idnits 2.17.1 draft-romanow-clue-framework-01.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (October 3, 2011) is 4583 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- -- Obsolete informational reference (is this intentional?): RFC 5117 (Obsoleted by RFC 7667) Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 CLUE WG A. Romanow 3 Internet-Draft Cisco Systems 4 Intended status: Informational M. Duckworth 5 Expires: April 5, 2012 Polycom 6 A. Pepperell 7 B. Baldino 8 Cisco Systems 9 October 3, 2011 11 Framework for Telepresence Multi-Streams 12 draft-romanow-clue-framework-01.txt 14 Abstract 16 This memo offers a framework for a protocol that enables devices in a 17 telepresence conference to interoperate by specifying the 18 relationships between multiple RTP streams. 20 Status of this Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on April 5, 2012. 37 Copyright Notice 39 Copyright (c) 2011 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 55 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 56 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 5 57 4. Framework Features . . . . . . . . . . . . . . . . . . . . . . 7 58 5. Stream Information . . . . . . . . . . . . . . . . . . . . . . 8 59 5.1. Media capture -- Audio and Video . . . . . . . . . . . . . 9 60 5.2. Attributes . . . . . . . . . . . . . . . . . . . . . . . . 9 61 5.2.1. Purpose . . . . . . . . . . . . . . . . . . . . . . . 10 62 5.2.2. Audio mixed . . . . . . . . . . . . . . . . . . . . . 10 63 5.2.3. Audio Channel Format . . . . . . . . . . . . . . . . . 10 64 5.2.4. Area of capture . . . . . . . . . . . . . . . . . . . 11 65 5.2.5. Point of capture . . . . . . . . . . . . . . . . . . . 12 66 5.2.6. Area Scale Millimeters . . . . . . . . . . . . . . . . 12 67 5.2.7. Video composed . . . . . . . . . . . . . . . . . . . . 12 68 5.2.8. Auto-switched . . . . . . . . . . . . . . . . . . . . 12 69 5.3. Capture Set . . . . . . . . . . . . . . . . . . . . . . . 12 70 6. Choosing Streams . . . . . . . . . . . . . . . . . . . . . . . 14 71 6.1. Message Flow . . . . . . . . . . . . . . . . . . . . . . . 15 72 6.1.1. Provider Capabilities Announcement . . . . . . . . . . 15 73 6.1.2. Consumer Capability Message . . . . . . . . . . . . . 16 74 6.1.3. Consumer Configure Request . . . . . . . . . . . . . . 16 75 6.2. Physical Simultaneity . . . . . . . . . . . . . . . . . . 16 76 6.3. Encoding Groups . . . . . . . . . . . . . . . . . . . . . 18 77 6.3.1. Encoding Group Structure . . . . . . . . . . . . . . . 19 78 6.3.2. Individual Encodes . . . . . . . . . . . . . . . . . . 19 79 6.3.3. More on Encoding Groups . . . . . . . . . . . . . . . 20 80 6.3.4. Examples of Encoding Groups . . . . . . . . . . . . . 21 81 7. Using the Framework . . . . . . . . . . . . . . . . . . . . . 23 82 7.1. The MCU Case . . . . . . . . . . . . . . . . . . . . . . . 27 83 7.2. Media Consumer Behavior . . . . . . . . . . . . . . . . . 27 84 7.2.1. One screen consumer . . . . . . . . . . . . . . . . . 28 85 7.2.2. Two screen consumer configuring the example . . . . . 28 86 7.2.3. Three screen consumer configuring the example . . . . 29 87 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29 88 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 89 10. Security Considerations . . . . . . . . . . . . . . . . . . . 29 90 11. Informative References . . . . . . . . . . . . . . . . . . . . 29 91 Appendix A. Open Issues . . . . . . . . . . . . . . . . . . . . . 30 92 A.1. Video layout arrangements and centralized composition . . 30 93 A.2. Source is selectable . . . . . . . . . . . . . . . . . . . 30 94 A.3. Media Source Selection . . . . . . . . . . . . . . . . . . 30 95 A.4. Endpoint requesting many streams from MCU . . . . . . . . 31 96 A.5. VAD (voice activity detection) tagging of audio streams . 31 97 A.6. Private Information . . . . . . . . . . . . . . . . . . . 31 98 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 31 100 1. Introduction 102 Current telepresence systems, though based on open standards such as 103 RTP [RFC3550] and SIP [RFC3261], cannot easily interoperate with each 104 other. A major factor limiting the interoperability of telepresence 105 systems is the lack of a standardized way to describe and negotiate 106 the use of the multiple streams of audio and video comprising the 107 media flows. This draft provides a framework for a protocol to 108 enable interoperability by handling multiple streams in a 109 standardized way. It is intended to support the use cases described 110 in draft-ietf-clue-telepresence-use-cases-00 and to meet the 111 requirements in draft-romanow-clue-requirements-xx. 113 The solution described here is strongly focused on what is being done 114 today, rather than on a vision of future conferencing. At the same 115 time, the highest priority has been given to creating an extensible 116 framework to make it easy to accommodate future conferencing 117 functionality as it evolves. 