Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 1 | <?xml version="1.0" encoding="UTF-8"?> |
| 2 | <!DOCTYPE rfc SYSTEM "rfc2629.dtd" [ |
| 3 | <!ENTITY rfc2119 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml'> |
Jean-Marc Valin | f3d6c7a | 2014-06-30 14:13:46 -0400 | [diff] [blame] | 4 | <!ENTITY rfc3389 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3389.xml'> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 5 | <!ENTITY rfc3550 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3550.xml'> |
| 6 | <!ENTITY rfc3711 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3711.xml'> |
| 7 | <!ENTITY rfc3551 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3551.xml'> |
Jean-Marc Valin | d10755e | 2014-11-19 11:07:50 -0500 | [diff] [blame] | 8 | <!ENTITY rfc6838 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.6838.xml'> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 9 | <!ENTITY rfc4855 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4855.xml'> |
| 10 | <!ENTITY rfc4566 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4566.xml'> |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 11 | <!ENTITY rfc4585 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4585.xml'> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 12 | <!ENTITY rfc3264 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3264.xml'> |
| 13 | <!ENTITY rfc2974 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2974.xml'> |
| 14 | <!ENTITY rfc2326 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2326.xml'> |
| 15 | <!ENTITY rfc3555 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3555.xml'> |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 16 | <!ENTITY rfc5124 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.5124.xml'> |
Jean-Marc Valin | 5b20cb0 | 2015-04-21 20:33:42 -0400 | [diff] [blame] | 17 | <!ENTITY rfc5405 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.5405.xml'> |
Timothy B. Terriberry | 239e9a3 | 2012-11-21 18:48:09 -0800 | [diff] [blame] | 18 | <!ENTITY rfc5576 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.5576.xml'> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 19 | <!ENTITY rfc6562 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.6562.xml'> |
Jean-Marc Valin | acf0675 | 2012-11-22 17:10:50 -0500 | [diff] [blame] | 20 | <!ENTITY rfc6716 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.6716.xml'> |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 21 | <!ENTITY rfc7202 PUBLIC '' 'http://xml.resource.org/public/rfc/bibxml/reference.RFC.7202.xml'> |
Jean-Marc Valin | 5771b5a | 2013-08-02 12:04:50 -0400 | [diff] [blame] | 22 | <!ENTITY nbsp " "> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 23 | ]> |
| 24 | |
Jean-Marc Valin | 5b20cb0 | 2015-04-21 20:33:42 -0400 | [diff] [blame] | 25 | <rfc category="std" ipr="trust200902" docName="draft-ietf-payload-rtp-opus-11"> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 26 | <?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?> |
| 27 | |
| 28 | <?rfc strict="yes" ?> |
| 29 | <?rfc toc="yes" ?> |
| 30 | <?rfc tocdepth="3" ?> |
| 31 | <?rfc tocappendix='no' ?> |
| 32 | <?rfc tocindent='yes' ?> |
| 33 | <?rfc symrefs="yes" ?> |
| 34 | <?rfc sortrefs="yes" ?> |
| 35 | <?rfc compact="no" ?> |
| 36 | <?rfc subcompact="yes" ?> |
| 37 | <?rfc iprnotified="yes" ?> |
| 38 | |
| 39 | <front> |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 40 | <title abbrev="RTP Payload Format for Opus"> |
| 41 | RTP Payload Format for the Opus Speech and Audio Codec |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 42 | </title> |
| 43 | |
| 44 | <author fullname="Julian Spittka" initials="J." surname="Spittka"> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 45 | <address> |
Jean-Marc Valin | acf0675 | 2012-11-22 17:10:50 -0500 | [diff] [blame] | 46 | <email>jspittka@gmail.com</email> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 47 | </address> |
| 48 | </author> |
| 49 | |
| 50 | <author initials='K.' surname='Vos' fullname='Koen Vos'> |
Jean-Marc Valin | 49e6c05 | 2014-01-17 14:05:37 -0500 | [diff] [blame] | 51 | <organization>vocTone</organization> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 52 | <address> |
| 53 | <postal> |
Jean-Marc Valin | 49e6c05 | 2014-01-17 14:05:37 -0500 | [diff] [blame] | 54 | <street></street> |
| 55 | <code></code> |
| 56 | <city></city> |
| 57 | <region></region> |
| 58 | <country></country> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 59 | </postal> |
Jean-Marc Valin | acf0675 | 2012-11-22 17:10:50 -0500 | [diff] [blame] | 60 | <email>koenvos74@gmail.com</email> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 61 | </address> |
| 62 | </author> |
| 63 | |
| 64 | <author initials="JM" surname="Valin" fullname="Jean-Marc Valin"> |
| 65 | <organization>Mozilla</organization> |
| 66 | <address> |
| 67 | <postal> |
Jean-Marc Valin | e070300 | 2014-07-30 13:41:28 -0400 | [diff] [blame] | 68 | <street>331 E. Evelyn Avenue</street> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 69 | <city>Mountain View</city> |
| 70 | <region>CA</region> |
| 71 | <code>94041</code> |
| 72 | <country>USA</country> |
| 73 | </postal> |
| 74 | <email>jmvalin@jmvalin.ca</email> |
| 75 | </address> |
| 76 | </author> |
| 77 | |
Jean-Marc Valin | 5b20cb0 | 2015-04-21 20:33:42 -0400 | [diff] [blame] | 78 | <date day='14' month='April' year='2015' /> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 79 | |
| 80 | <abstract> |
| 81 | <t> |
| 82 | This document defines the Real-time Transport Protocol (RTP) payload |
| 83 | format for packetization of Opus encoded |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 84 | speech and audio data necessary to integrate the codec in the |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 85 | most compatible way. It also provides an applicability statement |
| 86 | for the use of Opus over RTP. Further, it describes media type registrations |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 87 | for the RTP payload format. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 88 | </t> |
| 89 | </abstract> |
| 90 | </front> |
| 91 | |
| 92 | <middle> |
| 93 | <section title='Introduction'> |
| 94 | <t> |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 95 | Opus <xref target="RFC6716"/> is a speech and audio codec developed within the |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 96 | IETF Internet Wideband Audio Codec working group. The codec |
Jean-Marc Valin | 15f0f1f | 2012-11-29 09:24:54 -0500 | [diff] [blame] | 97 | has a very low algorithmic delay and it |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 98 | is highly scalable in terms of audio bandwidth, bitrate, and |
| 99 | complexity. Further, it provides different modes to efficiently encode speech signals |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 100 | as well as music signals, thus making it the codec of choice for |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 101 | various applications using the Internet or similar networks. |
| 102 | </t> |
| 103 | <t> |
| 104 | This document defines the Real-time Transport Protocol (RTP) |
| 105 | <xref target="RFC3550"/> payload format for packetization |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 106 | of Opus encoded speech and audio data necessary to |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 107 | integrate Opus in the |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 108 | most compatible way. It also provides an applicability statement |
| 109 | for the use of Opus over RTP. |
| 110 | Further, it describes media type registrations for |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 111 | the RTP payload format. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 112 | </t> |
| 113 | </section> |
| 114 | |
| 115 | <section title='Conventions, Definitions and Acronyms used in this document'> |
| 116 | <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", |
