diff --git a/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadManager.java b/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadManager.java
index 7ad22e000a..8502a56ea7 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadManager.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadManager.java
@@ -173,6 +173,7 @@ public final class DownloadManager {
   private boolean downloadsPaused;
   private int maxParallelDownloads;
   private int minRetryCount;
+  private int notMetRequirements;
   private RequirementsWatcher requirementsWatcher;
 
   /**
@@ -212,7 +213,7 @@ public final class DownloadManager {
     requirementsListener = this::onRequirementsStateChanged;
     requirementsWatcher =
         new RequirementsWatcher(context, requirementsListener, DEFAULT_REQUIREMENTS);
-    int notMetRequirements = requirementsWatcher.start();
+    notMetRequirements = requirementsWatcher.start();
 
     mainHandler = new Handler(Util.getLooper(), this::handleMainMessage);
     HandlerThread internalThread = new HandlerThread("DownloadManager file i/o");
@@ -274,11 +275,21 @@ public final class DownloadManager {
     listeners.remove(listener);
   }
 
-  /** Returns the requirements needed to be met to start downloads. */
+  /** Returns the requirements needed to be met to progress. */
   public Requirements getRequirements() {
     return requirementsWatcher.getRequirements();
   }
 
+  /**
+   * Returns the requirements needed for downloads to progress that are not currently met.
+   *
+   * @return The not met {@link Requirements.RequirementFlags}, or 0 if all requirements are met.
+   */
+  @Requirements.RequirementFlags
+  public int getNotMetRequirements() {
+    return getRequirements().getNotMetRequirements(context);
+  }
+
   /**
    * Sets the requirements that need to be met for downloads to progress.
    *
@@ -413,7 +424,7 @@ public final class DownloadManager {
    * @param request The download request.
    */
   public void addDownload(DownloadRequest request) {
-    addDownload(request, Download.STOP_REASON_NONE);
+    addDownload(request, STOP_REASON_NONE);
   }
 
   /**
@@ -478,6 +489,10 @@ public final class DownloadManager {
     for (Listener listener : listeners) {
       listener.onRequirementsStateChanged(this, requirements, notMetRequirements);
     }
+    if (this.notMetRequirements == notMetRequirements) {
+      return;
+    }
+    this.notMetRequirements = notMetRequirements;
     pendingMessages++;
     internalHandler
         .obtainMessage(MSG_SET_NOT_MET_REQUIREMENTS, notMetRequirements, /* unused */ 0)
@@ -747,10 +762,6 @@ public final class DownloadManager {
     }
 
     private void setNotMetRequirements(@Requirements.RequirementFlags int notMetRequirements) {
-      // TODO: Move this deduplication check to the main thread.
-      if (this.notMetRequirements == notMetRequirements) {
-        return;
-      }
       this.notMetRequirements = notMetRequirements;
       logdFlags("Not met requirements are changed", notMetRequirements);
       for (int i = 0; i < downloadInternals.size(); i++) {
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/offline/WritableDownloadIndex.java b/library/core/src/main/java/com/google/android/exoplayer2/offline/WritableDownloadIndex.java
index 2306363cf5..00b08dc76a 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/offline/WritableDownloadIndex.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/offline/WritableDownloadIndex.java
@@ -17,43 +17,43 @@ package com.google.android.exoplayer2.offline;
 
 import java.io.IOException;
 
-/** An writable index of {@link Download Downloads}. */
+/** A writable index of {@link Download Downloads}. */
 public interface WritableDownloadIndex extends DownloadIndex {
 
   /**
    * Adds or replaces a {@link Download}.
    *
    * @param download The {@link Download} to be added.
-   * @throws throws IOException If an error occurs setting the state.
+   * @throws IOException If an error occurs setting the state.
    */
   void putDownload(Download download) throws IOException;
 
   /**
-   * Removes the {@link Download} with the given {@code id}.
+   * Removes the download with the given ID. Does nothing if a download with the given ID does not
+   * exist.
    *
-   * @param id ID of a {@link Download}.
-   * @throws throws IOException If an error occurs removing the state.
+   * @param id The ID of the download to remove.
+   * @throws IOException If an error occurs removing the state.
    */
   void removeDownload(String id) throws IOException;
+
   /**
    * Sets the stop reason of the downloads in a terminal state ({@link Download#STATE_COMPLETED},
    * {@link Download#STATE_FAILED}).
    *
    * @param stopReason The stop reason.
-   * @throws throws IOException If an error occurs updating the state.
+   * @throws IOException If an error occurs updating the state.
    */
   void setStopReason(int stopReason) throws IOException;
 
   /**
-   * Sets the stop reason of the download with the given {@code id} in a terminal state ({@link
-   * Download#STATE_COMPLETED}, {@link Download#STATE_FAILED}).
+   * Sets the stop reason of the download with the given ID in a terminal state ({@link
+   * Download#STATE_COMPLETED}, {@link Download#STATE_FAILED}). Does nothing if a download with the
+   * given ID does not exist, or if it's not in a terminal state.
    *
-   * <p>If there's no {@link Download} with the given {@code id} or it isn't in a terminal state,
-   * then nothing happens.
-   *
-   * @param id ID of a {@link Download}.
+   * @param id The ID of the download to update.
    * @param stopReason The stop reason.
-   * @throws throws IOException If an error occurs updating the state.
+   * @throws IOException If an error occurs updating the state.
    */
   void setStopReason(String id, int stopReason) throws IOException;
 }