-Baked stream info resolution into custom media source, allowing for simpler playlist control.

-Added track merging on different stream qualities, allowing for implementation of smooth transition on A/V quality and captions change.

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

@@ -37,6 +37,7 @@ import android.widget.RemoteViews;
 
 import com.google.android.exoplayer2.Player;
 import com.google.android.exoplayer2.source.MediaSource;
+import com.google.android.exoplayer2.source.MergingMediaSource;
 
 import org.schabi.newpipe.BuildConfig;
 import org.schabi.newpipe.MainActivity;
@@ -49,6 +50,9 @@ import org.schabi.newpipe.util.Constants;
 import org.schabi.newpipe.util.ListHelper;
 import org.schabi.newpipe.util.ThemeHelper;
 
+import java.util.ArrayList;
+import java.util.List;
+
 
 /**
  * Base players joining the common properties
@@ -390,9 +394,14 @@ public final class BackgroundPlayer extends Service {
         }
 
         @Override
-        public MediaSource sourceOf(final StreamInfo info, final int sortedStreamsIndex) {
+        public MediaSource sourceOf(final StreamInfo info) {
-            final AudioStream audio = ListHelper.getHighestQualityAudio(info.audio_streams);
+            List<MediaSource> sources = new ArrayList<>();
-            return buildMediaSource(audio.url, MediaFormat.getSuffixById(audio.format));
+            for (final AudioStream audio : info.audio_streams) {
+                final MediaSource audioSource = buildMediaSource(audio.url, MediaFormat.getSuffixById(audio.format));
+                sources.add(audioSource);
+            }
+
+            return new MergingMediaSource(sources.toArray(new MediaSource[sources.size()]));
         }
 
         @Override

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

@@ -72,8 +72,8 @@ import org.schabi.newpipe.R;
 import org.schabi.newpipe.extractor.InfoItem;
 import org.schabi.newpipe.extractor.stream.StreamInfo;
 import org.schabi.newpipe.extractor.stream.StreamInfoItem;
+import org.schabi.newpipe.player.playback.MediaSourceManager;
 import org.schabi.newpipe.player.playback.PlaybackListener;
-import org.schabi.newpipe.player.playback.PlaybackManager;
 import org.schabi.newpipe.playlist.ExternalPlayQueue;
 import org.schabi.newpipe.playlist.PlayQueue;
 import org.schabi.newpipe.playlist.PlayQueueItem;
@@ -139,7 +139,7 @@ public abstract class BasePlayer implements Player.EventListener,
     // Playback
     //////////////////////////////////////////////////////////////////////////*/
 
-    protected PlaybackManager playbackManager;
+    protected MediaSourceManager playbackManager;
     protected PlayQueue playQueue;
 
     private boolean isRecovery = false;
@@ -158,7 +158,6 @@ public abstract class BasePlayer implements Player.EventListener,
 
     protected SimpleExoPlayer simpleExoPlayer;
     protected boolean isPrepared = false;
-    protected boolean wasPlaying = false;
 
     protected CacheDataSourceFactory cacheDataSourceFactory;
     protected final DefaultExtractorsFactory extractorsFactory = new DefaultExtractorsFactory();
@@ -297,7 +296,7 @@ public abstract class BasePlayer implements Player.EventListener,
 
         playQueue = queue;
         playQueue.init();
-        playbackManager = new PlaybackManager(this, playQueue);
+        playbackManager = new MediaSourceManager(this, playQueue);
     }
 
     public void initThumbnail(final String url) {
@@ -442,14 +441,12 @@ public abstract class BasePlayer implements Player.EventListener,
 
         if (isResumeAfterAudioFocusGain()) {
             simpleExoPlayer.setPlayWhenReady(true);
-            wasPlaying = true;
         }
     }
 
     protected void onAudioFocusLoss() {
         if (DEBUG) Log.d(TAG, "onAudioFocusLoss() called");
         simpleExoPlayer.setPlayWhenReady(false);
-        wasPlaying = false;
     }
 
     protected void onAudioFocusLossCanDuck() {
@@ -586,7 +583,7 @@ public abstract class BasePlayer implements Player.EventListener,
         }
 
         // Good to go...
-        simpleExoPlayer.setPlayWhenReady(wasPlaying);
+        simpleExoPlayer.setPlayWhenReady(true);
     }
 
