http://www.rfc-editor.org/rfc/rfc4281.txt
RFC 4281: The Codecs Parameter for "Bucket" Media Types, R. Gellens, D. Singer, P. Frojdh2005-11-01T23:00:00-00:00By labeling content with the specific codecs indicated to render the contained media, receiving systems can determine if the codecs are supported by the end system, and if not, can take appropriate action (such as rejecting the content, sending notification of the situation, transcoding the content to a supported type, fetching and installing the required codecs, further inspection to determine if it will be sufficient to support a subset of the indicated codecs, etc.) [STANDARDS-TRACK]