(registered in RFC3555)

MIME media type name: audio

MIME subtype name: RED

Required parameters:
     pt: a comma-separated list of RTP payload types.  Because
     comma is a special character, the list must be a quoted-string
     (enclosed in double quotes).  For static payload types, each
     list element is simply the type number.  For dynamic payload
     types, each list element is a mapping of the dynamic payload
     type number to an embedded MIME content-type specification for
     the payload format corresponding to the dynamic payload type.
     The format of the mapping is:

        dynamic-payload-type "=" content-type

     If the content-type string includes a comma, then the
     content-type string MUST be a quoted-string.  If the content-
     type string does not include a comma, it MAY still be quoted.
     Since it is part of the list which must itself be a quoted-
     string, that means the quotation marks MUST be quoted with
     backslash quoting as specified in RFC 2045.  If the content-
     type string itself contains a quoted-string, then the
     requirement for backslash quoting is recursively applied.  To
     specify the audio/RED payload format in SDP, the pt parameter
     is mapped to an a=fmtp attribute by eliminating the parameter
     name (pt) and changing the commas to slashes.  For example,
     'pt="0,5"' maps to 'a=fmtp:99 0/5'.  A more complicated
     example, with a dynamic payload type, is:

        pt = "0, 103 = \"audio/G729D;annexb=yes\" "

        m=audio 49170 RTP/AVP 99 0 103
        a=rtpmap:99 RED/8000
        a=fmtp:99 0/103
        a=rtpmap:103 G729D/8000
        a=fmtp:103 annexb=yes

Optional parameters: ptime, maxptime

Encoding considerations:
     This type is only defined for transfer via RTP [RFC 3550].

Security considerations: See Section 5 of RFC 3555

Interoperability considerations: none

Published specification: RFC 2198

Applications which use this media type:
     Audio and video streaming and conferencing tools.

Additional information: none

Person & email address to contact for further information:
     Stephen Casner <casner&acm.org>

Intended usage: COMMON

Author/Change controller:
     Stephen Casner