-Added scroll to fetch for external play queues.

-Modified service player activity scrolling to be instantaneous when difference is too large.
-Modified service player activity to no longer update metadata if nothing change when sync is called.

app/src/main/java/org/schabi/newpipe/player/BackgroundPlayer.java

@@ -378,6 +378,7 @@ public final class BackgroundPlayer extends Service {
 
         @Override
         public void sync(@NonNull final PlayQueueItem item, @Nullable final StreamInfo info) {
+            if (currentItem == item && currentInfo == info) return;
             super.sync(item, info);
 
             resetNotification();

app/src/main/java/org/schabi/newpipe/player/MainVideoPlayer.java

@@ -48,6 +48,7 @@ import com.google.android.exoplayer2.Player;
 import org.schabi.newpipe.R;
 import org.schabi.newpipe.extractor.stream.StreamInfo;
 import org.schabi.newpipe.extractor.stream.VideoStream;
+import org.schabi.newpipe.fragments.OnScrollBelowItemsListener;
 import org.schabi.newpipe.player.helper.PlayerHelper;
 import org.schabi.newpipe.playlist.PlayQueueItem;
 import org.schabi.newpipe.playlist.PlayQueueItemBuilder;
@@ -397,7 +398,7 @@ public final class MainVideoPlayer extends Activity {
             getControlsRoot().setVisibility(View.INVISIBLE);
             queueLayout.setVisibility(View.VISIBLE);
 
-            itemsList.smoothScrollToPosition(playQueue.getIndex());
+            itemsList.scrollToPosition(playQueue.getIndex());
         }
 
         private void onQueueClosed() {
@@ -565,6 +566,9 @@ public final class MainVideoPlayer extends Activity {
             itemsList.setClickable(true);
             itemsList.setLongClickable(true);
 
+            itemsList.clearOnScrollListeners();
+            itemsList.addOnScrollListener(getQueueScrollListener());
+
             itemTouchHelper = new ItemTouchHelper(getItemTouchCallback());
             itemTouchHelper.attachToRecyclerView(itemsList);
 
@@ -578,6 +582,19 @@ public final class MainVideoPlayer extends Activity {
             });
         }
 
+        private OnScrollBelowItemsListener getQueueScrollListener() {
+            return new OnScrollBelowItemsListener() {
+                @Override
+                public void onScrolledDown(RecyclerView recyclerView) {
+                    if (playQueue != null && !playQueue.isComplete()) {
+                        playQueue.fetch();
+                    } else if (itemsList != null) {
+                        itemsList.clearOnScrollListeners();
+                    }
+                }
+            };
+        }
+
         private ItemTouchHelper.SimpleCallback getItemTouchCallback() {
             return new ItemTouchHelper.SimpleCallback(ItemTouchHelper.UP | ItemTouchHelper.DOWN, 0) {
                 @Override

app/src/main/java/org/schabi/newpipe/player/PopupVideoPlayer.java

@@ -573,6 +573,7 @@ public final class PopupVideoPlayer extends Service {
 
         @Override
         public void sync(@NonNull PlayQueueItem item, @Nullable StreamInfo info) {
+            if (currentItem == item && currentInfo == info) return;
             super.sync(item, info);
             updateMetadata();
         }

app/src/main/java/org/schabi/newpipe/player/ServicePlayerActivity.java

@@ -28,6 +28,7 @@ import com.google.android.exoplayer2.Player;
 
 import org.schabi.newpipe.R;
 import org.schabi.newpipe.extractor.stream.StreamInfo;
+import org.schabi.newpipe.fragments.OnScrollBelowItemsListener;
 import org.schabi.newpipe.player.event.PlayerEventListener;
 import org.schabi.newpipe.playlist.PlayQueueItem;
 import org.schabi.newpipe.playlist.PlayQueueItemBuilder;
@@ -57,6 +58,8 @@ public abstract class ServicePlayerActivity extends AppCompatActivity
     private static final int PLAYBACK_SPEED_POPUP_MENU_GROUP_ID = 61;
     private static final int PLAYBACK_PITCH_POPUP_MENU_GROUP_ID = 97;
 
+    private static final int SMOOTH_SCROLL_MAXIMUM_DISTANCE = 80;
+
     private View rootView;
 
     private RecyclerView itemsList;
@@ -225,6 +228,8 @@ public abstract class ServicePlayerActivity extends AppCompatActivity
         itemsList.setAdapter(player.getPlayQueueAdapter());
         itemsList.setClickable(true);
         itemsList.setLongClickable(true);
+        itemsList.clearOnScrollListeners();
+        itemsList.addOnScrollListener(getQueueScrollListener());
 
         itemTouchHelper = new ItemTouchHelper(getItemTouchCallback());
         itemTouchHelper.attachToRecyclerView(itemsList);
@@ -345,6 +350,19 @@ public abstract class ServicePlayerActivity extends AppCompatActivity
     // Component Helpers
     ////////////////////////////////////////////////////////////////////////////
 
+    private OnScrollBelowItemsListener getQueueScrollListener() {
+        return new OnScrollBelowItemsListener() {
+            @Override
+            public void onScrolledDown(RecyclerView recyclerView) {
+                if (player != null && player.getPlayQueue() != null && !player.getPlayQueue().isComplete()) {
+                    player.getPlayQueue().fetch();
+                } else if (itemsList != null) {
+                    itemsList.clearOnScrollListeners();
+                }
+            }
+        };
+    }
+
     private ItemTouchHelper.SimpleCallback getItemTouchCallback() {
         return new ItemTouchHelper.SimpleCallback(ItemTouchHelper.UP | ItemTouchHelper.DOWN, 0) {
             @Override
@@ -401,7 +419,23 @@ public abstract class ServicePlayerActivity extends AppCompatActivity
     }
 
     private void scrollToSelected() {
-        itemsList.smoothScrollToPosition(player.getPlayQueue().getIndex());
+        if (player == null) return;
+
+        final int currentPlayingIndex = player.getPlayQueue().getIndex();
+        final int currentVisibleIndex;
+        if (itemsList.getLayoutManager() instanceof LinearLayoutManager) {
+            final LinearLayoutManager layout = ((LinearLayoutManager) itemsList.getLayoutManager());
+            currentVisibleIndex = layout.findFirstVisibleItemPosition();
+        } else {
+            currentVisibleIndex = 0;
+        }
+
+        final int distance = Math.abs(currentPlayingIndex - currentVisibleIndex);
+        if (distance < SMOOTH_SCROLL_MAXIMUM_DISTANCE) {
+            itemsList.smoothScrollToPosition(currentPlayingIndex);
+        } else {
+            itemsList.scrollToPosition(currentPlayingIndex);
+        }
     }
 
     ////////////////////////////////////////////////////////////////////////////