func (s *Stream) Seek(offset int64, whence int) (int64, error) {
	return s.decoded.Seek(offset, whence)
}
func (s *Stream) Seek(offset int64, whence int) (int64, error) {
	return s.decoded.Seek(offset, whence)
}
// Seek is implementation of io.Seeker's Seek.
//
// Note that Seek can take long since decoding is a relatively heavy task.