| 117 | "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this |
| 118 | document are to be interpreted as described in <xref target="RFC2119"/>.</t> |
| 119 | <t> |
| 120 | <list style='hanging'> |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 121 | <t hangText="audio bandwidth:"> The range of audio frequecies being coded</t> |
Jean-Marc Valin | 15f0f1f | 2012-11-29 09:24:54 -0500 | [diff] [blame] | 122 | <t hangText="CBR:"> Constant bitrate</t> |
| 123 | <t hangText="CPU:"> Central Processing Unit</t> |
| 124 | <t hangText="DTX:"> Discontinuous transmission</t> |
| 125 | <t hangText="FEC:"> Forward error correction</t> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 126 | <t hangText="IP:"> Internet Protocol</t> |
| 127 | <t hangText="samples:"> Speech or audio samples (per channel)</t> |
| 128 | <t hangText="SDP:"> Session Description Protocol</t> |
Jean-Marc Valin | 15f0f1f | 2012-11-29 09:24:54 -0500 | [diff] [blame] | 129 | <t hangText="VBR:"> Variable bitrate</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 130 | </list> |
| 131 | </t> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 132 | <t> |
| 133 | Throughout this document, we refer to the following definitions: |
| 134 | </t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 135 | <texttable anchor='bandwidth_definitions'> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 136 | <ttcol align='center'>Abbreviation</ttcol> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 137 | <ttcol align='center'>Name</ttcol> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 138 | <ttcol align='center'>Audio Bandwidth (Hz)</ttcol> |
| 139 | <ttcol align='center'>Sampling Rate (Hz)</ttcol> |
| 140 | <c>NB</c> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 141 | <c>Narrowband</c> |
| 142 | <c>0 - 4000</c> |
| 143 | <c>8000</c> |
| 144 | |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 145 | <c>MB</c> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 146 | <c>Mediumband</c> |
| 147 | <c>0 - 6000</c> |
| 148 | <c>12000</c> |
| 149 | |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 150 | <c>WB</c> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 151 | <c>Wideband</c> |
| 152 | <c>0 - 8000</c> |
| 153 | <c>16000</c> |
| 154 | |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 155 | <c>SWB</c> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 156 | <c>Super-wideband</c> |
| 157 | <c>0 - 12000</c> |
| 158 | <c>24000</c> |
| 159 | |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 160 | <c>FB</c> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 161 | <c>Fullband</c> |
| 162 | <c>0 - 20000</c> |
| 163 | <c>48000</c> |
| 164 | |
| 165 | <postamble> |
| 166 | Audio bandwidth naming |
| 167 | </postamble> |
| 168 | </texttable> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 169 | </section> |
| 170 | |
| 171 | <section title='Opus Codec'> |
| 172 | <t> |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 173 | Opus encodes speech |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 174 | signals as well as general audio signals. Two different modes can be |
| 175 | chosen, a voice mode or an audio mode, to allow the most efficient coding |
| 176 | depending on the type of the input signal, the sampling frequency of the |
| 177 | input signal, and the intended application. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 178 | </t> |
| 179 | |
| 180 | <t> |
Jean-Marc Valin | 57fa056 | 2012-11-09 14:30:25 -0500 | [diff] [blame] | 181 | The voice mode allows efficient encoding of voice signals at lower bit |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 182 | rates while the audio mode is optimized for general audio signals at medium and |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 183 | higher bitrates. |
| 184 | </t> |
| 185 | |
| 186 | <t> |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 187 | Opus is highly scalable in terms of audio |
Jean-Marc Valin | 57fa056 | 2012-11-09 14:30:25 -0500 | [diff] [blame] | 188 | bandwidth, bitrate, and complexity. Further, Opus allows |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 189 | transmitting stereo signals with in-band signaling in the bit-stream. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 190 | </t> |
| 191 | |
| 192 | <section title='Network Bandwidth'> |
| 193 | <t> |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 194 | Opus supports bitrates from 6 kb/s to 510 kb/s. |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 195 | The bitrate can be changed dynamically within that range. |
| 196 | All |
| 197 | other parameters being |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 198 | equal, higher bitrates result in higher audio quality. |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 199 | </t> |
| 200 | <section title='Recommended Bitrate' anchor='bitrate_by_bandwidth'> |
| 201 | <t> |
| 202 | For a frame size of |
| 203 | 20 ms, these |
| 204 | are the bitrate "sweet spots" for Opus in various configurations: |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 205 | |
| 206 | <list style="symbols"> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 207 | <t>8-12 kb/s for NB speech,</t> |
| 208 | <t>16-20 kb/s for WB speech,</t> |
| 209 | <t>28-40 kb/s for FB speech,</t> |
| 210 | <t>48-64 kb/s for FB mono music, and</t> |
| 211 | <t>64-128 kb/s for FB stereo music.</t> |
| 212 | </list> |
| 213 | </t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 214 | </section> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 215 | <section title='Variable versus Constant Bitrate' anchor='variable-vs-constant-bitrate'> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 216 | <t> |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 217 | For the same average bitrate, variable bitrate (VBR) can achieve higher audio quality |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 218 | than constant bitrate (CBR). For the majority of voice transmission applications, VBR |
| 219 | is the best choice. One reason for choosing CBR is the potential |
| 220 | information leak that <spanx style='emph'>might</spanx> occur when encrypting the |
| 221 | compressed stream. See <xref target="RFC6562"/> for guidelines on when VBR is |
| 222 | appropriate for encrypted audio communications. In the case where an existing |
| 223 | VBR stream needs to be converted to CBR for security reasons, then the Opus padding |
| 224 | mechanism described in <xref target="RFC6716"/> is the RECOMMENDED way to achieve padding |
| 225 | because the RTP padding bit is unencrypted.</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 226 | |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 227 | <t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 228 | The bitrate can be adjusted at any point in time. To avoid congestion, |
Timothy B. Terriberry | 1e87fea | 2014-07-25 22:33:55 -0700 | [diff] [blame] | 229 | the average bitrate SHOULD NOT exceed the available |
Jean-Marc Valin | 66611f1 | 2015-01-13 09:19:24 -0500 | [diff] [blame] | 230 | network bandwidth. If no target bitrate is specified, the bitrates specified in |
Jean-Marc Valin | acf0675 | 2012-11-22 17:10:50 -0500 | [diff] [blame] | 231 | <xref target='bitrate_by_bandwidth'/> are RECOMMENDED. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 232 | </t> |
| 233 | |
| 234 | </section> |
| 235 | |
| 236 | <section title='Discontinuous Transmission (DTX)'> |
| 237 | |
| 238 | <t> |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 239 | Opus can, as described in <xref target='variable-vs-constant-bitrate'/>, |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 240 | be operated with a variable bitrate. In that case, the encoder will |
| 241 | automatically reduce the bitrate for certain input signals, like periods |
| 242 | of silence. When using continuous transmission, it will reduce the |
| 243 | bitrate when the characteristics of the input signal permit, but |
