make some ogg/vorbis/flac functions public

ogg.go

@@ -120,6 +120,9 @@ func (o *oggDemuxer) Read(r io.Reader) ([][]byte, error) {
 	var packets [][]byte
 	var p int
 	for _, s := range segmentTable {
+		if !continued && !bytes.HasPrefix(segmentsData, vorbisCommentPrefix) && !bytes.HasPrefix(segmentsData, opusTagsPrefix) {
+			return nil, fmt.Errorf("not a metadata segment")
+		}
 		packetBuf.Write(segmentsData[p : p+int(s)])
 		if s < 255 {
 			packets = append(packets, packetBuf.Bytes())
@@ -150,15 +153,15 @@ func ReadOGGTags(r io.Reader) (Metadata, error) {
 			switch {
 			case bytes.HasPrefix(b, vorbisCommentPrefix):
 				m := &metadataOGG{
-					newMetadataVorbis(),
+					NewMetadataVorbis(),
 				}
-				err = m.readVorbisComment(bytes.NewReader(b[len(vorbisCommentPrefix):]))
+				err = m.ReadVorbisComment(bytes.NewReader(b[len(vorbisCommentPrefix):]))
 				return m, err
 			case bytes.HasPrefix(b, opusTagsPrefix):
 				m := &metadataOGG{
-					newMetadataVorbis(),
+					NewMetadataVorbis(),
 				}
-				err = m.readVorbisComment(bytes.NewReader(b[len(opusTagsPrefix):]))
+				err = m.ReadVorbisComment(bytes.NewReader(b[len(opusTagsPrefix):]))
 				return m, err
 			}
 		}
@@ -166,7 +169,7 @@ func ReadOGGTags(r io.Reader) (Metadata, error) {
 }
 
 type metadataOGG struct {
-	*metadataVorbis
+	*MetadataVorbis
 }
 
 func (m *metadataOGG) FileType() FileType {