Add support for lyrics.

Not supported in id3v1 and id3v22

flac.go

@@ -288,6 +288,10 @@ func (m *metadataFLAC) Disc() (int, int) {
 	return x, n
 }
 
+func (m *metadataFLAC) Lyrics() string {
+	return m.c["lyrics"]
+}
+
 func (m *metadataFLAC) Picture() *Picture {
 	return m.p
 }

id3v1.go

@@ -134,3 +134,4 @@ func (m metadataID3v1) AlbumArtist() string { return "" }
 func (m metadataID3v1) Composer() string    { return "" }
 func (metadataID3v1) Disc() (int, int)      { return 0, 0 }
 func (m metadataID3v1) Picture() *Picture   { return nil }
+func (m metadataID3v1) Lyrics() string      { return "" }

id3v2.go

@@ -218,6 +218,13 @@ func readID3v2Frames(r io.Reader, h *ID3v2Header) (map[string]interface{}, error
 			}
 			result[rawName] = txt
 
+		case name == "COMM" || name == "USLT":
+			t, err := readTextWithDescrFrame(b)
+			if err != nil {
+				return nil, err
+			}
+			result[rawName] = t
+
 		case name == "APIC":
 			p, err := readAPICFrame(b)
 			if err != nil {

id3v2frames.go

@@ -81,6 +81,21 @@ func decodeUTF16(b []byte, bo binary.ByteOrder) string {
 	return string(utf16.Decode(s))
 }
 
+// Comm is a type used in COMM and USLT tag. It's a text with a description and
+// a specified language
+
+type Comm struct {
+	Language    string
+	Description string
+	Text        string
+}
+
+// String returns a string representation of the underlying Comm instance.
+func (t Comm) String() string {
+	return fmt.Sprintf("Text{Lang: '%v', Description: '%v', %v lines}",
+		t.Language, t.Description, strings.Count(t.Text, "\n"))
+}
+
 var pictureTypes = map[byte]string{
 	0x00: "Other",
 	0x01: "32x32 pixels 'file icon' (PNG only)",
@@ -158,6 +173,35 @@ func readPICFrame(b []byte) (*Picture, error) {
 	}, nil
 }
 
+// IDv2.{3,4}
+// -- Header
+// <Header for 'Unsynchronised lyrics/text transcription', ID: "USLT">
+// <Header for 'Comment', ID: "COMM">
+// -- readTextWithDescrFrame
+// Text encoding       $xx
+// Language            $xx xx xx
+// Content descriptor  <text string according to encoding> $00 (00)
+// Lyrics/text         <full text string according to encoding>
+func readTextWithDescrFrame(b []byte) (*Comm, error) {
+	enc := b[0]
+	descTextSplit := bytes.SplitN(b[4:], []byte{0}, 2)
+	desc, err := decodeText(enc, descTextSplit[0])
+	if err != nil {
+		return nil, fmt.Errorf("error decoding tag description text: %v", err)
+	}
+
+	text, err := decodeText(enc, descTextSplit[1])
+	if err != nil {
+		return nil, fmt.Errorf("error decoding tag description text: %v", err)
+	}
+
+	return &Comm{
+		Language:    string(b[1:4]),
+		Description: desc,
+		Text:        text,
+	}, nil
+}
+
 // IDv2.{3,4}
 // -- Header
 // <Header for 'Attached picture', ID: "APIC">

id3v2metadata.go

@@ -37,6 +37,7 @@ var frames = frameNames(map[string][2]string{
 	"disc":         [2]string{"TPA", "TPOS"},
 	"genre":        [2]string{"TCO", "TCON"},
 	"picture":      [2]string{"PIC", "APIC"},
+	"lyrics":       [2]string{"", "USLT"},
 })
 
 // metadataID3v2 is the implementation of Metadata used for ID3v2 tags.
@@ -112,6 +113,14 @@ func (m metadataID3v2) Disc() (int, int) {
 	return parseXofN(m.getString(frames.Name("disc", m.Format())))
 }
 
+func (m metadataID3v2) Lyrics() string {
+	t, ok := m.frames[frames.Name("lyrics", m.Format())]
+	if !ok {
+		return ""
+	}
+	return t.(*Comm).Text
+}
+
 func (m metadataID3v2) Picture() *Picture {
 	v, ok := m.frames[frames.Name("picture", m.Format())]
 	if !ok {

mp4.go

@@ -222,6 +222,14 @@ func (m metadataMP4) Disc() (int, int) {
 	return x, 0
 }
 
+func (m metadataMP4) Lyrics() string {
+	t, ok := m["\xa9lyr"]
+	if !ok {
+		return ""
+	}
+	return t.(string)
+}
+
 func (m metadataMP4) Picture() *Picture {
 	v, ok := m["covr"]
 	if !ok {

tag.go

@@ -87,9 +87,12 @@ type Metadata interface {
 	// Disc returns the disc number and total discs, or zero values if unavailable.
 	Disc() (int, int)
 
-	// Picture returns a picture, or nil if not avilable.
+	// Picture returns a picture, or nil if not available.
 	Picture() *Picture
 
+	// Lyrics returns the lyrics, or an empty string if unavailable.
+	Lyrics() string
+
 	// Raw returns the raw mapping of retrieved tag names and associated values.
 	// NB: tag/atom names are not standardised between formats.
 	Raw() map[string]interface{}