     /*//////////////////////////////////////////////////////////////////////////
@@ -669,11 +666,10 @@ public abstract class BasePlayer implements Player.EventListener,
         if (DEBUG) Log.d(TAG, "onPositionDiscontinuity() called with: " +
                 "window index = [" + newWindowIndex + "], queue index = [" + newQueueIndex + "]");
 
-        if (newQueueIndex == -1) {
+        // If the user selects a new track, then the discontinuity occurs after the index is changed.
-            playQueue.offsetIndex(+1);
+        // Therefore, the only source that causes a discrepancy would be autoplay,
-        } else {
+        // which can only offset the current track by +1.
-            playQueue.setIndex(newQueueIndex);
+        if (newQueueIndex != playQueue.getIndex()) playQueue.offsetIndex(+1);
-        }
     }
 
     @Override
@@ -690,31 +686,20 @@ public abstract class BasePlayer implements Player.EventListener,
         if (simpleExoPlayer == null) return;
         if (DEBUG) Log.d(TAG, "Blocking...");
 
-        simpleExoPlayer.removeListener(this);
-        changeState(STATE_BLOCKED);
-
-        wasPlaying = simpleExoPlayer.getPlayWhenReady();
-        simpleExoPlayer.setPlayWhenReady(false);
-    }
-
-    @Override
-    public void prepare(final MediaSource mediaSource) {
-        if (simpleExoPlayer == null) return;
-        if (DEBUG) Log.d(TAG, "Preparing...");
-
         simpleExoPlayer.stop();
         isPrepared = false;
 
-        simpleExoPlayer.prepare(mediaSource);
+        changeState(STATE_BLOCKED);
     }
 
     @Override
-    public void unblock() {
+    public void unblock(final MediaSource mediaSource) {
         if (simpleExoPlayer == null) return;
         if (DEBUG) Log.d(TAG, "Unblocking...");
 
         if (getCurrentState() == STATE_BLOCKED) changeState(STATE_BUFFERING);
-        simpleExoPlayer.addListener(this);
+
+        simpleExoPlayer.prepare(mediaSource);
     }
 
     @Override
@@ -762,7 +747,6 @@ public abstract class BasePlayer implements Player.EventListener,
             else playQueue.setIndex(0);
         }
         simpleExoPlayer.setPlayWhenReady(!isPlaying());
-        wasPlaying = simpleExoPlayer.getPlayWhenReady();
     }
 
     public void onFastRewind() {

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

@@ -63,7 +63,7 @@ import org.schabi.newpipe.extractor.exceptions.ReCaptchaException;
 import org.schabi.newpipe.extractor.services.youtube.YoutubeStreamExtractor;
 import org.schabi.newpipe.extractor.stream.StreamInfo;
 import org.schabi.newpipe.player.old.PlayVideoActivity;
-import org.schabi.newpipe.player.playback.PlaybackManager;
+import org.schabi.newpipe.player.playback.MediaSourceManager;
 import org.schabi.newpipe.playlist.PlayQueueItem;
 import org.schabi.newpipe.playlist.SinglePlayQueue;
 import org.schabi.newpipe.report.ErrorActivity;
@@ -743,7 +743,7 @@ public final class PopupVideoPlayer extends Service {
                 public void run() {
                     playerImpl.playQueue = new SinglePlayQueue(info, PlayQueueItem.DEFAULT_QUALITY);
                     playerImpl.playQueue.init();
-                    playerImpl.playbackManager = new PlaybackManager(playerImpl, playerImpl.playQueue);
+                    playerImpl.playbackManager = new MediaSourceManager(playerImpl, playerImpl.playQueue);
                 }
             });
         }

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

@@ -57,7 +57,6 @@ import org.schabi.newpipe.extractor.MediaFormat;
 import org.schabi.newpipe.extractor.stream.AudioStream;
 import org.schabi.newpipe.extractor.stream.StreamInfo;
 import org.schabi.newpipe.extractor.stream.VideoStream;
-import org.schabi.newpipe.player.playback.PlaybackManager;
 import org.schabi.newpipe.playlist.PlayQueue;
 import org.schabi.newpipe.playlist.PlayQueueItem;
 import org.schabi.newpipe.playlist.SinglePlayQueue;
@@ -104,6 +103,7 @@ public abstract class VideoPlayer extends BasePlayer implements SimpleExoPlayer.
     private static final float[] PLAYBACK_SPEEDS = {0.5f, 0.75f, 1f, 1.25f, 1.5f, 1.75f, 2f};
 
     private boolean startedFromNewPipe = true;
+    protected boolean wasPlaying = false;
 