119 The purpose of this effort is to make it possible to handle multiple 120 streams of media in such a way that a satisfactory user experience is 121 possible even when participants are on different vendor equipment and 122 when they are using devices with different types of communication 123 capabilities. Information about the relationship of media streams 124 must be communicated so that audio/video rendering can be done in the 125 best possible manner. In addition, it is necessary to choose which 126 media streams are sent. 128 There is no attempt here to dictate to the renderer what it should 129 do. What the renderer does is up to the renderer. 131 After the following Definitions, two short sections introduce key 132 concepts. The body of the text comprises three sections that deal 133 with in turn stream content, choosing streams and an implementation 134 example. The media provider and media consumer behavior are 135 described in separate sections as well. Several appendices describe 136 further details for using the framework. 138 2. Terminology 140 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 141 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 142 document are to be interpreted as described in RFC 2119 [RFC2119]. 144 3. Definitions 146 The definitions marked with an "*" are new; all the others are from 147 draft-wenger-clue-definitions-00-01.txt. 149 *Audio Capture: Media Capture for audio. Denoted as ACn. 151 Capture Device: A device that converts audio and video input into an 152 electrical signal, in most cases to be fed into a media encoder. 153 Cameras and microphones are examples for capture devices. 155 Capture Scene: the scene that is captured by a collection of Capture 156 Devices. A Capture Scene may be represented by more than one type of 157 Media. A Capture Scene may include more than one Media Capture of 158 the same type. An example of a Capture Scene is the video image of a 159 group of people seated next to each other, along with the sound of 160 their voices, which could be represented by some number of VCs and 161 ACs. A middle box may also express Capture Scenes that it constructs 162 from Media streams it receives. 164 A Capture Set includes Media Captures that all represent some aspect 165 of the same Capture Scene. The items (rows) in a Capture Set 166 represent different alternatives for representing the same Capture 167 Scene. 169 Conference: used as defined in [RFC4353], A Framework for 170 Conferencing within the Session Initiation Protocol (SIP). 172 Individual Encode: A variable with a set of attributes that describes 173 the maximum values of a single audio or video capture encoding. The 174 attributes include: maximum bandwidth- and for video maximum 175 macroblocks, maximum width, maximum height, maximum frame rate. 176 [Edt. These are based on H.264.] 178 *Encoding Group: Encoding group: A set of encoding parameters 179 representing a device's complete encoding capabilities or a 180 subdivision of them. Media stream providers formed of multiple 181 physical units, in each of which resides some encoding capability, 182 would typically advertise themselves to the remote media stream 183 consumer as being formed multiple encoding groups. Within each 184 encoding group, multiple potential actual encodings are possible, 185 with the sum of those encodings' characteristics constrained to being 186 less than or equal to the group-wide constraints. 188 Endpoint: The logical point of final termination through receiving, 189 decoding and rendering, and/or initiation through capturing, 190 encoding, and sending of media streams. An endpoint consists of one 191 or more physical devices which source and sink media streams, and 192 exactly one [RFC4353] Participant (which, in turn, includes exactly 193 one SIP User Agent). In contrast to an endpoint, an MCU may also 194 send and receive media streams, but it is not the initiator nor the 195 final terminator in the sense that Media is Captured or Rendered. 196 Endpoints can be anything from multiscreen/multicamera rooms to 197 handheld devices. 199 Endpoint Characteristics: include placement of Capture and Rendering 200 Devices, capture/render angle, resolution of cameras and screens, 201 spatial location and mixing parameters of microphones. Endpoint 202 characteristics are not specific to individual media streams sent by 203 the endpoint. 205 Left: For media captures, left and right is from the point of view of 206 a person observing the rendered media. 208 MCU: Multipoint Control Unit (MCU) - a device that connects two or 209 more endpoints together into one single multimedia conference 210 [RFC5117]. An MCU includes an [RFC4353] Mixer. [Edt. RFC4353 is 211 tardy in requiring that media from the mixer be sent to EACH 212 participant. I think we have practical use cases where this is not 213 the case. But the bug (if it is one) is in 4353 and not herein. 