| 244 | will never interrupt the transmission to the receiver. Therefore, the |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 245 | received signal will maintain the same high level of audio quality over the |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 246 | full duration of a transmission while minimizing the average bit |
| 247 | rate over time. |
| 248 | </t> |
| 249 | |
| 250 | <t> |
| 251 | In cases where the bitrate of Opus needs to be reduced even |
| 252 | further or in cases where only constant bitrate is available, |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 253 | the Opus encoder can use discontinuous |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 254 | transmission (DTX), where parts of the encoded signal that |
| 255 | correspond to periods of silence in the input speech or audio signal |
Jean-Marc Valin | f3d6c7a | 2014-06-30 14:13:46 -0400 | [diff] [blame] | 256 | are not transmitted to the receiver. A receiver can distinguish |
| 257 | between DTX and packet loss by looking for gaps in the sequence |
| 258 | number, as described by Section 4.1 |
| 259 | of <xref target="RFC3551"/>. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 260 | </t> |
| 261 | |
| 262 | <t> |
| 263 | On the receiving side, the non-transmitted parts will be handled by a |
| 264 | frame loss concealment unit in the Opus decoder which generates a |
| 265 | comfort noise signal to replace the non transmitted parts of the |
Jean-Marc Valin | f3d6c7a | 2014-06-30 14:13:46 -0400 | [diff] [blame] | 266 | speech or audio signal. Use of <xref target="RFC3389"/> Comfort |
| 267 | Noise (CN) with Opus is discouraged. |
| 268 | The transmitter MUST drop whole frames only, |
| 269 | based on the size of the last transmitted frame, |
| 270 | to ensure successive RTP timestamps differ by a multiple of 120 and |
| 271 | to allow the receiver to use whole frames for concealment. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 272 | </t> |
| 273 | |
| 274 | <t> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 275 | DTX can be used with both variable and constant bitrate. |
| 276 | It will have a slightly lower speech or audio |
| 277 | quality than continuous transmission. Therefore, using continuous |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 278 | transmission is RECOMMENDED unless constraints on available network bandwidth |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 279 | are severe. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 280 | </t> |
| 281 | |
| 282 | </section> |
| 283 | |
| 284 | </section> |
| 285 | |
| 286 | <section title='Complexity'> |
| 287 | |
| 288 | <t> |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 289 | Complexity of the encoder can be scaled to optimize for CPU resources in real-time, mostly as |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 290 | a trade-off between audio quality and bitrate. Also, different modes of Opus have different complexity. |
| 291 | </t> |
| 292 | |
| 293 | </section> |
| 294 | |
| 295 | <section title="Forward Error Correction (FEC)"> |
| 296 | |
| 297 | <t> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 298 | The voice mode of Opus allows for embedding "in-band" forward error correction (FEC) |
| 299 | data into the Opus bit stream. This FEC scheme adds |
| 300 | redundant information about the previous packet (N-1) to the current |
| 301 | output packet N. For |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 302 | each frame, the encoder decides whether to use FEC based on (1) an |
| 303 | externally-provided estimate of the channel's packet loss rate; (2) an |
| 304 | externally-provided estimate of the channel's capacity; (3) the |
| 305 | sensitivity of the audio or speech signal to packet loss; (4) whether |
| 306 | the receiving decoder has indicated it can take advantage of "in-band" |
| 307 | FEC information. The decision to send "in-band" FEC information is |
| 308 | entirely controlled by the encoder and therefore no special precautions |
| 309 | for the payload have to be taken. |
| 310 | </t> |
| 311 | |
| 312 | <t> |
| 313 | On the receiving side, the decoder can take advantage of this |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 314 | additional information when it loses a packet and the next packet |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 315 | is available. In order to use the FEC data, the jitter buffer needs |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 316 | to provide access to payloads with the FEC data. |
| 317 | Instead of performing loss concealment for a missing packet, the |
| 318 | receiver can then configure its decoder to decode the FEC data from the next packet. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 319 | </t> |
| 320 | |
| 321 | <t> |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 322 | Any compliant Opus decoder is capable of ignoring |
| 323 | FEC information when it is not needed, so encoding with FEC cannot cause |
| 324 | interoperability problems. |
| 325 | However, if FEC cannot be used on the receiving side, then FEC |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 326 | SHOULD NOT be used, as it leads to an inefficient usage of network |
| 327 | resources. Decoder support for FEC SHOULD be indicated at the time a |
| 328 | session is set up. |
| 329 | </t> |
| 330 | |
| 331 | </section> |
| 332 | |
| 333 | <section title='Stereo Operation'> |
| 334 | |
| 335 | <t> |
| 336 | Opus allows for transmission of stereo audio signals. This operation |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 337 | is signaled in-band in the Opus bit-stream and no special arrangement |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 338 | is needed in the payload format. An |
| 339 | Opus decoder is capable of handling a stereo encoding, but an |
| 340 | application might only be capable of consuming a single audio |
| 341 | channel. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 342 | </t> |
| 343 | <t> |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 344 | If a decoder cannot take advantage of the benefits of a stereo signal |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 345 | this SHOULD be indicated at the time a session is set up. In that case |
| 346 | the sending side SHOULD NOT send stereo signals as it leads to an |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 347 | inefficient usage of network resources. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 348 | </t> |
| 349 | |
| 350 | </section> |
| 351 | |
| 352 | </section> |
| 353 | |
| 354 | <section title='Opus RTP Payload Format' anchor='opus-rtp-payload-format'> |
| 355 | <t>The payload format for Opus consists of the RTP header and Opus payload |
| 356 | data.</t> |
| 357 | <section title='RTP Header Usage'> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 358 | <t>The format of the RTP header is specified in <xref target="RFC3550"/>. |
| 359 | The use of the fields of the RTP header by the Opus payload format is |
| 360 | consistent with that specification.</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 361 | |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 362 | <t>The payload length of Opus is an integer number of octets and |
| 363 | therefore no padding is necessary. The payload MAY be padded by an |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 364 | integer number of octets according to <xref target="RFC3550"/>, |
| 365 | although the Opus internal padding is preferred.</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 366 | |
Jean-Marc Valin | f3d6c7a | 2014-06-30 14:13:46 -0400 | [diff] [blame] | 367 | <t>The timestamp, sequence number, and marker bit (M) of the RTP header |
| 368 | are used in accordance with Section 4.1 |