     /*//////////////////////////////////////////////////////////////////////////
     // Views
@@ -255,24 +255,21 @@ public abstract class VideoPlayer extends BasePlayer implements SimpleExoPlayer.
         buildPlaybackSpeedMenu(playbackSpeedPopupMenu);
     }
 
-    @Override
+    public MediaSource sourceOf(final StreamInfo info) {
-    public MediaSource sourceOf(final StreamInfo info, final int sortedStreamsIndex) {
         final List<VideoStream> videos = ListHelper.getSortedStreamVideosList(context, info.video_streams, info.video_only_streams, false);
+        List<MediaSource> sources = new ArrayList<>();
 
-        final VideoStream video;
+        for (final VideoStream video : videos) {
-        if (sortedStreamsIndex == PlayQueueItem.DEFAULT_QUALITY) {
-            final int index = ListHelper.getDefaultResolutionIndex(context, videos);
-            video = videos.get(index);
-        } else {
-            video = videos.get(sortedStreamsIndex);
-        }
-
             final MediaSource mediaSource = buildMediaSource(video.url, MediaFormat.getSuffixById(video.format));
-        if (!video.isVideoOnly) return mediaSource;
+            sources.add(mediaSource);
+        }
 
         final AudioStream audio = ListHelper.getHighestQualityAudio(info.audio_streams);
         final Uri audioUri = Uri.parse(audio.url);
-        return new MergingMediaSource(mediaSource, new ExtractorMediaSource(audioUri, cacheDataSourceFactory, extractorsFactory, null, null));
+        final MediaSource audioSource = new ExtractorMediaSource(audioUri, cacheDataSourceFactory, extractorsFactory, null, null);
+        sources.add(audioSource);
+
+        return new MergingMediaSource(sources.toArray(new MediaSource[sources.size()]));
     }
 
     public void buildQualityMenu(PopupMenu popupMenu) {

app/src/main/java/org/schabi/newpipe/player/mediasource/DeferredMediaSource.java

@@ -0,0 +1,82 @@
+package org.schabi.newpipe.player.mediasource;
+
+import android.os.Looper;
+
+import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.ExoPlayer;
+import com.google.android.exoplayer2.source.MediaPeriod;
+import com.google.android.exoplayer2.source.MediaSource;
+import com.google.android.exoplayer2.source.MergingMediaSource;
+import com.google.android.exoplayer2.source.SinglePeriodTimeline;
+import com.google.android.exoplayer2.upstream.Allocator;
+
+import org.schabi.newpipe.extractor.stream.StreamInfo;
+import org.schabi.newpipe.playlist.PlayQueueItem;
+
+import java.io.IOException;
+import java.util.List;
+
+public final class DeferredMediaSource implements MediaSource {
+
+    public interface Callback {
+        MediaSource sourceOf(final StreamInfo info);
+    }
+
+    final private PlayQueueItem stream;
+    final private Callback callback;
+
+    private StreamInfo info;
+    private MediaSource mediaSource;
+
+    private ExoPlayer exoPlayer;
+    private boolean isTopLevel;
+    private Listener listener;
+
+    public DeferredMediaSource(final PlayQueueItem stream, final Callback callback) {
+        this.stream = stream;
+        this.callback = callback;
+    }
+
+    @Override
+    public void prepareSource(ExoPlayer exoPlayer, boolean isTopLevelSource, Listener listener) {
+        this.exoPlayer = exoPlayer;
+        this.isTopLevel = isTopLevelSource;
+        this.listener = listener;
+
+        listener.onSourceInfoRefreshed(new SinglePeriodTimeline(C.TIME_UNSET, false), null);
+    }
+
+    @Override
+    public void maybeThrowSourceInfoRefreshError() throws IOException {
+        if (mediaSource != null) {
+            mediaSource.maybeThrowSourceInfoRefreshError();
+        }
+    }
+
+    @Override
+    public MediaPeriod createPeriod(MediaPeriodId mediaPeriodId, Allocator allocator) {
+        // This must be called on a non-main thread
+        if (Looper.myLooper() == Looper.getMainLooper()) {
+            throw new UnsupportedOperationException("Source preparation is blocking, it must be run on non-UI thread.");
+        }
+
+        info = stream.getStream().blockingGet();
+
+        mediaSource = callback.sourceOf(info);
+        mediaSource.prepareSource(exoPlayer, isTopLevel, listener);
+
+        return mediaSource.createPeriod(mediaPeriodId, allocator);
+    }
+
+    @Override
+    public void releasePeriod(MediaPeriod mediaPeriod) {
+        mediaSource.releasePeriod(mediaPeriod);
+    }
+
+    @Override
+    public void releaseSource() {
+        if (mediaSource != null) mediaSource.releaseSource();
+        info = null;
+        mediaSource = null;
+    }
+}

