decoder, player: support song ranges

Seek the decoder to the start of the range before beginning with
playback.  Stop the decoder when the end of the range has been
reached.  Add the start position to the seek position.  Expose the
duration of the range, not the full song file.

src/decoder_api.c

@@ -328,8 +328,9 @@ decoder_data(struct decoder *decoder,
 		}
 
 		dest = music_chunk_write(chunk, &dc->out_audio_format,
-					 decoder->timestamp, kbit_rate,
+					 decoder->timestamp -
-					 &nbytes);
+					 dc->song->start_ms / 1000.0,
+					 kbit_rate, &nbytes);
 		if (dest == NULL) {
 			/* the chunk is full, flush it */
 			decoder_flush_chunk(decoder);
@@ -366,6 +367,12 @@ decoder_data(struct decoder *decoder,
 
 		decoder->timestamp += (double)nbytes /
 			audio_format_time_to_size(&dc->in_audio_format);
+
+		if (dc->song->end_ms > 0 &&
+		    decoder->timestamp >= dc->song->end_ms / 1000.0)
+			/* the end of this range has been reached:
+			   stop decoding */
+			return DECODE_COMMAND_STOP;
 	}
 
 	return DECODE_COMMAND_NONE;

src/player_thread.c

@@ -227,6 +227,26 @@ player_wait_for_decoder(struct player *player)
 	return true;
 }
 
+/**
+ * Returns the real duration of the song, comprising the duration
+ * indicated by the decoder plugin.
+ */
+static double
+real_song_duration(const struct song *song, double decoder_duration)
+{
+	assert(song != NULL);
+
+	if (decoder_duration <= 0.0)
+		/* the decoder plugin didn't provide information; fall
+		   back to song_get_duration() */
+		return song_get_duration(song);
+
+	if (song->end_ms > 0 && song->end_ms / 1000.0 < decoder_duration)
+		return (song->end_ms - song->start_ms) / 1000.0;
+
+	return decoder_duration - song->start_ms / 1000.0;
+}
+
 /**
  * The decoder has acknowledged the "START" command (see
  * player_wait_for_decoder()).  This function checks if the decoder
@@ -265,7 +285,7 @@ player_check_decoder_startup(struct player *player)
 			return true;
 
 		player_lock();
-		pc.total_time = dc->total_time;
+		pc.total_time = real_song_duration(dc->song, dc->total_time);
 		pc.audio_format = dc->in_audio_format;
 		player_unlock();
 
@@ -351,13 +371,14 @@ player_send_silence(struct player *player)
  */
 static bool player_seek_decoder(struct player *player)
 {
+	struct song *song = pc.next_song;
 	struct decoder_control *dc = player->dc;
 	double where;
 	bool ret;
 
 	assert(pc.next_song != NULL);
 
-	if (decoder_current_song(dc) != pc.next_song) {
+	if (decoder_current_song(dc) != song) {
 		/* the decoder is already decoding the "next" song -
 		   stop it and start the previous song again */
 
@@ -399,7 +420,7 @@ static bool player_seek_decoder(struct player *player)
 	if (where < 0.0)
 		where = 0.0;
 
-	ret = dc_seek(dc, where);
+	ret = dc_seek(dc, where + song->start_ms / 1000.0);
 	if (!ret) {
 		/* decoder failure */
 		player_command_finished();
@@ -801,11 +822,18 @@ static void do_play(struct decoder_control *dc)
 		if (player.decoder_starting) {
 			/* wait until the decoder is initialized completely */
 			bool success;
+			const struct song *song;
 
 			success = player_check_decoder_startup(&player);
 			if (!success)
 				break;
 
+			/* seek to the beginning of the range */
+			song = decoder_current_song(dc);
+			if (song != NULL && song->start_ms > 0 &&
+			    !dc_seek(dc, song->start_ms / 1000.0))
+				player_dc_stop(&player);
+
 			player_lock();
 			continue;
 		}