| 369 | of <xref target="RFC3551"/>.</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 370 | |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 371 | <t>The RTP payload type for Opus is to be assigned dynamically.</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 372 | |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 373 | <t>The receiving side MUST be prepared to receive duplicate RTP |
Jean-Marc Valin | 741ced3 | 2014-07-30 14:54:59 -0400 | [diff] [blame] | 374 | packets. The receiver MUST provide at most one of those payloads to the |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 375 | Opus decoder for decoding, and MUST discard the others.</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 376 | |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 377 | <t>Opus supports 5 different audio bandwidths, which can be adjusted during |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 378 | a stream. |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 379 | The RTP timestamp is incremented with a 48000 Hz clock rate |
| 380 | for all modes of Opus and all sampling rates. |
| 381 | The unit |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 382 | for the timestamp is samples per single (mono) channel. The RTP timestamp corresponds to the |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 383 | sample time of the first encoded sample in the encoded frame. |
| 384 | For data encoded with sampling rates other than 48000 Hz, |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 385 | the sampling rate has to be adjusted to 48000 Hz.</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 386 | |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 387 | </section> |
| 388 | |
| 389 | <section title='Payload Structure'> |
| 390 | <t> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 391 | The Opus encoder can output encoded frames representing 2.5, 5, 10, 20, |
| 392 | 40, or 60 ms of speech or audio data. Further, an arbitrary number of frames can be |
| 393 | combined into a packet, up to a maximum packet duration representing |
Timothy B. Terriberry | 1e87fea | 2014-07-25 22:33:55 -0700 | [diff] [blame] | 394 | 120 ms of speech or audio data. The grouping of one or more Opus |
| 395 | frames into a single Opus packet is defined in Section 3 of |
| 396 | <xref target="RFC6716"/>. An RTP payload MUST contain exactly one |
| 397 | Opus packet as defined by that document. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 398 | </t> |
| 399 | |
| 400 | <t><xref target='payload-structure'/> shows the structure combined with the RTP header.</t> |
| 401 | |
| 402 | <figure anchor="payload-structure" |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 403 | title="Packet structure with RTP header"> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 404 | <artwork align="center"> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 405 | <![CDATA[ |
| 406 | +----------+--------------+ |
| 407 | |RTP Header| Opus Payload | |
| 408 | +----------+--------------+ |
| 409 | ]]> |
| 410 | </artwork> |
| 411 | </figure> |
| 412 | |
| 413 | <t> |
Timothy B. Terriberry | 554b349 | 2014-10-03 21:49:57 -0700 | [diff] [blame] | 414 | <xref target='opus-packetization'/> shows supported frame sizes in |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 415 | milliseconds of encoded speech or audio data for the speech and audio modes |
| 416 | (Mode) and sampling rates (fs) of Opus and shows how the timestamp is |
| 417 | incremented for packetization (ts incr). If the Opus encoder |
| 418 | outputs multiple encoded frames into a single packet, the timestamp |
| 419 | increment is the sum of the increments for the individual frames. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 420 | </t> |
| 421 | |
Timothy B. Terriberry | 554b349 | 2014-10-03 21:49:57 -0700 | [diff] [blame] | 422 | <texttable anchor='opus-packetization' title="Supported Opus frame |
Jean-Marc Valin | 66611f1 | 2015-01-13 09:19:24 -0500 | [diff] [blame] | 423 | sizes and timestamp increments marked with an o. Unsupported marked with an x."> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 424 | <ttcol align='center'>Mode</ttcol> |
| 425 | <ttcol align='center'>fs</ttcol> |
| 426 | <ttcol align='center'>2.5</ttcol> |
| 427 | <ttcol align='center'>5</ttcol> |
| 428 | <ttcol align='center'>10</ttcol> |
| 429 | <ttcol align='center'>20</ttcol> |
| 430 | <ttcol align='center'>40</ttcol> |
| 431 | <ttcol align='center'>60</ttcol> |
| 432 | <c>ts incr</c> |
| 433 | <c>all</c> |
| 434 | <c>120</c> |
| 435 | <c>240</c> |
| 436 | <c>480</c> |
| 437 | <c>960</c> |
| 438 | <c>1920</c> |
| 439 | <c>2880</c> |
| 440 | <c>voice</c> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 441 | <c>NB/MB/WB/SWB/FB</c> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 442 | <c>x</c> |
| 443 | <c>x</c> |
Jean-Marc Valin | 66611f1 | 2015-01-13 09:19:24 -0500 | [diff] [blame] | 444 | <c>o</c> |
| 445 | <c>o</c> |
| 446 | <c>o</c> |
| 447 | <c>o</c> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 448 | <c>audio</c> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 449 | <c>NB/WB/SWB/FB</c> |
Jean-Marc Valin | 66611f1 | 2015-01-13 09:19:24 -0500 | [diff] [blame] | 450 | <c>o</c> |
| 451 | <c>o</c> |
| 452 | <c>o</c> |
| 453 | <c>o</c> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 454 | <c>x</c> |
| 455 | <c>x</c> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 456 | </texttable> |
| 457 | |
| 458 | </section> |
| 459 | |
| 460 | </section> |
| 461 | |
| 462 | <section title='Congestion Control'> |
| 463 | |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 464 | <t>The target bitrate of Opus can be adjusted at any point in time, thus |
| 465 | allowing efficient congestion control. Furthermore, the amount |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 466 | of encoded speech or audio data encoded in a |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 467 | single packet can be used for congestion control, since the transmission |
| 468 | rate is inversely proportional to the packet duration. A lower packet |
| 469 | transmission rate reduces the amount of header overhead, but at the same |
| 470 | time increases latency and loss sensitivity, so it ought to be used with |
| 471 | care.</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 472 | |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 473 | <t>Since UDP does not provide congestion control, applications that use |
| 474 | RTP over UDP SHOULD implement their own congestion control above the |
Jean-Marc Valin | 5b20cb0 | 2015-04-21 20:33:42 -0400 | [diff] [blame] | 475 | UDP layer <xref target="RFC5405"/>. Work in the rmcat working group |
| 476 | <xref target="rmcat"/> describes the |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 477 | interactions and conceptual interfaces necessary between the application |
| 478 | components that relate to congestion control, including the RTP layer, |
| 479 | the higher-level media codec control layer, and the lower-level |
| 480 | transport interface, as well as components dedicated to congestion |
| 481 | control functions.</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 482 | </section> |
| 483 | |
| 484 | <section title='IANA Considerations'> |
| 485 | <t>One media subtype (audio/opus) has been defined and registered as |
| 486 | described in the following section.</t> |
| 487 | |
| 488 | <section title='Opus Media Type Registration'> |
| 489 | <t>Media type registration is done according to <xref |
Jean-Marc Valin | d10755e | 2014-11-19 11:07:50 -0500 | [diff] [blame] | 490 | target="RFC6838"/> and <xref target="RFC4855"/>.<vspace |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 491 | blankLines='1'/></t> |
| 492 | |
| 493 | <t>Type name: audio<vspace blankLines='1'/></t> |
| 494 | <t>Subtype name: opus<vspace blankLines='1'/></t> |
| 495 | |
| 496 | <t>Required parameters:</t> |
