diff --git a/library/core/src/main/java/com/google/android/exoplayer2/source/TrackGroup.java b/library/common/src/main/java/com/google/android/exoplayer2/source/TrackGroup.java
similarity index 86%
rename from library/core/src/main/java/com/google/android/exoplayer2/source/TrackGroup.java
rename to library/common/src/main/java/com/google/android/exoplayer2/source/TrackGroup.java
index 9e837bf05d..607f797103 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/source/TrackGroup.java
+++ b/library/common/src/main/java/com/google/android/exoplayer2/source/TrackGroup.java
@@ -23,20 +23,10 @@ import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.util.Assertions;
 import java.util.Arrays;
 
-// TODO: Add an allowMultipleStreams boolean to indicate where the one stream per group restriction
-// does not apply.
-/**
- * Defines a group of tracks exposed by a {@link MediaPeriod}.
- *
- * <p>A {@link MediaPeriod} is only able to provide one {@link SampleStream} corresponding to a
- * group at any given time, however this {@link SampleStream} may adapt between multiple tracks
- * within the group.
- */
+/** Defines an immutable group of tracks identified by their format identity. */
 public final class TrackGroup implements Parcelable {
 
-  /**
-   * The number of tracks in the group.
-   */
+  /** The number of tracks in the group. */
   public final int length;
 
   private final Format[] formats;
@@ -45,7 +35,7 @@ public final class TrackGroup implements Parcelable {
   private int hashCode;
 
   /**
-   * @param formats The track formats. Must not be null, contain null elements or be of length 0.
+   * @param formats The track formats. At least one {@link Format} must be provided.
    */
   public TrackGroup(Format... formats) {
     Assertions.checkState(formats.length > 0);
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/source/TrackGroupArray.java b/library/common/src/main/java/com/google/android/exoplayer2/source/TrackGroupArray.java
similarity index 90%
rename from library/core/src/main/java/com/google/android/exoplayer2/source/TrackGroupArray.java
rename to library/common/src/main/java/com/google/android/exoplayer2/source/TrackGroupArray.java
index e737a5fafa..8db7b9c385 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/source/TrackGroupArray.java
+++ b/library/common/src/main/java/com/google/android/exoplayer2/source/TrackGroupArray.java
@@ -21,17 +21,13 @@ import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.C;
 import java.util.Arrays;
 
-/** An array of {@link TrackGroup}s exposed by a {@link MediaPeriod}. */
+/** An immutable array of {@link TrackGroup}s. */
 public final class TrackGroupArray implements Parcelable {
 
-  /**
-   * The empty array.
-   */
+  /** The empty array. */
   public static final TrackGroupArray EMPTY = new TrackGroupArray();
 
-  /**
-   * The number of groups in the array. Greater than or equal to zero.
-   */
+  /** The number of groups in the array. Greater than or equal to zero. */
   public final int length;
 
   private final TrackGroup[] trackGroups;
@@ -39,9 +35,7 @@ public final class TrackGroupArray implements Parcelable {
   // Lazily initialized hashcode.
   private int hashCode;
 
-  /**
-   * @param trackGroups The groups. Must not be null or contain null elements, but may be empty.
-   */
+  /** @param trackGroups The groups. May be empty. */
   public TrackGroupArray(TrackGroup... trackGroups) {
     this.trackGroups = trackGroups;
     this.length = trackGroups.length;
@@ -83,9 +77,7 @@ public final class TrackGroupArray implements Parcelable {
     return C.INDEX_UNSET;
   }
 
-  /**
-   * Returns whether this track group array is empty.
-   */
+  /** Returns whether this track group array is empty. */
   public boolean isEmpty() {
     return length == 0;
   }
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/source/MediaPeriod.java b/library/core/src/main/java/com/google/android/exoplayer2/source/MediaPeriod.java
index 39b207e264..1c5a23e48c 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/source/MediaPeriod.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/source/MediaPeriod.java
@@ -29,14 +29,16 @@ import org.checkerframework.checker.nullness.compatqual.NullableType;
 
 /**
  * Loads media corresponding to a {@link Timeline.Period}, and allows that media to be read. All
- * methods are called on the player's internal playback thread, as described in the
- * {@link ExoPlayer} Javadoc.
+ * methods are called on the player's internal playback thread, as described in the {@link
+ * ExoPlayer} Javadoc.
+ *
+ * <p>A {@link MediaPeriod} may only able to provide one {@link SampleStream} corresponding to a
+ * group at any given time, however this {@link SampleStream} may adapt between multiple tracks
+ * within the group.
  */
 public interface MediaPeriod extends SequenceableLoader {
 
-  /**
-   * A callback to be notified of {@link MediaPeriod} events.
-   */
+  /** A callback to be notified of {@link MediaPeriod} events. */
   interface Callback extends SequenceableLoader.Callback<MediaPeriod> {
 
     /**