Use Spotify prefetch to load next song before the current one ends.

We still have the problem that each track a new GstPipeline is created and the SpotifyClient creates a new connection to this pipeline.
Therefore playback is not gapless yet.

ext/clementine-spotifyblob/mediapipeline.cpp

@@ -116,7 +116,7 @@ bool MediaPipeline::Init(int sample_rate, int channels) {
 
   // Set size
   byte_rate_ = quint64(sample_rate) * channels * 2;
-  const quint64 bytes = byte_rate_ * length_msec_ / 1000;
+  const quint64 bytes = 2* byte_rate_ * length_msec_ / 1000;
   gst_app_src_set_size(appsrc_, bytes);
 
   // Ready to go

ext/clementine-spotifyblob/spotifyclient.cpp

@@ -300,6 +300,8 @@ void SpotifyClient::MessageArrived(const pb::spotify::Message& message) {
     AddTracksToPlaylist(message.add_tracks_to_playlist());
   } else if (message.has_remove_tracks_from_playlist()) {
     RemoveTracksFromPlaylist(message.remove_tracks_from_playlist());
+  } else if (message.has_prefetch_request()) {
+    PrefetchTrack(message.prefetch_request());
   }
 }
 
@@ -905,20 +907,36 @@ int SpotifyClient::GetDownloadProgress(sp_playlist* playlist) {
 }
 
 void SpotifyClient::StartPlayback(const pb::spotify::PlaybackRequest& req) {
-  // Get a link object from the URI
-  sp_link* link = sp_link_create_from_string(req.track_uri().c_str());
-  if (!link) {
-    SendPlaybackError("Invalid Spotify URI");
-    return;
+  QString uri = QString::fromStdString(req.track_uri());
+
+  sp_link* link;
+  sp_track* track;
+
+  if (prefetched_tracks_.contains(uri)) {
+    PrefetchTrackRequest prefetch_request;
+    prefetch_request = prefetched_tracks_.take(uri);
+    link = prefetch_request.link_;
+    track = prefetch_request.track_;
+
+    qLog(Debug) << "Using prefetched track";
+  } else {
+    // Get a link object from the URI
+    link = sp_link_create_from_string(req.track_uri().c_str());
+    if (!link) {
+      SendPlaybackError("Invalid Spotify URI");
+      return;
+    }
+
+    // Get the track from the link
+    track = sp_link_as_track(link);
+    if (!track) {
+      SendPlaybackError("Spotify URI was not a track");
+      sp_link_release(link);
+      return;
+    }
   }
 
-  // Get the track from the link
-  sp_track* track = sp_link_as_track(link);
-  if (!track) {
-    SendPlaybackError("Spotify URI was not a track");
-    sp_link_release(link);
-    return;
-  }
+  prefetched_tracks_.clear();
 
   PendingPlaybackRequest pending_playback;
   pending_playback.request_ = req;
@@ -967,6 +985,39 @@ void SpotifyClient::TryPlaybackAgain(const PendingPlaybackRequest& req) {
   pending_playback_requests_.removeAll(req);
 }
 
+void SpotifyClient::PrefetchTrack(const pb::spotify::PrefetchRequest &req) {
+  // Get a link object from the URI
+  sp_link* link = sp_link_create_from_string(req.track_uri().c_str());
+  if (!link) {
+    SendPlaybackError("Invalid Spotify URI");
+    return;
+  }
+
+  // Get the track from the link
+  sp_track* track = sp_link_as_track(link);
+  if (!track) {
+    SendPlaybackError("Spotify URI was not a track");
+    sp_link_release(link);
+    return;
+  }
+
+  // Prefetch track
+  sp_error error = sp_session_player_prefetch(session_, track);
+  if (error != SP_ERROR_OK) {
+    qLog(Debug) << sp_error_message(error);
+    return;
+  }
+
+  QString uri = QString::fromStdString(req.track_uri());
+
+  PrefetchTrackRequest prefetch_request;
+  prefetch_request.uri_ = uri;
+  prefetch_request.link_ = link;
+  prefetch_request.track_ = track;
+
+  prefetched_tracks_.insert(uri, prefetch_request);
+}
+
 void SpotifyClient::SendPlaybackError(const QString& error) {
   pb::spotify::Message message;
   pb::spotify::PlaybackError* msg = message.mutable_playback_error();

