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: Content-Duration The name proposed for the new header field. This SHOULD conform to the field name specification details noted in Section 4.1.
Applicable protocol: http (applicable to mime in general?) 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: provisional Specify: "provisional". This will be updated if and when the header registration is subsequently moved to the permanent registry.
Author/Change controller: Ralph Giles <firstname.lastname@example.org> Xiph.org Foundation 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): http://wiki.xiph.org/ContentDuration 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.
Related information: Optionally, citations to additional documents containing further relevant information.