215 Media: Any data that, after suitable encoding, can be conveyed over 216 RTP, including audio, video or timed text. 218 *Media Capture: a source of Media, such as from one or more Capture 219 Devices. A Media Capture may be the source of one or more Media 220 streams. A Media Capture may also be constructed from other Media 221 streams. A middle box can express Media Captures that it constructs 222 from Media streams it receives. 224 *Media Consumer: an Endpoint or middle box that receives Media 225 streams 227 *Media Provider: an Endpoint or middle box that sends Media streams 229 Model: a set of assumptions a telepresence system of a given vendor 230 adheres to and expects the remote telepresence system(s) also to 231 adhere to. 233 Right: For media captures, left and right is from the point of view 234 of a person observing the rendered media. 236 Render: the process of generating a representation from a media, such 237 as displayed motion video or sound emitted from loudspeakers. 239 *Simultaneous Transmission Set: a set of media captures that can be 240 transmitted simultaneously from a Media Provider. 242 Spatial Relation: The arrangement in space of two objects, in 243 contrast to relation in time or other relationships. See also Left 244 and Right. 246 *Stream: RTP stream as in [RFC3550]. 248 Stream Characteristics: include media stream attributes commonly used 249 in non-CLUE SIP/SDP environments (such as: media codec, bit rate, 250 resolution, profile/level etc.) as well as CLUE specific attributes 251 (which could include for example and depending on the solution found: 252 the I-D or spatial location of a capture device a stream originates 253 from). 255 Telepresence: an environment that gives non co-located users or user 256 groups a feeling of (co-located) presence - the feeling that a Local 257 user is in the same room with other Local users and the Remote 258 parties. The inclusion of Remote parties is achieved through 259 multimedia communication including at least audio and video signals 260 of high fidelity. 262 *Video Capture: Media Capture for video. Denoted as VCn. 264 Video composite: A single image that is formed from combining visual 265 elements from separate sources. 267 4. Framework Features 269 Two key functions must be accomplished so that multiple media streams 270 can be handled in a telepresence conference. These are: 272 o How to choose which streams the provider should send to the 273 consumer 275 o What information needs to be added to the streams to allow a 276 rendering of the capture scene 278 The framework/model we present here can be understood as specifying 279 these two functions. 281 Media stream providers and consumers are central to the framework. 282 The provider's job is to advertise its capabilities (as described 283 here) to the consumer, whose job it is to configure the provider's 284 encoding capabilities as described below. Both providers and 285 consumers can each send and receive information, that is, we do not 286 have one party as the provider and one as the consumer exclusively, 287 but all parties have both sending and receiving parts to them. Most 288 devices function as both a media provider and as a media consumer. 290 For two devices to communicate bidirectionally, with media flowing in 291 both directions, both devices act as both a media provider and a 292 media consumer. The protocol exchange shown later in the "Choosing 293 Streams" section happens twice independently between the 2 294 bidirectional devices. 296 Both endpoints and MCUs, or more generally "middleboxes", can be 297 media providers and consumers. 299 Generally, the provider is capable of sending alternate captures of a 300 capture scene. These are described by the provider as capabilities 301 and chosen by the consumer. 303 5. Stream Information 305 This section describes the structure for communicating information 306 between providers and consumers. Figure illustrates how information 307 to be communicated is organized. Each construct illustrated in the 308 diagram is discussed in the sections below. 310 Diagram for Stream Content 312 +---------------+ 313 | | 314 | Capture Set | 315 | | 316 +-------+-------+ 317 _..-' | ``-._ 318 _.-' | ``-._ 319 _.-' | ``-._ 320 +----------------+ +----------------+ +----------------+ 321 | Media Capture | | Media Capture | | Media Capture | 322 | Audio or Video | | Audio or Video | | Audio or Video | 323 +----------------+ +----------------+ +----------------+ 324 .' `. `-..__ 325 .' `. ``-..__ 326 ,-----. ,---------. ``,----------. 327 ,' Encode`. ,' `. ,'Simultaneous`. 