| 497 | <t><list style="hanging"> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 498 | <t hangText="rate:"> the RTP timestamp is incremented with a |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 499 | 48000 Hz clock rate for all modes of Opus and all sampling |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 500 | rates. For data encoded with sampling rates other than 48000 Hz, |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 501 | the sampling rate has to be adjusted to 48000 Hz. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 502 | </t> |
| 503 | </list></t> |
| 504 | |
| 505 | <t>Optional parameters:</t> |
| 506 | |
| 507 | <t><list style="hanging"> |
Jean-Marc Valin | f22af9c | 2012-11-12 15:44:52 -0500 | [diff] [blame] | 508 | <t hangText="maxplaybackrate:"> |
| 509 | a hint about the maximum output sampling rate that the receiver is |
Jean-Marc Valin | acf0675 | 2012-11-22 17:10:50 -0500 | [diff] [blame] | 510 | capable of rendering in Hz. |
Jean-Marc Valin | f22af9c | 2012-11-12 15:44:52 -0500 | [diff] [blame] | 511 | The decoder MUST be capable of decoding |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 512 | any audio bandwidth but due to hardware limitations only signals |
Jean-Marc Valin | f22af9c | 2012-11-12 15:44:52 -0500 | [diff] [blame] | 513 | up to the specified sampling rate can be played back. Sending signals |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 514 | with higher audio bandwidth results in higher than necessary network |
| 515 | usage and encoding complexity, so an encoder SHOULD NOT encode |
Jean-Marc Valin | f22af9c | 2012-11-12 15:44:52 -0500 | [diff] [blame] | 516 | frequencies above the audio bandwidth specified by maxplaybackrate. |
| 517 | This parameter can take any value between 8000 and 48000, although |
Timothy B. Terriberry | 554b349 | 2014-10-03 21:49:57 -0700 | [diff] [blame] | 518 | commonly the value will match one of the Opus bandwidths |
Jean-Marc Valin | f22af9c | 2012-11-12 15:44:52 -0500 | [diff] [blame] | 519 | (<xref target="bandwidth_definitions"/>). |
| 520 | By default, the receiver is assumed to have no limitations, i.e. 48000. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 521 | <vspace blankLines='1'/> |
| 522 | </t> |
| 523 | |
Jean-Marc Valin | f22af9c | 2012-11-12 15:44:52 -0500 | [diff] [blame] | 524 | <t hangText="sprop-maxcapturerate:"> |
| 525 | a hint about the maximum input sampling rate that the sender is likely to produce. |
| 526 | This is not a guarantee that the sender will never send any higher bandwidth |
| 527 | (e.g. it could send a pre-recorded prompt that uses a higher bandwidth), but it |
| 528 | indicates to the receiver that frequencies above this maximum can safely be discarded. |
| 529 | This parameter is useful to avoid wasting receiver resources by operating the audio |
| 530 | processing pipeline (e.g. echo cancellation) at a higher rate than necessary. |
| 531 | This parameter can take any value between 8000 and 48000, although |
Timothy B. Terriberry | 554b349 | 2014-10-03 21:49:57 -0700 | [diff] [blame] | 532 | commonly the value will match one of the Opus bandwidths |
Jean-Marc Valin | f22af9c | 2012-11-12 15:44:52 -0500 | [diff] [blame] | 533 | (<xref target="bandwidth_definitions"/>). |
| 534 | By default, the sender is assumed to have no limitations, i.e. 48000. |
Jean-Marc Valin | 57fa056 | 2012-11-09 14:30:25 -0500 | [diff] [blame] | 535 | <vspace blankLines='1'/> |
| 536 | </t> |
| 537 | |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 538 | <t hangText="maxptime:"> the maximum duration of media represented |
| 539 | by a packet (according to Section 6 of |
| 540 | <xref target="RFC4566"/>) that a decoder wants to receive, in |
| 541 | milliseconds rounded up to the next full integer value. |
| 542 | Possible values are 3, 5, 10, 20, 40, 60, or an arbitrary |
| 543 | multiple of an Opus frame size rounded up to the next full integer |
| 544 | value, up to a maximum value of 120, as |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 545 | defined in <xref target='opus-rtp-payload-format'/>. If no value is |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 546 | specified, the default is 120. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 547 | <vspace blankLines='1'/></t> |
| 548 | |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 549 | <t hangText="ptime:"> the preferred duration of media represented |
| 550 | by a packet (according to Section 6 of |
| 551 | <xref target="RFC4566"/>) that a decoder wants to receive, in |
| 552 | milliseconds rounded up to the next full integer value. |
| 553 | Possible values are 3, 5, 10, 20, 40, 60, or an arbitrary |
| 554 | multiple of an Opus frame size rounded up to the next full integer |
| 555 | value, up to a maximum value of 120, as defined in <xref |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 556 | target='opus-rtp-payload-format'/>. If no value is |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 557 | specified, the default is 20. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 558 | <vspace blankLines='1'/></t> |
| 559 | |
Jean-Marc Valin | 65fb456 | 2015-01-06 02:35:31 -0500 | [diff] [blame] | 560 | <t hangText="maxaveragebitrate:"> specifies the maximum average |
| 561 | receive bitrate of a session in bits per second (b/s). The actual |
| 562 | value of the bitrate can vary, as it is dependent on the |
| 563 | characteristics of the media in a packet. Note that the maximum |
| 564 | average bitrate MAY be modified dynamically during a session. Any |
| 565 | positive integer is allowed, but values outside the range |
| 566 | 6000 to 510000 SHOULD be ignored. If no value is specified, the |
| 567 | maximum value specified in <xref target='bitrate_by_bandwidth'/> |
| 568 | for the corresponding mode of Opus and corresponding maxplaybackrate |
| 569 | is the default.<vspace blankLines='1'/></t> |
| 570 | |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 571 | <t hangText="stereo:"> |
| 572 | specifies whether the decoder prefers receiving stereo or mono signals. |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 573 | Possible values are 1 and 0 where 1 specifies that stereo signals are preferred, |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 574 | and 0 specifies that only mono signals are preferred. |
| 575 | Independent of the stereo parameter every receiver MUST be able to receive and |
| 576 | decode stereo signals but sending stereo signals to a receiver that signaled a |
| 577 | preference for mono signals may result in higher than necessary network |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 578 | utilization and encoding complexity. If no value is specified, |
| 579 | the default is 0 (mono).<vspace blankLines='1'/> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 580 | </t> |
| 581 | |
Jean-Marc Valin | 57fa056 | 2012-11-09 14:30:25 -0500 | [diff] [blame] | 582 | <t hangText="sprop-stereo:"> |
| 583 | specifies whether the sender is likely to produce stereo audio. |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 584 | Possible values are 1 and 0, where 1 specifies that stereo signals are likely to |
| 585 | be sent, and 0 specifies that the sender will likely only send mono. |
| 586 | This is not a guarantee that the sender will never send stereo audio |
| 587 | (e.g. it could send a pre-recorded prompt that uses stereo), but it |
| 588 | indicates to the receiver that the received signal can be safely downmixed to mono. |
| 589 | This parameter is useful to avoid wasting receiver resources by operating the audio |
| 590 | processing pipeline (e.g. echo cancellation) in stereo when not necessary. |
| 591 | If no value is specified, the default is 0 |
| 592 | (mono).<vspace blankLines='1'/> |
Jean-Marc Valin | 57fa056 | 2012-11-09 14:30:25 -0500 | [diff] [blame] | 593 | </t> |
| 594 | |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 595 | <t hangText="cbr:"> |
| 596 | specifies if the decoder prefers the use of a constant bitrate versus |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 597 | variable bitrate. Possible values are 1 and 0, where 1 specifies constant |
