A length indicator (23) associated with an encoded representation (20) of a slice (3) is parsed. The length indicator (23) is indicative of a length of an extension field (24) present in a slice header (21) of the encoded representation (20). A decoder (40) can then determine to ignore, during decoding of the encoded representation (20), any value of the extension field (24) in the slice header (21) where these values are identified based on the length indicator (23). As a consequence, extension fields (23) can be added to slice headers (21) and still enable legacy decoders (40) to correctly decode the encoded representations (20).