libsaria: Implement gapless playback

I need to get the next file out of the library or queue without changing
it immediately.  I then queue it up in the gstreamer pipeline so it will
play automatically when the current track finishes.

include/libsaria/controls.h

@@ -4,6 +4,7 @@
 namespace libsaria
 {
 	void next();
+	string next_file();
 	void set_pause_after(bool);
 	bool get_pause_after();
 	void toggle_play();

include/libsaria/library.h

@@ -24,9 +24,11 @@ namespace libsaria
 		void refresh();
 
 		void next();
+		string next_file();
 		void add_path(string);
 		void remove_path(string);
 		void play_id(ino_t &);
+		string find_filepath(ino_t &);
 		TrackTag *get_info(ino_t &);
 		void for_each(SourceModel *);
 		void for_each_path(void (*)(struct PathInfo &));

include/libsaria/queue.h

@@ -15,6 +15,7 @@ namespace libsaria
 		unsigned int size();
 
 		void next();
+		string next_file();
 
 	}
 }

libsaria/audio/audio.cpp

@@ -2,10 +2,12 @@
 #include <libsaria/audio.h>
 #include <libsaria/controls.h>
 #include <libsaria/print.h>
+#include <libsaria/library.h>
 #include <libsaria/callback.h>
 #include "audio.h"
 
 GstElement *player = NULL;
+GstElement *alsa = NULL;
 GstBus *bus = NULL;
 
 static void parse_error(GstMessage *error)
@@ -49,6 +51,16 @@ static gboolean on_message(GstBus *bus, GstMessage *message, gpointer data)
 	return TRUE;
 }
 
+static void about_to_finish(GstElement *playbin, gpointer data)
+{
+	string file;
+
+	println("About to finish!");
+	file = libsaria::next_file();
+	if (file != "")
+		load_file(playbin, file);
+}
+
 static void audio_changed(GstElement *playbin, gpointer data)
 {
 	GQuark quark = g_quark_from_string("audio-changed");
@@ -68,9 +80,15 @@ namespace libsaria
 		gst_init(&argc, &argv);
 
 		player = gst_element_factory_make("playbin2", "player");
+		alsa   = gst_element_factory_make("alsasink", "alsa");
 		bus    = gst_pipeline_get_bus(GST_PIPELINE(player));
 
 		gst_bus_add_watch(bus, on_message, NULL);
+
+		/* Without this gapless playback won't work */
+		g_object_set(G_OBJECT(player), "audio-sink", alsa, NULL);
+
+		g_signal_connect(player, "about-to-finish", G_CALLBACK(about_to_finish), NULL);
 		g_signal_connect(player, "audio-changed", G_CALLBACK(audio_changed), NULL);
 
 		set_volume(1.0);

libsaria/controls.cpp

@@ -23,6 +23,14 @@ namespace libsaria
 			audio::play();
 	}
 
+	string next_file()
+	{
+		if (queue::size() > 0)
+			return queue::next_file();
+		else
+			return library::next_file();
+	}
+
 	void set_pause_after(bool state)
 	{
 		pause_after_current = state;

libsaria/library/list.cpp

@@ -157,6 +157,14 @@ namespace libsaria
 		}
 	}
 
+	string library::find_filepath(ino_t &id)
+	{
+		list<TrackTag *>::iterator it;
+		if (find_id(id, it))
+			return (*it)->get_filepath();
+		return "";
+	}
+
 	TrackTag *library::get_info(ino_t &id)
 	{
 		list<TrackTag *>::iterator it;
@@ -165,20 +173,28 @@ namespace libsaria
 		return NULL;
 	}
 
-	void library::next()
+	string library::next_file()
 	{
 		string filepath = "";
 
-		if (libsaria::library::size() == 0) {
-			libsaria::audio::stop();
-			return;
-		}
+		if (libsaria::library::size() == 0)
+			return filepath;
 
 		do {
 			pick_next();
 			filepath = (*cur_track)->get_filepath();
 		} while (filepath == "");
-		libsaria::audio::load(filepath);
+
+		return filepath;
+	}
+
+	void library::next()
+	{
+		string filepath = next_file();
+		if (filepath != "")
+			libsaria::audio::load(filepath);
+		else
+			libsaria::audio::stop();
 	}
 
 	unsigned int library::size()

libsaria/queue/queue.cpp

@@ -9,6 +9,13 @@ using namespace std;
 
 static deque<ino_t> playqueue;
 
+static void pop_queue(ino_t &inode)
+{
+	inode = playqueue.front();
+	playqueue.pop_front();
+	trigger_callback(QUEUE_REFRESH);
+}
+
 namespace libsaria
 {
 
@@ -35,11 +42,18 @@ namespace libsaria
 		return playqueue.size();
 	}
 
+	string queue::next_file()
+	{
+		ino_t inode;
+		pop_queue(inode);
+		return library::find_filepath(inode);
+	}
+
 	void queue::next()
 	{
-		library::play_id(playqueue.front());
-		playqueue.pop_front();
-		trigger_callback(QUEUE_REFRESH);
+		ino_t inode;
+		pop_queue(inode);
+		library::play_id(inode);
 	}
 
 } /* Namespace: libsaria */