fix vorbis multiple artists

vorbis.go

@@ -22,7 +22,7 @@ func newMetadataVorbis() *metadataVorbis {
 }
 
 type metadataVorbis struct {
-	c map[string]string // the vorbis comments
+	c map[string]string // the vorbis commentsq
 	p *Picture
 }
 
@@ -43,6 +43,8 @@ func (m *metadataVorbis) readVorbisComment(r io.Reader) error {
 		return err
 	}
 
+	artists := []string{}
+
 	for i := uint32(0); i < commentsLen; i++ {
 		l, err := readUint32LittleEndian(r)
 		if err != nil {
@@ -56,9 +58,15 @@ func (m *metadataVorbis) readVorbisComment(r io.Reader) error {
 		if err != nil {
 			return err
 		}
+
+		if k == "ARTIST" {
+			artists = append(artists, v)
+		}
 		m.c[strings.ToLower(k)] = v
 	}
 
+	m.c["artist"] = strings.Join(artists, ";")
+
 	if b64data, ok := m.c["metadata_block_picture"]; ok {
 		data, err := base64.StdEncoding.DecodeString(b64data)
 		if err != nil {
@@ -151,6 +159,7 @@ func parseComment(c string) (k, v string, err error) {
 		err = errors.New("vorbis comment must contain '='")
 		return
 	}
+
 	k = kv[0]
 	v = kv[1]
 	return