is by specifying constraints. For example consider the
@@ -148,14 +148,14 @@ import org.checkerframework.checker.nullness.qual.EnsuresNonNull;
  *       only applied to periods whose tracks match those for which the override was set.
  * </ul>
  *
- * <h3>Disabling renderers</h3>
+ * <h2>Disabling renderers</h2>
  *
  * Renderers can be disabled using {@link ParametersBuilder#setRendererDisabled}. Disabling a
  * renderer differs from setting a {@code null} override because the renderer is disabled
  * unconditionally, whereas a {@code null} override is applied only when the track groups available
  * to the renderer match the {@link TrackGroupArray} for which it was specified.
  *
- * <h3>Tunneling</h3>
+ * <h2>Tunneling</h2>
  *
  * Tunneled playback can be enabled in cases where the combination of renderers and selected tracks
  * support it. Tunneled playback is enabled by passing an audio session ID to {@link

library/core/src/main/java/com/google/android/exoplayer2/trackselection/TrackSelector.java

@@ -32,7 +32,7 @@ import com.google.android.exoplayer2.util.Assertions;
  * the player's {@link Renderer}s. The {@link DefaultTrackSelector} implementation should be
  * suitable for most use cases.
  *
- * <h3>Interactions with the player</h3>
+ * <h2>Interactions with the player</h2>
  *
  * The following interactions occur between the player and its track selector during playback.
  *
@@ -65,7 +65,7 @@ import com.google.android.exoplayer2.util.Assertions;
  *       will call {@link InvalidationListener#onTrackSelectionsInvalidated()}.
  * </ul>
  *
- * <h3>Renderer configuration</h3>
+ * <h2>Renderer configuration</h2>
  *
  * The {@link TrackSelectorResult} returned by {@link #selectTracks(RendererCapabilities[],
  * TrackGroupArray, MediaPeriodId, Timeline)} contains not only {@link TrackSelection}s for each
@@ -77,7 +77,7 @@ import com.google.android.exoplayer2.util.Assertions;
  * configure renderers in a particular way if certain tracks are selected. Hence it makes sense to
  * determine the track selection and corresponding renderer configurations in a single step.
  *
- * <h3>Threading model</h3>
+ * <h2>Threading model</h2>
  *
  * All calls made by the player into the track selector are on the player's internal playback
  * thread. The track selector may call {@link InvalidationListener#onTrackSelectionsInvalidated()}

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/Cache.java

@@ -26,7 +26,7 @@ import java.util.Set;
 /**
  * A cache that supports partial caching of resources.
  *
- * <h3>Terminology</h3>
+ * <h2>Terminology</h2>
  *
  * <ul>
  *   <li>A <em>resource</em> is a complete piece of logical data, for example a complete media file.

library/extractor/src/main/java/com/google/android/exoplayer2/extractor/ExtractorInput.java

@@ -34,7 +34,7 @@ import java.io.InputStream;
  *       wants to read an entire block/frame/header of known length.
  * </ul>
  *
- * <h3>{@link InputStream}-like methods</h3>
+ * <h2>{@link InputStream}-like methods</h2>
  *
  * <p>The {@code read()/peek()} and {@code skip()} methods provide {@link InputStream}-like
  * byte-level access operations. The {@code length} parameter is a maximum, and each method returns
@@ -42,7 +42,7 @@ import java.io.InputStream;
  * the input was reached, or the method was interrupted, or the operation was aborted early for
  * another reason.
  *
- * <h3>Block-based methods</h3>
+ * <h2>Block-based methods</h2>
  *
  * <p>The {@code read/skip/peekFully()} and {@code advancePeekPosition()} methods assume the user
  * wants to read an entire block/frame/header of known length.