ext/clementine-spotifyblob/spotifyclient.h

@@ -132,6 +132,7 @@ class SpotifyClient : public AbstractMessageHandler<pb::spotify::Message> {
   void BrowseToplist(const pb::spotify::BrowseToplistRequest& req);
   void SetPlaybackSettings(const pb::spotify::PlaybackSettings& req);
   void SetPaused(const pb::spotify::PauseRequest& req);
+  void PrefetchTrack(const pb::spotify::PrefetchRequest& req);
 
   void SendPlaylistList();
 
@@ -167,6 +168,12 @@ class SpotifyClient : public AbstractMessageHandler<pb::spotify::Message> {
     sp_image* image_;
   };
 
+  struct PrefetchTrackRequest {
+    QString uri_;
+    sp_link* link_;
+    sp_track* track_;
+  };
+
   void TryPlaybackAgain(const PendingPlaybackRequest& req);
   void TryImageAgain(sp_image* image);
   int GetDownloadProgress(sp_playlist* playlist);
@@ -194,6 +201,7 @@ class SpotifyClient : public AbstractMessageHandler<pb::spotify::Message> {
   QMap<sp_albumbrowse*, QString> pending_album_browses_;
   QMap<sp_toplistbrowse*, pb::spotify::BrowseToplistRequest>
       pending_toplist_browses_;
+  QMap<QString, PrefetchTrackRequest> prefetched_tracks_;
 
   QMap<sp_search*, QList<sp_albumbrowse*>> pending_search_album_browses_;
   QMap<sp_albumbrowse*, sp_search*> pending_search_album_browse_responses_;

ext/libclementine-spotifyblob/spotifymessages.proto

@@ -108,6 +108,10 @@ message PlaybackRequest {
   required int32 media_port = 2;
 }
 
+message PrefetchRequest {
+  required string track_uri = 1;
+}
+
 message PlaybackError {
   required string error = 1;
 }
@@ -204,7 +208,7 @@ message RemoveTracksFromPlaylistRequest {
   repeated int64 track_index = 3;
 }
 
-// NEXT_ID: 25
+// NEXT_ID: 26
 message Message {
   // Not currently used
   optional int32 id = 18;
@@ -232,4 +236,5 @@ message Message {
   // ID 22 unused.
   optional AddTracksToPlaylistRequest add_tracks_to_playlist = 23;
   optional RemoveTracksFromPlaylistRequest remove_tracks_from_playlist = 24;
+  optional PrefetchRequest prefetch_request = 25;
 }

src/engines/gstengine.cpp

@@ -332,9 +332,10 @@ void GstEngine::StartPreloading(const QUrl& url, bool force_stop_at_end,
 
   // No crossfading, so we can just queue the new URL in the existing
   // pipeline and get gapless playback (hopefully)
-  if (current_pipeline_)
+  if (current_pipeline_) {
     current_pipeline_->SetNextUrl(gst_url, beginning_nanosec,
                                   force_stop_at_end ? end_nanosec : 0);
+  }
 }
 
 QUrl GstEngine::FixupUrl(const QUrl& url) {
@@ -354,6 +355,8 @@ QUrl GstEngine::FixupUrl(const QUrl& url) {
 bool GstEngine::Load(const QUrl& url, Engine::TrackChangeFlags change,
                      bool force_stop_at_end, quint64 beginning_nanosec,
                      qint64 end_nanosec) {
+  qLog(Debug) << "GstEngine::Load";
+
   EnsureInitialised();
 
   Engine::Base::Load(url, change, force_stop_at_end, beginning_nanosec,
@@ -688,10 +691,10 @@ void GstEngine::EndOfStreamReached(int pipeline_id, bool has_next_track) {
   if (!current_pipeline_.get() || current_pipeline_->id() != pipeline_id)
     return;
 
