(RFC 5405 published January 2009) Media Type Definition The media type for the G.719 codec is allocated from the IETF tree since G.719 has the potential to become a widely used audio codec in general Voice over IP (VoIP), teleconferencing, and streaming applications. This media type registration covers real-time transfer via RTP. Note, any unspecified parameter MUST be ignored by the receiver to ensure that additional parameters can be added in any future revision of this specification. Type name: audio Subtype name: G719 Required parameters: none Optional parameters: interleaving: Indicates that interleaved mode SHALL be used for the payload. The parameter specifies the number of frame-block slots available in a de-interleaving buffer (including the frame that is ready to be consumed) for each source. Its value is equal to one plus the maximum number of frames that can precede any frame in transmission order and follow the frame in RTP timestamp order. The value MUST be greater than zero. If this parameter is not present, interleaved mode SHALL NOT be used. int-delay: The minimal media time delay in milliseconds that is needed to avoid underrun in the de-interleaving buffer before starting decoding, i.e., the difference in RTP timestamp ticks between the earliest and latest audio frame present in the de- interleaving buffer expressed in milliseconds. The value is a stream property and provided per source. The allowed values are zero to the largest value expressible by an unsigned 16-bit integer (65535). Please note that in practice, the largest value that can be used is equal to the declared size of the interleaving buffer of the receiver. If the value for some reason is larger than the receiver buffer declared by or for the receiver, this value defaults to the size of the receiver buffer. For sources for which this value hasn't been provided, the value defaults to the size of the receiver buffer. The format is a comma-separated list of synchronization source (SSRC) ":" delay in ms pairs, which in ABNF [RFC5234] is expressed as: int-delay = "int-delay=" source-delay *("," source-delay) source-delay = SSRC ":" delay-value SSRC = 1*8HEXDIG ; The 32-bit SSRC encoded in hex format delay-value = 1*5DIGIT ; The delay value in milliseconds Example: int-delay=ABCD1234:1000,4321DCB:640 NOTE: No white space allowed in the parameter before the end of all the value pairs max-red: The maximum duration in milliseconds that elapses between the primary (first) transmission of a frame and any redundant transmission that the sender will use. This parameter allows a receiver to have a bounded delay when redundancy is used. Allowed values are between zero (no redundancy will be used) and 65535. If the parameter is omitted, no limitation on the use of redundancy is present. channels: The number of audio channels. The possible values (1-6) and their respective channel order is specified in Section 4.1 of [RFC3551]. If omitted, it has the default value of 1. CBR: Constant Bitrate (CBR) indicates the exact codec bitrate in bits per second (not including the overhead from packetization, RTP header, or lower layers) that the codec MUST use. "CBR" is to be used when the dynamic rate cannot be supported (one case is, e.g., gateway to H.320). "CBR" is mostly used for gateways to circuit switch networks. Therefore, the "CBR" is the rate not including any FEC as specified in Section 4.3.1. If FEC is to be used, the "b=" parameter MUST be used to allow the extra bitrate needed to send the redundant information. It is RECOMMENDED that this parameter is only used when necessary to establish a working communication. The usage of this parameter has implications for congestion control that need to be considered; see Section 9. ptime: see [RFC8866]. maxptime: see [RFC8866]. Encoding considerations: This media type is framed and binary; see Section 4.8 of [RFC4288]. Security considerations: See Section 10 of RFC 5404. Interoperability considerations: The support of the Interleaving mode is not mandatory and needs to be negotiated. See Section 7.2 for how to do that for SDP-based protocols. Published specification: RFC 5404 Applications that use this media type: Real-time audio applications like Voice over IP and teleconference, and multi-media streaming. Additional information: none Person & email address to contact for further information: Ingemar Johansson Intended usage: COMMON Restrictions on usage: This media type depends on RTP framing, and hence is only defined for transfer via RTP [RFC3550]. Transport within other framing protocols is not defined at this time. Author: Ingemar Johansson Magnus Westerlund Change controller: IETF Audio/Video Transport working group delegated from the IESG. Additionally, note that file storage of G.719-encoded audio in ISO base media file format is specified in Annex A of [ITU-T-G719]. Thus, media file formats such as MP4 (audio/mp4 or video/mp4) [RFC4337] and 3GP (audio/3GPP and video/3GPP) [RFC3839] can contain G.719-encoded audio.