app/src/main/java/org/schabi/newpipe/player/playback/MediaSourceManager.java

@@ -8,6 +8,7 @@ import com.google.android.exoplayer2.source.MediaSource;
 import org.reactivestreams.Subscriber;
 import org.reactivestreams.Subscription;
 import org.schabi.newpipe.extractor.stream.StreamInfo;
+import org.schabi.newpipe.player.mediasource.DeferredMediaSource;
 import org.schabi.newpipe.playlist.PlayQueue;
 import org.schabi.newpipe.playlist.PlayQueueItem;
 import org.schabi.newpipe.playlist.events.PlayQueueMessage;
@@ -25,12 +26,12 @@ import io.reactivex.disposables.CompositeDisposable;
 import io.reactivex.disposables.Disposable;
 import io.reactivex.functions.Consumer;
 
-public class PlaybackManager {
+public class MediaSourceManager implements DeferredMediaSource.Callback {
-    private final String TAG = "PlaybackManager@" + Integer.toHexString(hashCode());
+    private final String TAG = "MediaSourceManager@" + Integer.toHexString(hashCode());
     // One-side rolling window size for default loading
-    // Effectively loads WINDOW_SIZE * 2 + 1 streams, should be at least 1
+    // Effectively loads WINDOW_SIZE * 2 + 1 streams, should be at least 1 to ensure gapless playback
     // todo: inject this parameter, allow user settings perhaps
-    private static final int WINDOW_SIZE = 3;
+    private static final int WINDOW_SIZE = 1;
 
     private final PlaybackListener playbackListener;
     private final PlayQueue playQueue;
@@ -46,9 +47,8 @@ public class PlaybackManager {
     private CompositeDisposable disposables;
 
     private boolean isBlocked;
-    private boolean hasReset;
 
-    public PlaybackManager(@NonNull final PlaybackListener listener,
+    public MediaSourceManager(@NonNull final PlaybackListener listener,
                               @NonNull final PlayQueue playQueue) {
         this.playbackListener = listener;
         this.playQueue = playQueue;
@@ -114,22 +114,27 @@ public class PlaybackManager {
             public void onNext(@NonNull PlayQueueMessage event) {
                 // why no pattern matching in Java =(
                 switch (event.type()) {
-                    case INIT:
-                        tryBlock();
-                        resetSources();
-                        break;
                     case APPEND:
                         break;
                     case SELECT:
                         if (isBlocked) break;
-                        if (isCurrentIndexLoaded()) sync(); else tryBlock();
+                        if (isCurrentIndexLoaded()) {
+                            sync();
+                        } else {
+                            tryBlock();
+                            resetSources();
+                        }
                         break;
                     case REMOVE:
                         final RemoveEvent removeEvent = (RemoveEvent) event;
                         if (!removeEvent.isCurrent()) {
                             remove(removeEvent.index());
-                            break;
+                        } else {
+                            tryBlock();
+                            resetSources();
                         }
+                        break;
+                    case INIT:
                     case UPDATE:
                     case REORDER:
                         tryBlock();
@@ -182,13 +187,8 @@ public class PlaybackManager {
 
     private boolean tryUnblock() {
         if (isPlayQueueReady() && isCurrentIndexLoaded() && isBlocked) {
-            if (hasReset) {
-                playbackListener.prepare(sources);
-                hasReset = false;
-            }
-
             isBlocked = false;
-            playbackListener.unblock();
+            playbackListener.unblock(sources);
             return true;
         }
         return false;
@@ -208,53 +208,10 @@ public class PlaybackManager {
     }
 
