add song duration for flac files

src/metadata.rs

@@ -146,12 +146,18 @@ fn read_flac(path: &Path) -> Result<SongTags> {
 		.get("DISCNUMBER")
 		.and_then(|d| d[0].parse::<u32>().ok());
 	let year = vorbis.get("DATE").and_then(|d| d[0].parse::<i32>().ok());
+	let streaminfo = tag.get_blocks(metaflac::BlockType::StreamInfo);
+	let duration = match streaminfo.first() {
+        Some(&&metaflac::Block::StreamInfo(ref s)) => (s.total_samples as u32 / s.sample_rate) as u32,
+        _ => 0
+	};
+
 	Ok(SongTags {
 	       artist: vorbis.artist().map(|v| v[0].clone()),
 	       album_artist: vorbis.album_artist().map(|v| v[0].clone()),
 	       album: vorbis.album().map(|v| v[0].clone()),
 	       title: vorbis.title().map(|v| v[0].clone()),
-	       duration: None,
+	       duration: Some(duration),
 	       disc_number: disc_number,
 	       track_number: vorbis.track(),
 	       year: year,