| 598 | bitrate and 0 specifies variable bitrate. If no value is specified, |
| 599 | the default is 0 (vbr). When cbr is 1, the maximum average bitrate can still |
| 600 | change, e.g. to adapt to changing network conditions.<vspace blankLines='1'/> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 601 | </t> |
| 602 | |
Jean-Marc Valin | 15f0f1f | 2012-11-29 09:24:54 -0500 | [diff] [blame] | 603 | <t hangText="useinbandfec:"> specifies that the decoder has the capability to |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 604 | take advantage of the Opus in-band FEC. Possible values are 1 and 0. |
| 605 | Providing 0 when FEC cannot be used on the receiving side is |
| 606 | RECOMMENDED. If no |
Julian Spittka | 03d5fec | 2012-11-30 03:12:59 -0500 | [diff] [blame] | 607 | value is specified, useinbandfec is assumed to be 0. |
Jean-Marc Valin | 15f0f1f | 2012-11-29 09:24:54 -0500 | [diff] [blame] | 608 | This parameter is only a preference and the receiver MUST be able to process |
Julian Spittka | 03d5fec | 2012-11-30 03:12:59 -0500 | [diff] [blame] | 609 | packets that include FEC information, even if it means the FEC part is discarded. |
Jean-Marc Valin | 15f0f1f | 2012-11-29 09:24:54 -0500 | [diff] [blame] | 610 | <vspace blankLines='1'/></t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 611 | |
| 612 | <t hangText="usedtx:"> specifies if the decoder prefers the use of |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 613 | DTX. Possible values are 1 and 0. If no value is specified, the |
| 614 | default is 0.<vspace blankLines='1'/></t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 615 | </list></t> |
| 616 | |
| 617 | <t>Encoding considerations:<vspace blankLines='1'/></t> |
| 618 | <t><list style="hanging"> |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 619 | <t>The Opus media type is framed and consists of binary data according |
Jean-Marc Valin | d10755e | 2014-11-19 11:07:50 -0500 | [diff] [blame] | 620 | to Section 4.8 in <xref target="RFC6838"/>.</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 621 | </list></t> |
| 622 | |
| 623 | <t>Security considerations: </t> |
| 624 | <t><list style="hanging"> |
| 625 | <t>See <xref target='security-considerations'/> of this document.</t> |
| 626 | </list></t> |
| 627 | |
| 628 | <t>Interoperability considerations: none<vspace blankLines='1'/></t> |
Jean-Marc Valin | 66611f1 | 2015-01-13 09:19:24 -0500 | [diff] [blame] | 629 | <t>Published specification: RFC [XXXX]</t> |
| 630 | <t>Note to the RFC Editor: Replace [XXXX] with the number of the published |
| 631 | RFC.<vspace blankLines='1'/></t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 632 | |
| 633 | <t>Applications that use this media type: </t> |
| 634 | <t><list style="hanging"> |
| 635 | <t>Any application that requires the transport of |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 636 | speech or audio data can use this media type. Some examples are, |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 637 | but not limited to, audio and video conferencing, Voice over IP, |
| 638 | media streaming.</t> |
| 639 | </list></t> |
| 640 | |
Jean-Marc Valin | 66611f1 | 2015-01-13 09:19:24 -0500 | [diff] [blame] | 641 | <t>Fragment identifier considerations: N/A<vspace blankLines='1'/></t> |
| 642 | |
Jean-Marc Valin | 5771b5a | 2013-08-02 12:04:50 -0400 | [diff] [blame] | 643 | <t>Person & email address to contact for further information:</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 644 | <t><list style="hanging"> |
| 645 | <t>SILK Support silksupport@skype.net</t> |
| 646 | <t>Jean-Marc Valin jmvalin@jmvalin.ca</t> |
| 647 | </list></t> |
| 648 | |
| 649 | <t>Intended usage: COMMON<vspace blankLines='1'/></t> |
| 650 | |
| 651 | <t>Restrictions on usage:<vspace blankLines='1'/></t> |
| 652 | |
| 653 | <t><list style="hanging"> |
| 654 | <t>For transfer over RTP, the RTP payload format (<xref |
| 655 | target='opus-rtp-payload-format'/> of this document) SHALL be |
| 656 | used.</t> |
| 657 | </list></t> |
| 658 | |
| 659 | <t>Author:</t> |
| 660 | <t><list style="hanging"> |
Julian Spittka | 03d5fec | 2012-11-30 03:12:59 -0500 | [diff] [blame] | 661 | <t>Julian Spittka jspittka@gmail.com<vspace blankLines='1'/></t> |
| 662 | <t>Koen Vos koenvos74@gmail.com<vspace blankLines='1'/></t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 663 | <t>Jean-Marc Valin jmvalin@jmvalin.ca<vspace blankLines='1'/></t> |
| 664 | </list></t> |
| 665 | |
Jean-Marc Valin | 66611f1 | 2015-01-13 09:19:24 -0500 | [diff] [blame] | 666 | <t> Change controller: IETF Payload Working Group delegated from the IESG</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 667 | </section> |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 668 | </section> |
| 669 | |
| 670 | <section title='SDP Considerations'> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 671 | <t>The information described in the media type specification has a |
| 672 | specific mapping to fields in the Session Description Protocol (SDP) |
| 673 | <xref target="RFC4566"/>, which is commonly used to describe RTP |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 674 | sessions. When SDP is used to specify sessions employing Opus, |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 675 | the mapping is as follows:</t> |
| 676 | |
| 677 | <t> |
| 678 | <list style="symbols"> |
| 679 | <t>The media type ("audio") goes in SDP "m=" as the media name.</t> |
| 680 | |
| 681 | <t>The media subtype ("opus") goes in SDP "a=rtpmap" as the encoding |
Jean-Marc Valin | 57fa056 | 2012-11-09 14:30:25 -0500 | [diff] [blame] | 682 | name. The RTP clock rate in "a=rtpmap" MUST be 48000 and the number of |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 683 | channels MUST be 2.</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 684 | |
Timothy B. Terriberry | 239e9a3 | 2012-11-21 18:48:09 -0800 | [diff] [blame] | 685 | <t>The OPTIONAL media type parameters "ptime" and "maxptime" are |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 686 | mapped to "a=ptime" and "a=maxptime" attributes, respectively, in the |
| 687 | SDP.</t> |
| 688 | |
Jean-Marc Valin | 65fb456 | 2015-01-06 02:35:31 -0500 | [diff] [blame] | 689 | <t>The OPTIONAL media type parameters "maxaveragebitrate", |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 690 | "maxplaybackrate", "stereo", "cbr", "useinbandfec", and |
Timothy B. Terriberry | 554b349 | 2014-10-03 21:49:57 -0700 | [diff] [blame] | 691 | "usedtx", when present, MUST be included in the "a=fmtp" attribute |
Julian Spittka | 03d5fec | 2012-11-30 03:12:59 -0500 | [diff] [blame] | 692 | in the SDP, expressed as a media type string in the form of a |
Timothy B. Terriberry | 239e9a3 | 2012-11-21 18:48:09 -0800 | [diff] [blame] | 693 | semicolon-separated list of parameter=value pairs (e.g., |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 694 | maxplaybackrate=48000). They MUST NOT be specified in an |
Timothy B. Terriberry | f92c87a | 2012-11-22 04:38:35 -0800 | [diff] [blame] | 695 | SSRC-specific "fmtp" source-level attribute (as defined in |
| 696 | Section 6.3 of <xref target="RFC5576"/>).</t> |
Timothy B. Terriberry | 239e9a3 | 2012-11-21 18:48:09 -0800 | [diff] [blame] | 697 | |
| 698 | <t>The OPTIONAL media type parameters "sprop-maxcapturerate", |
| 699 | and "sprop-stereo" MAY be mapped to the "a=fmtp" SDP attribute by |
| 700 | copying them directly from the media type parameter string as part |
| 701 | of the semicolon-separated list of parameter=value pairs (e.g., |
| 702 | sprop-stereo=1). These same OPTIONAL media type parameters MAY also |
Timothy B. Terriberry | f92c87a | 2012-11-22 04:38:35 -0800 | [diff] [blame] | 703 | be specified using an SSRC-specific "fmtp" source-level attribute |
| 704 | as described in Section 6.3 of <xref target="RFC5576"/>. |
| 705 | They MAY be specified in both places, in which case the parameter |
