sequence.go
func (s *FileSequence) Start() int {
	if s.frameSet == nil {
		return 0
	}
	return s.frameSet.Start()
}
func (s *FileSequence) Start() int {
	if s.frameSet == nil {
		return 0
	}
	return s.frameSet.Start()
}
// Start returns the starting frame of the sequence.
// If a frame range/number could not be parsed, then this
// will always return 0