codec.go
func (reg *Registry) Codecs() (codecs map[string]Codec) {
	codecs = make(map[string]Codec)
	reg.mutex.RLock()
	for mimetype, codec := range reg.codecs {
		codecs[mimetype] = codec
	}
	reg.mutex.RUnlock()
	return
}
func (reg *Registry) Codecs() (codecs map[string]Codec) {
	codecs = make(map[string]Codec)
	reg.mutex.RLock()
	for mimetype, codec := range reg.codecs {
		codecs[mimetype] = codec
	}
	reg.mutex.RUnlock()
	return
}
// Codecs returns a map of all codecs registered in reg.