library/ui/src/main/java/com/google/android/exoplayer2/ui/DefaultTimeBar.java

@@ -51,7 +51,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
  *
  * <p>A DefaultTimeBar can be customized by setting attributes, as outlined below.
  *
- * <h3>Attributes</h3>
+ * <h2>Attributes</h2>
  *
  * The following attributes can be set on a DefaultTimeBar when used in a layout XML file:
  *

library/ui/src/main/java/com/google/android/exoplayer2/ui/PlayerControlView.java

@@ -66,7 +66,7 @@ import java.util.concurrent.CopyOnWriteArrayList;
  * methods), overriding drawables, overriding the view's layout file, or by specifying a custom view
  * layout file.
  *
- * <h3>Attributes</h3>
+ * <h2>Attributes</h2>
  *
  * The following attributes can be set on a PlayerControlView when used in a layout XML file:
  *
@@ -138,7 +138,7 @@ import java.util.concurrent.CopyOnWriteArrayList;
  *       layout is overridden to specify a custom {@code exo_progress} (see below).
  * </ul>
  *
- * <h3>Overriding drawables</h3>
+ * <h2>Overriding drawables</h2>
  *
  * The drawables used by PlayerControlView (with its default layout file) can be overridden by
  * drawables with the same names defined in your application. The drawables that can be overridden
@@ -162,7 +162,7 @@ import java.util.concurrent.CopyOnWriteArrayList;
  *   <li><b>{@code exo_controls_vr}</b> - The VR icon.
  * </ul>
  *
- * <h3>Overriding the layout file</h3>
+ * <h2>Overriding the layout file</h2>
  *
  * To customize the layout of PlayerControlView throughout your app, or just for certain
  * configurations, you can define {@code exo_player_control_view.xml} layout files in your
@@ -241,7 +241,7 @@ import java.util.concurrent.CopyOnWriteArrayList;
  * <p>All child views are optional and so can be omitted if not required, however where defined they
  * must be of the expected type.
  *
- * <h3>Specifying a custom layout file</h3>
+ * <h2>Specifying a custom layout file</h2>
  *
  * Defining your own {@code exo_player_control_view.xml} is useful to customize the layout of
  * PlayerControlView throughout your application. It's also possible to customize the layout for a

library/ui/src/main/java/com/google/android/exoplayer2/ui/PlayerNotificationManager.java

@@ -75,7 +75,7 @@ import java.util.Map;
  * <p>If the player is released it must be removed from the manager by calling {@code
  * setPlayer(null)}.
  *
- * <h3>Action customization</h3>
+ * <h2>Action customization</h2>
  *
  * Playback actions can be included or omitted as follows:
  *
@@ -140,7 +140,7 @@ import java.util.Map;
  *       </ul>
  * </ul>
  *
- * <h3>Overriding drawables</h3>
+ * <h2>Overriding drawables</h2>
  *
  * The drawables used by PlayerNotificationManager can be overridden by drawables with the same
  * names defined in your application. The drawables that can be overridden are:

library/ui/src/main/java/com/google/android/exoplayer2/ui/PlayerView.java

@@ -83,7 +83,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
  * overriding drawables, overriding the view's layout file, or by specifying a custom view layout
  * file.
  *
- * <h3>Attributes</h3>
+ * <h2>Attributes</h2>
  *
  * The following attributes can be set on a PlayerView when used in a layout XML file:
  *
@@ -175,13 +175,13 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
  *       exo_controller} (see below).
  * </ul>
  *
- * <h3>Overriding drawables</h3>
+ * <h2>Overriding drawables</h2>
  *
  * The drawables used by {@link PlayerControlView} (with its default layout file) can be overridden
  * by drawables with the same names defined in your application. See the {@link PlayerControlView}
  * documentation for a list of drawables that can be overridden.
  *
- * <h3>Overriding the layout file</h3>
+ * <h2>Overriding the layout file</h2>
  *
  * To customize the layout of PlayerView throughout your app, or just for certain configurations,
  * you can define {@code exo_player_view.xml} layout files in your application {@code res/layout*}
@@ -248,7 +248,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
  * <p>All child views are optional and so can be omitted if not required, however where defined they
  * must be of the expected type.
  *
- * <h3>Specifying a custom layout file</h3>
+ * <h2>Specifying a custom layout file</h2>
  *
  * Defining your own {@code exo_player_view.xml} is useful to customize the layout of PlayerView
  * throughout your application. It's also possible to customize the layout for a single instance in

library/ui/src/main/java/com/google/android/exoplayer2/ui/StyledPlayerControlView.java