     private void load() {
-        // The current item has higher priority
+        for (final PlayQueueItem item : playQueue.getStreams()) {
-        final int currentIndex = playQueue.getIndex();
+            insert(playQueue.indexOf(item), new DeferredMediaSource(item, this));
-        final PlayQueueItem currentItem = playQueue.get(currentIndex);
-        if (currentItem == null) return;
-        load(currentItem);
-
-        // Load boundaries to ensure correct looping
-        if (sourceToQueueIndex.indexOf(0) == -1) load(playQueue.get(0));
-        if (sourceToQueueIndex.indexOf(playQueue.size() - 1) == -1) load(playQueue.get(playQueue.size() - 1));
-
-        // The rest are just for seamless playback
-        final int leftBound = Math.max(0, currentIndex - WINDOW_SIZE);
-        final int rightBound = Math.min(playQueue.size(), currentIndex + WINDOW_SIZE + 1);
-        final List<PlayQueueItem> items = new ArrayList<>(playQueue.getStreams().subList(leftBound, rightBound));
-
-        for (final PlayQueueItem item: items) load(item);
-    }
-
-    private void load(@Nullable final PlayQueueItem item) {
-        if (item == null) return;
-
-        item.getStream().subscribe(new SingleObserver<StreamInfo>() {
-            @Override
-            public void onSubscribe(@NonNull Disposable d) {
-                if (disposables == null) {
-                    d.dispose();
-                    return;
-                }
-
-                disposables.add(d);
-            }
-
-            @Override
-            public void onSuccess(@NonNull StreamInfo streamInfo) {
-                final MediaSource source = playbackListener.sourceOf(streamInfo, item.getSortedQualityIndex());
-                final int itemIndex = playQueue.indexOf(item);
-                // replace all except the currently playing
-                insert(itemIndex, source, itemIndex != playQueue.getIndex());
             if (tryUnblock()) sync();
         }
-
-            @Override
-            public void onError(@NonNull Throwable e) {
-                playQueue.remove(playQueue.indexOf(item));
-                load();
-            }
-        });
     }
 
     private void resetSources() {
@@ -263,7 +220,6 @@ public class PlaybackManager {
         if (this.sourceToQueueIndex != null) this.sourceToQueueIndex.clear();
 
         this.sources = new DynamicConcatenatingMediaSource();
-        this.hasReset = true;
     }
 
     /*//////////////////////////////////////////////////////////////////////////
@@ -272,7 +228,7 @@ public class PlaybackManager {
 
     // Insert source into playlist with position in respect to the play queue
     // If the play queue index already exists, then the insert is ignored
-    private void insert(final int queueIndex, final MediaSource source, final boolean replace) {
+    private void insert(final int queueIndex, final MediaSource source) {
         if (queueIndex < 0) return;
 
         int pos = Collections.binarySearch(sourceToQueueIndex, queueIndex);
@@ -280,9 +236,6 @@ public class PlaybackManager {
             final int sourceIndex = -pos-1;
             sourceToQueueIndex.add(sourceIndex, queueIndex);
             sources.addMediaSource(sourceIndex, source);
-        } else if (replace) {
-            sources.addMediaSource(pos + 1, source);
-            sources.removeMediaSource(pos);
         }
     }
 
@@ -300,4 +253,9 @@ public class PlaybackManager {
             sourceToQueueIndex.set(i, sourceToQueueIndex.get(i) - 1);
         }
     }
+
+    @Override
+    public MediaSource sourceOf(StreamInfo info) {
+        return playbackListener.sourceOf(info);
+    }
 }

app/src/main/java/org/schabi/newpipe/player/playback/PlaybackListener.java

@@ -4,6 +4,8 @@ import com.google.android.exoplayer2.source.MediaSource;
 
 import org.schabi.newpipe.extractor.stream.StreamInfo;
 
+import java.util.List;
+
 public interface PlaybackListener {
     /*
     * Called when the stream at the current queue index is not ready yet.
@@ -13,23 +15,13 @@ public interface PlaybackListener {
     * */
     void block();
 
-
-    /*
-    * Called when the media source is rebuilt.
-    * Signals to the listener to prepare the media source again.
-    * The provided media source is always non-empty.
-    *
-    * May be called only after blocking and before unblocking.
-    * */
-    void prepare(final MediaSource mediaSource);
-
     /*
     * Called when the stream at the current queue index is ready.
     * Signals to the listener to resume the player.
     *
     * May be called only when the player is blocked.
     * */
-    void unblock();
+    void unblock(final MediaSource mediaSource);
 
     /*
     * Called when the queue index is refreshed.
@@ -46,7 +38,7 @@ public interface PlaybackListener {
     *
     * May be called at any time.
     * */
-    MediaSource sourceOf(final StreamInfo info, final int sortedStreamsIndex);
+    MediaSource sourceOf(final StreamInfo info);
 
     /*
     * Called when the play queue can no longer to played or used.