We've been using the Content-Duration header with http servers to provide the length (in time) of a particular Ogg physical bitstream. This speeds up ui display and, if Content-Length is also set, allows faster seeking dispatch over remote protocols by priming the binary search with an initial average bitrate.
Older applications used X-Content-Duration instead. This SHOULD be supported by user agents for backwards compatibility with older server implementations, but new servers should use Content-Duration. This page is a draft spec for registering that message header.
PROVISIONAL MESSAGE HEADER FIELD SUBMISSION TEMPLATE
Header field name: The name proposed for the new header field. This SHOULD conform to the field name specification details noted in Section 4.1.
Applicable protocol: Specify "mail" (RFC 2822), "mime" (RFC 2045), "http" (RFC 2616), "netnews" (RFC 1036), or cite any other standards-track RFC defining the protocol with which the header is intended to be used.
Status: Specify: "provisional". This will be updated if and when the header registration is subsequently moved to the permanent registry.
Author/Change controller: The name, email address, and organization name of the submission author, who may authorize changes to or retraction of the repository entry. A postal address, home page URI, telephone and fax numbers may also be included. If the proposal comes from a standards body working group, give the name and home page URI of the working group, and an email address for discussion of or comments on the specification.
Specification document(s): Reference to document that specifies the header for use with the indicated protocol. The document MUST be an RFC, a current Internet-draft or the URL of a publicly accessible document (so IANA can verify availability of the specification). An indication of the relevant sections MAY also be included, but is not required.
NOTE: if the specification is available in printed form only, then an Internet draft containing full reference to the paper document should be published and cited in the registration template. The paper specification MAY be cited under related information.
Related information: Optionally, citations to additional documents containing further relevant information.