| 706 | in the source-level attribute overrides the one found on the |
| 707 | "a=fmtp" line. The value of any parameter which is not specified in |
| 708 | a source-level source attribute MUST be taken from the "a=fmtp" |
| 709 | line, if it is present there.</t> |
Timothy B. Terriberry | 239e9a3 | 2012-11-21 18:48:09 -0800 | [diff] [blame] | 710 | |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 711 | </list> |
| 712 | </t> |
| 713 | |
| 714 | <t>Below are some examples of SDP session descriptions for Opus:</t> |
| 715 | |
Jean-Marc Valin | acf0675 | 2012-11-22 17:10:50 -0500 | [diff] [blame] | 716 | <t>Example 1: Standard mono session with 48000 Hz clock rate</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 717 | <figure> |
| 718 | <artwork> |
| 719 | <![CDATA[ |
| 720 | m=audio 54312 RTP/AVP 101 |
Jean-Marc Valin | 57fa056 | 2012-11-09 14:30:25 -0500 | [diff] [blame] | 721 | a=rtpmap:101 opus/48000/2 |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 722 | ]]> |
| 723 | </artwork> |
| 724 | </figure> |
| 725 | |
| 726 | |
| 727 | <t>Example 2: 16000 Hz clock rate, maximum packet size of 40 ms, |
| 728 | recommended packet size of 40 ms, maximum average bitrate of 20000 bps, |
Jean-Marc Valin | e070300 | 2014-07-30 13:41:28 -0400 | [diff] [blame] | 729 | prefers to receive stereo but only plans to send mono, FEC is desired, |
Jean-Marc Valin | 6b3d5c8 | 2014-06-30 17:13:16 -0400 | [diff] [blame] | 730 | DTX is not desired</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 731 | |
| 732 | <figure> |
| 733 | <artwork> |
| 734 | <![CDATA[ |
| 735 | m=audio 54312 RTP/AVP 101 |
Jean-Marc Valin | 57fa056 | 2012-11-09 14:30:25 -0500 | [diff] [blame] | 736 | a=rtpmap:101 opus/48000/2 |
Jean-Marc Valin | acf0675 | 2012-11-22 17:10:50 -0500 | [diff] [blame] | 737 | a=fmtp:101 maxplaybackrate=16000; sprop-maxcapturerate=16000; |
Jean-Marc Valin | 65fb456 | 2015-01-06 02:35:31 -0500 | [diff] [blame] | 738 | maxaveragebitrate=20000; stereo=1; useinbandfec=1; usedtx=0 |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 739 | a=ptime:40 |
| 740 | a=maxptime:40 |
| 741 | ]]> |
| 742 | </artwork> |
| 743 | </figure> |
| 744 | |
Jean-Marc Valin | acf0675 | 2012-11-22 17:10:50 -0500 | [diff] [blame] | 745 | <t>Example 3: Two-way full-band stereo preferred</t> |
| 746 | |
| 747 | <figure> |
| 748 | <artwork> |
| 749 | <![CDATA[ |
| 750 | m=audio 54312 RTP/AVP 101 |
| 751 | a=rtpmap:101 opus/48000/2 |
| 752 | a=fmtp:101 stereo=1; sprop-stereo=1 |
| 753 | ]]> |
| 754 | </artwork> |
| 755 | </figure> |
| 756 | |
| 757 | |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 758 | <section title='SDP Offer/Answer Considerations'> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 759 | |
| 760 | <t>When using the offer-answer procedure described in <xref |
| 761 | target="RFC3264"/> to negotiate the use of Opus, the following |
| 762 | considerations apply:</t> |
| 763 | |
| 764 | <t><list style="symbols"> |
| 765 | |
| 766 | <t>Opus supports several clock rates. For signaling purposes only |
| 767 | the highest, i.e. 48000, is used. The actual clock rate of the |
| 768 | corresponding media is signaled inside the payload and is not |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 769 | restricted by this payload format description. The decoder MUST be |
| 770 | capable of decoding every received clock rate. An example |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 771 | is shown below: |
| 772 | |
| 773 | <figure> |
| 774 | <artwork> |
| 775 | <![CDATA[ |
Jean-Marc Valin | 57fa056 | 2012-11-09 14:30:25 -0500 | [diff] [blame] | 776 | m=audio 54312 RTP/AVP 100 |
| 777 | a=rtpmap:100 opus/48000/2 |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 778 | ]]> |
| 779 | </artwork> |
| 780 | </figure> |
| 781 | </t> |
| 782 | |
Jean-Marc Valin | acf0675 | 2012-11-22 17:10:50 -0500 | [diff] [blame] | 783 | <t>The "ptime" and "maxptime" parameters are unidirectional |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 784 | receive-only parameters and typically will not compromise |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 785 | interoperability; however, some values might cause application |
| 786 | performance to suffer. <xref |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 787 | target="RFC3264"/> defines the SDP offer-answer handling of the |
| 788 | "ptime" parameter. The "maxptime" parameter MUST be handled in the |
| 789 | same way.</t> |
| 790 | |
| 791 | <t> |
Jean-Marc Valin | acf0675 | 2012-11-22 17:10:50 -0500 | [diff] [blame] | 792 | The "maxplaybackrate" parameter is a unidirectional receive-only |
Timothy B. Terriberry | 1e87fea | 2014-07-25 22:33:55 -0700 | [diff] [blame] | 793 | parameter that reflects limitations of the local receiver. When |
| 794 | sending to a single destination, a sender MUST NOT use an audio |
Jean-Marc Valin | 741ced3 | 2014-07-30 14:54:59 -0400 | [diff] [blame] | 795 | bandwidth higher than necessary to make full use of audio sampled at |
Timothy B. Terriberry | 1e87fea | 2014-07-25 22:33:55 -0700 | [diff] [blame] | 796 | a sampling rate of "maxplaybackrate". Gateways or senders that |
| 797 | are sending the same encoded audio to multiple destinations |
| 798 | SHOULD NOT use an audio bandwidth higher than necessary to |
| 799 | represent audio sampled at "maxplaybackrate", as this would lead |
| 800 | to inefficient use of network resources. |
Jean-Marc Valin | f22af9c | 2012-11-12 15:44:52 -0500 | [diff] [blame] | 801 | The "maxplaybackrate" parameter does not |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 802 | affect interoperability. Also, this parameter SHOULD NOT be used |
| 803 | to adjust the audio bandwidth as a function of the bitrate, as this |
| 804 | is the responsibility of the Opus encoder implementation. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 805 | </t> |
| 806 | |
Jean-Marc Valin | 65fb456 | 2015-01-06 02:35:31 -0500 | [diff] [blame] | 807 | <t>The "maxaveragebitrate" parameter is a unidirectional receive-only |
| 808 | parameter that reflects limitations of the local receiver. The sender |
| 809 | of the other side MUST NOT send with an average bitrate higher than |
| 810 | "maxaveragebitrate" as it might overload the network and/or |
| 811 | receiver. The "maxaveragebitrate" parameter typically will not |
| 812 | compromise interoperability; however, some values might cause |
| 813 | application performance to suffer, and ought to be set with |
| 814 | care.</t> |
| 815 | |
Julian Spittka | 03d5fec | 2012-11-30 03:12:59 -0500 | [diff] [blame] | 816 | <t>The "sprop-maxcapturerate" and "sprop-stereo" parameters are |
Jean-Marc Valin | acf0675 | 2012-11-22 17:10:50 -0500 | [diff] [blame] | 817 | unidirectional sender-only parameters that reflect limitations of |
| 818 | the sender side. |
Jean-Marc Valin | b880e9b | 2012-11-22 17:25:22 -0500 | [diff] [blame] | 819 | They allow the receiver to set up a reduced-complexity audio |
| 820 | processing pipeline if the sender is not planning to use the full |
| 821 | range of Opus's capabilities. |
Julian Spittka | 03d5fec | 2012-11-30 03:12:59 -0500 | [diff] [blame] | 822 | Neither "sprop-maxcapturerate" nor "sprop-stereo" affect |
Jean-Marc Valin | acf0675 | 2012-11-22 17:10:50 -0500 | [diff] [blame] | 823 | interoperability and the receiver MUST be capable of receiving any signal. |
| 824 | </t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 825 | |
| 826 | <t> |
Jean-Marc Valin | 57fa056 | 2012-11-09 14:30:25 -0500 | [diff] [blame] | 827 | The "stereo" parameter is a unidirectional receive-only |
Timothy B. Terriberry | 1e87fea | 2014-07-25 22:33:55 -0700 | [diff] [blame] | 828 | parameter. When sending to a single destination, a sender MUST |
| 829 | NOT use stereo when "stereo" is 0. Gateways or senders that are |
| 830 | sending the same encoded audio to multiple destinations SHOULD |
| 831 | NOT use stereo when "stereo" is 0, as this would lead to |