-  if (!has_next_track) {
+  /*if (!has_next_track) {
     current_pipeline_.reset();
     BufferingFinished();
-  }
+  }*/
   emit TrackEnded();
 }
 

src/engines/gstenginepipeline.cpp

@@ -487,8 +487,8 @@ GstBusSyncReply GstEnginePipeline::BusCallbackSync(GstBus*, GstMessage* msg,
                                                    gpointer self) {
   GstEnginePipeline* instance = reinterpret_cast<GstEnginePipeline*>(self);
 
-  qLog(Debug) << instance->id() << "sync bus message"
-              << GST_MESSAGE_TYPE_NAME(msg);
+  //qLog(Debug) << instance->id() << "sync bus message"
+  //            << GST_MESSAGE_TYPE_NAME(msg);
 
   switch (GST_MESSAGE_TYPE(msg)) {
     case GST_MESSAGE_EOS:
@@ -867,6 +867,8 @@ void GstEnginePipeline::SourceDrainedCallback(GstURIDecodeBin* bin,
                                               gpointer self) {
   GstEnginePipeline* instance = reinterpret_cast<GstEnginePipeline*>(self);
 
+  qDebug() << "SourceDrainedCallback" << instance->has_next_valid_url();
+
   if (instance->has_next_valid_url()) {
     instance->TransitionToNext();
   }
@@ -1155,4 +1157,10 @@ void GstEnginePipeline::SetNextUrl(const QUrl& url, qint64 beginning_nanosec,
   next_url_ = url;
   next_beginning_offset_nanosec_ = beginning_nanosec;
   next_end_offset_nanosec_ = end_nanosec;
+
+  if (url.scheme() == "spotify") {
+    SpotifyService* spotify = InternetModel::Service<SpotifyService>();
+    QMetaObject::invokeMethod(spotify, "SetNextUrl", Qt::QueuedConnection,
+                              Q_ARG(QUrl, url));
+  }
 }

src/internet/spotify/spotifyserver.cpp

@@ -328,3 +328,10 @@ void SpotifyServer::SetPaused(const bool paused) {
   req->set_paused(paused);
   SendOrQueueMessage(message);
 }
+
+void SpotifyServer::PrefetchTrack(const QUrl& url) {
+  pb::spotify::Message message;
+  pb::spotify::PrefetchRequest* req = message.mutable_prefetch_request();
+  req->set_track_uri(DataCommaSizeFromQString(url.toString()));
+  SendOrQueueMessage(message);
+}

src/internet/spotify/spotifyserver.h

@@ -61,6 +61,7 @@ class SpotifyServer : public AbstractMessageHandler<pb::spotify::Message> {
                            bool volume_normalisation);
   void LoadToplist();
   void SetPaused(const bool paused);
+  void PrefetchTrack(const QUrl& url);
 
   int server_port() const;
 

src/internet/spotify/spotifyservice.cpp

@@ -871,6 +871,12 @@ void SpotifyService::SetPaused(bool paused) {
   server_->SetPaused(paused);
 }
 
+void SpotifyService::SetNextUrl(const QUrl &url) {
+  qLog(Debug) << "Next Spotify Url" << url;
+  EnsureServerCreated();
+  server_->PrefetchTrack(url);
+}
+
 void SpotifyService::SyncPlaylistProgress(
     const pb::spotify::SyncPlaylistProgress& progress) {
   qLog(Debug) << "Sync progress:" << progress.sync_progress();

src/internet/spotify/spotifyservice.h

@@ -83,6 +83,7 @@ class SpotifyService : public InternetService {
   void Login(const QString& username, const QString& password);
   Q_INVOKABLE void LoadImage(const QString& id);
   Q_INVOKABLE void SetPaused(bool paused);
+  Q_INVOKABLE void SetNextUrl(const QUrl& url);
 
   SpotifyServer* server() const;