Currently, kFormatCodecMappings maps a container name to a string containing a comma-separated list of codec strings. This is confusing since it appears all codec strings are listed and involves unnecessary processing of the strings to determine the corresponding MimeUtil::Codec enum value. It can also lead to confusion, such as that some values are allowed while other are not (e.g.  issue 589675 ).

It would be better to start with a list of MimeUtil::Codec enum values.