Add song fingerprinting and tracking

Fixes #296

src/engine/chromaprinter.h

@@ -0,0 +1,64 @@
+/*
+ * Strawberry Music Player
+ * This file was part of Clementine.
+ * Copyright 2012, David Sansome <me@davidsansome.com>
+ * Copyright 2019-2021, Jonas Kvinge <jonas@jkvinge.net>
+ *
+ * Strawberry is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Strawberry is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Strawberry.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef CHROMAPRINTER_H
+#define CHROMAPRINTER_H
+
+#include "config.h"
+
+#include <glib.h>
+#include <gst/gst.h>
+#include <gst/app/gstappsink.h>
+
+#include <QBuffer>
+#include <QString>
+
+class Chromaprinter {
+  // Creates a Chromaprint fingerprint from a song.
+  // Uses GStreamer to open and decode the file as PCM data and passes this to Chromaprint's code generator.
+  // The generated code can be used to identify a song via Acoustid.
+  // You should create one Chromaprinter for each file you want to fingerprint.
+  // This class works well with QtConcurrentMap.
+
+ public:
+  explicit Chromaprinter(const QString &filename);
+
+  // Creates a fingerprint from the song.
+  // This method is blocking, so you want to call it in another thread.
+  // Returns an empty string if no fingerprint could be created.
+  QString CreateFingerprint();
+
+ private:
+  GstElement *CreateElement(const QString &factory_name, GstElement *bin = nullptr);
+
+  static void NewPadCallback(GstElement*, GstPad *pad, gpointer data);
+  static GstFlowReturn NewBufferCallback(GstAppSink *app_sink, gpointer self);
+
+ private:
+  QString filename_;
+
+  GstElement *convert_element_;
+
+  QBuffer buffer_;
+
+};
+
+#endif  // CHROMAPRINTER_H