| 832 | inefficient use of network resources. The "stereo" parameter does |
| 833 | not affect interoperability. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 834 | </t> |
| 835 | |
| 836 | <t> |
Jean-Marc Valin | 57fa056 | 2012-11-09 14:30:25 -0500 | [diff] [blame] | 837 | The "cbr" parameter is a unidirectional receive-only |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 838 | parameter. |
| 839 | </t> |
| 840 | |
Jean-Marc Valin | 57fa056 | 2012-11-09 14:30:25 -0500 | [diff] [blame] | 841 | <t>The "useinbandfec" parameter is a unidirectional receive-only |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 842 | parameter.</t> |
| 843 | |
Jean-Marc Valin | 57fa056 | 2012-11-09 14:30:25 -0500 | [diff] [blame] | 844 | <t>The "usedtx" parameter is a unidirectional receive-only |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 845 | parameter.</t> |
| 846 | |
| 847 | <t>Any unknown parameter in an offer MUST be ignored by the receiver |
| 848 | and MUST be removed from the answer.</t> |
| 849 | |
| 850 | </list></t> |
Jean-Marc Valin | 155f99c | 2015-02-06 13:34:32 -0500 | [diff] [blame] | 851 | |
| 852 | <t> |
| 853 | The Opus parameters in an SDP Offer/Answer exchange are completely |
| 854 | orthogonal, and there is no relationship between the SDP Offer and |
| 855 | the Answer. |
| 856 | </t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 857 | </section> |
| 858 | |
| 859 | <section title='Declarative SDP Considerations for Opus'> |
| 860 | |
| 861 | <t>For declarative use of SDP such as in Session Announcement Protocol |
| 862 | (SAP), <xref target="RFC2974"/>, and RTSP, <xref target="RFC2326"/>, for |
| 863 | Opus, the following needs to be considered:</t> |
| 864 | |
| 865 | <t><list style="symbols"> |
| 866 | |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 867 | <t>The values for "maxptime", "ptime", "maxplaybackrate", and |
Jean-Marc Valin | 65fb456 | 2015-01-06 02:35:31 -0500 | [diff] [blame] | 868 | "maxaveragebitrate" ought to be selected carefully to ensure that a |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 869 | reasonable performance can be achieved for the participants of a session.</t> |
| 870 | |
| 871 | <t> |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 872 | The values for "maxptime", "ptime", and of the payload |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 873 | format configuration are recommendations by the decoding side to ensure |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 874 | the best performance for the decoder. |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 875 | </t> |
| 876 | |
| 877 | <t>All other parameters of the payload format configuration are declarative |
| 878 | and a participant MUST use the configurations that are provided for |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 879 | the session. More than one configuration can be provided if necessary |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 880 | by declaring multiple RTP payload types; however, the number of types |
Timothy B. Terriberry | f7faa90 | 2014-07-25 21:45:46 -0700 | [diff] [blame] | 881 | ought to be kept small.</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 882 | </list></t> |
| 883 | </section> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 884 | </section> |
| 885 | |
| 886 | <section title='Security Considerations' anchor='security-considerations'> |
| 887 | |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 888 | <t>Use of variable bitrate (VBR) is subject to the security considerations in |
| 889 | <xref target="RFC6562"/>.</t> |
| 890 | |
| 891 | <t>RTP packets using the payload format defined in this specification |
| 892 | are subject to the security considerations discussed in the RTP |
| 893 | specification <xref target="RFC3550"/>, and in any applicable RTP profile such as |
| 894 | RTP/AVP <xref target="RFC3551"/>, RTP/AVPF <xref target="RFC4585"/>, |
| 895 | RTP/SAVP <xref target="RFC3711"/> or RTP/SAVPF <xref target="RFC5124"/>. |
| 896 | However, as "Securing the RTP Protocol Framework: |
| 897 | Why RTP Does Not Mandate a Single Media Security Solution" |
Jean-Marc Valin | 51abf48 | 2015-04-14 20:50:28 -0400 | [diff] [blame] | 898 | <xref target="RFC7202"/> discusses, it is not an RTP payload |
| 899 | format's responsibility to discuss or mandate what solutions are used |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 900 | to meet the basic security goals like confidentiality, integrity and |
| 901 | source authenticity for RTP in general. This responsibility lays on |
| 902 | anyone using RTP in an application. They can find guidance on |
| 903 | available security mechanisms and important considerations in Options |
| 904 | for Securing RTP Sessions [I-D.ietf-avtcore-rtp-security-options]. |
| 905 | Applications SHOULD use one or more appropriate strong security |
| 906 | mechanisms.</t> |
| 907 | |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 908 | <t>This payload format and the Opus encoding do not exhibit any |
| 909 | significant non-uniformity in the receiver-end computational load and thus |
| 910 | are unlikely to pose a denial-of-service threat due to the receipt of |
| 911 | pathological datagrams.</t> |
| 912 | </section> |
| 913 | |
| 914 | <section title='Acknowledgements'> |
Jean-Marc Valin | 3b1928c | 2014-12-08 16:25:57 -0500 | [diff] [blame] | 915 | <t>Many people have made useful comments and suggestions contributing to this document. |
| 916 | In particular, we would like to thank |
| 917 | Tina le Grand, Cullen Jennings, Jonathan Lennox, Gregory Maxwell, Colin Perkins, Jan Skoglund, |
| 918 | Timothy B. Terriberry, Martin Thompson, Justin Uberti, Magnus Westerlund, and Mo Zanaty.</t> |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 919 | </section> |
| 920 | </middle> |
| 921 | |
| 922 | <back> |
| 923 | <references title="Normative References"> |
| 924 | &rfc2119; |
Jean-Marc Valin | f3d6c7a | 2014-06-30 14:13:46 -0400 | [diff] [blame] | 925 | &rfc3389; |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 926 | &rfc3550; |
| 927 | &rfc3711; |
| 928 | &rfc3551; |
Jean-Marc Valin | d10755e | 2014-11-19 11:07:50 -0500 | [diff] [blame] | 929 | &rfc6838; |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 930 | &rfc4855; |
| 931 | &rfc4566; |
| 932 | &rfc3264; |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 933 | &rfc2326; |
Timothy B. Terriberry | 239e9a3 | 2012-11-21 18:48:09 -0800 | [diff] [blame] | 934 | &rfc5576; |
Jean-Marc Valin | bdf8740 | 2012-07-11 15:54:55 -0400 | [diff] [blame] | 935 | &rfc6562; |
Jean-Marc Valin | acf0675 | 2012-11-22 17:10:50 -0500 | [diff] [blame] | 936 | &rfc6716; |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 937 | </references> |
| 938 | |
Jean-Marc Valin | d10755e | 2014-11-19 11:07:50 -0500 | [diff] [blame] | 939 | <references title="Informative References"> |
| 940 | &rfc2974; |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 941 | &rfc4585; |
| 942 | &rfc5124; |
Jean-Marc Valin | 5b20cb0 | 2015-04-21 20:33:42 -0400 | [diff] [blame] | 943 | &rfc5405; |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 944 | &rfc7202; |
| 945 | |
Jean-Marc Valin | 5b20cb0 | 2015-04-21 20:33:42 -0400 | [diff] [blame] | 946 | <reference anchor='rmcat' target='https://datatracker.ietf.org/wg/rmcat/documents/'> |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 947 | <front> |
Jean-Marc Valin | 5b20cb0 | 2015-04-21 20:33:42 -0400 | [diff] [blame] | 948 | <title>rmcat documents</title> |
| 949 | <author/> |
| 950 | <date/> |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 951 | <abstract> |
| 952 | <t></t> |
| 953 | </abstract></front> |
Jean-Marc Valin | 5771a67 | 2015-04-10 17:50:26 -0400 | [diff] [blame] | 954 | </reference> |
| 955 | |
| 956 | |
Jean-Marc Valin | d10755e | 2014-11-19 11:07:50 -0500 | [diff] [blame] | 957 | </references> |
| 958 | |
Gregory Maxwell | 0c90607 | 2012-06-19 09:11:40 -0400 | [diff] [blame] | 959 | </back> |
| 960 | </rfc> |