allow developers to set the subText of the notifcation

Issue: #5344
PiperOrigin-RevId: 229527963

RELEASENOTES.md

@@ -54,6 +54,8 @@
   ([#5351](https://github.com/google/ExoPlayer/issues/5351)).
 * Fix issue where uneven track durations in MP4 streams can cause OOM problems
   ([#3670](https://github.com/google/ExoPlayer/issues/3670)).
+* Add the sub text to the MediaDescriptionAdapter of the
+  PlayerNotificationManager.
 
 ### 2.9.3 ###
 

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

@@ -127,6 +127,18 @@ public class PlayerNotificationManager {
     String getCurrentContentText(Player player);
 
     /**
+     * Gets the content sub text for the current media item.
+     *
+     * <p>See {@link NotificationCompat.Builder#setSubText(CharSequence)}.
+     *
+     * @param player The {@link Player} for which a notification is being built.
+     */
+    @Nullable
+    default String getCurrentSubText(Player player) {
+      return null;
+    }
+
+    /**
      * Gets the large icon for the current media item.
      *
      * <p>When a bitmap initially needs to be asynchronously loaded, a placeholder (or null) can be
@@ -946,6 +958,7 @@ public class PlayerNotificationManager {
     // Set media specific notification properties from MediaDescriptionAdapter.
     builder.setContentTitle(mediaDescriptionAdapter.getCurrentContentTitle(player));
     builder.setContentText(mediaDescriptionAdapter.getCurrentContentText(player));
+    builder.setSubText(mediaDescriptionAdapter.getCurrentSubText(player));
     if (largeIcon == null) {
       largeIcon =
           mediaDescriptionAdapter.getCurrentLargeIcon(