(RFC 3558 published July 2003, updated January 2007 per RFC4788)

Type name:  audio

Subtype names:  EVRC

Required parameters:  none

Optional parameters:

   ptime:  Defined as usual for RTP audio (see RFC8866).

   maxptime:  The maximum amount of media that can be encapsulated in
      each packet, expressed as time in milliseconds.  The time SHALL
      be calculated as the sum of the time the media present in the
      packet represents.  The time SHOULD be a multiple of the
      duration of a single codec data frame (20 msec).  If not
      signaled, the default maxptime value SHALL be 200 milliseconds.

   maxinterleave:  Maximum number for interleaving length (field LLL
      in the Interleaving Octet).  The interleaving lengths used in
      the entire session MUST NOT exceed this maximum value.  If not
      signaled, the maxinterleave length SHALL be 5.

   silencesupp:  see Section 6.1 for definition.  If this parameter
      is not present, the default value 1 MUST be assumed.

   dtxmax:  see Section 6.1

   dtxmin:  see Section 6.1

   hangover:  see Section 6.1

Encoding considerations:
   This media type is framed binary data (see RFC 4288, Section 4.8),
   and is defined for transfer of EVRC-encoded data via RTP using the
   Interleaved/Bundled packet format specified in Sections 4.1, 6,
   and 7 of RFC 3558.  It is also defined for other transfer methods
   using the storage format specified in Section 11 of RFC 3558.

Security considerations:  See Section 14, "Security Considerations",
   of RFC 3558.

Interoperability considerations:
   The DTX parameters are receiver options.  Existing RFC 3558
   implementations will not send any of the DTX parameters in their
   SDP and will ignore any DTX parameters they receive.  The adaptive
   DTX behavior of DTX-capable EVRC codecs (as detailed in [8],
   Section 4.3.5) ensures interoperability with non-DTX EVRC codecs.

Published specification:
   The EVRC vocoder is specified in 3GPP2 C.S0014 [2].  Transfer
   methods are specified in RFC 3558.

Applications that use this media type:
   It is expected that many VoIP applications (as well as mobile
   applications) will use this type.

Additional information:
   The following information applies for storage format only.

      Magic number: #!EVRC\n (see Section 11 of RFC 3558)
      File extensions: evc, EVC
      Macintosh file type code: none
      Object identifier or OID: none

Person & email address to contact for further information:
   Qiaobing Xie <Qiaobing.Xie&motorola.com>

Intended usage:  COMMON

Restrictions on usage:
   This media type may be used with RTP framing (RFC 3550 [5]) and as
   a storage format.  When used with RTP, the procedures in RFC 3558,
   Section 4.1, MUST be followed.  In all other contexts, the storage
   format defined in RFC 3558, Section 11, MUST be used.

Author:
   Adam Li/Qiaobing Xie

Change controller:
   IETF Audio/Video Transport working group delegated from the IESG.