func ReadFLACTags(r io.ReadSeeker) (Metadata, error) {
	flac, err := readString(r, 4)
	if err != nil {
		return nil, err
	}
	if flac != "fLaC" {
		return nil, errors.New("expected 'fLaC'")
	}
	m := &metadataFLAC{
		newMetadataVorbis(),
	}
	for {
		last, err := m.readFLACMetadataBlock(r)
		if err != nil {
			return nil, err
		}
		if last {
			break
		}
	}
	return m, nil
}
ReadFLACTags reads FLAC metadata from the io.ReadSeeker, returning the resulting
metadata in a Metadata implementation, or non-nil error if there was a problem.
package tag
import (
	"errors"
	"io"
)
type blockType byte
const (
	vorbisCommentBlock blockType = 4
	pictureBlock       blockType = 6
)