@@ -88,7 +88,7 @@ import java.util.concurrent.CopyOnWriteArrayList;
  * methods), overriding drawables, overriding the view's layout file, or by specifying a custom view
  * layout file.
  *
- * <h3>Attributes</h3>
+ * <h2>Attributes</h2>
  *
  * The following attributes can be set on a StyledPlayerControlView when used in a layout XML file:
  *
@@ -171,7 +171,7 @@ import java.util.concurrent.CopyOnWriteArrayList;
  *       unless the layout is overridden to specify a custom {@code exo_progress} (see below).
  * </ul>
  *
- * <h3>Overriding drawables</h3>
+ * <h2>Overriding drawables</h2>
  *
  * The drawables used by StyledPlayerControlView (with its default layout file) can be overridden by
  * drawables with the same names defined in your application. The drawables that can be overridden
@@ -196,7 +196,7 @@ import java.util.concurrent.CopyOnWriteArrayList;
  *   <li><b>{@code exo_styled_controls_vr}</b> - The VR icon.
  * </ul>
  *
- * <h3>Overriding the layout file</h3>
+ * <h2>Overriding the layout file</h2>
  *
  * To customize the layout of StyledPlayerControlView throughout your app, or just for certain
  * configurations, you can define {@code exo_styled_player_control_view.xml} layout files in your
@@ -301,7 +301,7 @@ import java.util.concurrent.CopyOnWriteArrayList;
  * <p>All child views are optional and so can be omitted if not required, however where defined they
  * must be of the expected type.
  *
- * <h3 id="CustomLayout">Specifying a custom layout file</h3>
+ * <h2 id="CustomLayout">Specifying a custom layout file</h2>
  *
  * Defining your own {@code exo_styled_player_control_view.xml} is useful to customize the layout of
  * StyledPlayerControlView throughout your application. It's also possible to customize the layout

library/ui/src/main/java/com/google/android/exoplayer2/ui/StyledPlayerView.java

@@ -84,7 +84,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
  * overriding drawables, overriding the view's layout file, or by specifying a custom view layout
  * file.
  *
- * <h3>Attributes</h3>
+ * <h2>Attributes</h2>
  *
  * The following attributes can be set on a StyledPlayerView when used in a layout XML file:
  *
@@ -176,13 +176,13 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
  *       custom {@code exo_controller} (see below).
  * </ul>
  *
- * <h3>Overriding drawables</h3>
+ * <h2>Overriding drawables</h2>
  *
  * The drawables used by {@link StyledPlayerControlView} (with its default layout file) can be
  * overridden by drawables with the same names defined in your application. See the {@link
  * StyledPlayerControlView} documentation for a list of drawables that can be overridden.
  *
- * <h3>Overriding the layout file</h3>
+ * <h2>Overriding the layout file</h2>
  *
  * To customize the layout of StyledPlayerView throughout your app, or just for certain
  * configurations, you can define {@code exo_styled_player_view.xml} layout files in your
@@ -249,7 +249,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
  * <p>All child views are optional and so can be omitted if not required, however where defined they
  * must be of the expected type.
  *
- * <h3>Specifying a custom layout file</h3>
+ * <h2>Specifying a custom layout file</h2>
  *
  * Defining your own {@code exo_styled_player_view.xml} is useful to customize the layout of
  * StyledPlayerView throughout your application. It's also possible to customize the layout for a