328 ( Group ) ( Attributes ) ( Transmission ) 329 `. ,' `. ,' `. Sets ,' 330 `-----' `---------' `----------' 332 5.1. Media capture -- Audio and Video 334 A media capture, as defined in definitions, is a fundamental concept 335 of the model. Media can be captured in different ways, for example 336 by various arrangements of cameras and microphones. The model uses 337 the terms "video capture" (VC) and "audio capture" (AC) to refer to 338 sources of media streams. To distinguish between multiple instances, 339 they are numbered for example VC1, VC2, and VC3 could refer to three 340 different video captures which can be used simultaneously. 342 Media captures are dynamic. They can come and go in a conference - 343 and their parameters can change. A provider can advertise a new list 344 of captures at any time. Both the media provider and media consumer 345 can send "their messages" (i.e., capture set advertisements, stream 346 configurations) any number of times during a call, and the other end 347 is always required to act on any new information received (e.g., 348 stopping streams it had previously configured that are no longer 349 valid). 351 A media capture can be a media source such as video from a specific 352 camera, or it can be more conceptual such as a composite image from 353 several cameras, or an automatic dynamically switched capture 354 choosing from several cameras depending on who is talking or other 355 factors. 357 A media capture is described by Attributes and associated with an 358 Encode Group, and Physical Simultaneity Set. 360 Audio and video captures are aggregated into Capture Sets as 361 described below. 363 5.2. Attributes 365 Audio and video capture attributes describe information about streams 366 and their relationships. [Edt: We do not mean to duplicate SDP, if 367 an SDP description can be used, great.] The attributes of media 368 captures refer to static aspects of those captures that can be used 369 by the consumer for selecting the captures offered by the provider. 371 The mechanism of Attributes make the framework extensible. Although 372 we are defining some attributes now based on the most common use 373 cases, new attributes can be added for new use cases as they arise. 374 In general, the way to extend the solution to handle new features is 375 by adding attributes and/or values. 377 We describe attributes by variables and their values. The current 378 attributes are listed below and then described. The variable is 379 shown in parentheses, and the values follow after the colon: 381 o (Purpose): main, presentation 383 o (Audio mixed): true, false 385 o (Audio Channel Format): mono, stereo, tbd 387 o (Area of Capture): A set of 'Ranges' describing the relevant area 388 being capture by a capture device 390 o (Point of Capture): A 'Point' describing the location of the 391 capture device or pseudo-device 393 o (Area scale): true, false indicating if area numbers are in 394 millimeters 396 o (Video composed): true, false 398 o (Auto-switched): true, false 400 5.2.1. Purpose 402 A variable with enumerated values describing the purpose or role of 403 the Media Capture. It could be applied to any media type. Possible 404 values: main, presentation, others TBD. 406 Main: 408 The audio or video capture is of one or more people participating in 409 a conference (or where they would be if they were there). It is of 410 part or all of the Capture Scene. 412 Presentation: 414 The stream provides a presentation, e. g., from a connected laptop or 415 other input device. 417 5.2.2. Audio mixed 419 A Boolean variable to indicate whether the AC is a mix of other ACs 420 or Streams. 422 5.2.3. Audio Channel Format 424 The "channel format" attribute of an Audio Capture indicates how the 425 meaning of the channels is determined. It is an enumerated variable 426 describing the type of audio channel or channels in the Audio 427 Capture. The possible values of the "channel format" attribute are: 429 o mono 431 o stereo 433 o TBD - other possible future values (to potentially include other 434 things like 3.0, 3.1, 5.1 surround sound and binaural) 436 All ACs in the same row of a Capture Set MUST have the same value of 437 the "channel format" attribute. 439 There can be multiple ACs of a particular type, or even different 440 types. These multiple ACs could each have an area of capture 441 attribute to indicate they represent different areas of the capture 442 scene. 444 If there are multiple audio streams, they might be correlated (that 445 is, someone talking might be heard in multiple captures from the same 446 room). Echo cancellation and stream synchronization in consumers 447 should take this into account. 449 Mono: 451 An AC with channel format="mono" has one audio channel. 453 Stereo: 455 An AC with channel format = "stereo" has exactly two audio channels, 456 left and right, as part of the same AC. [Edt: should we mention RFC 457 3551 here? The channel format may be related to how Audio Captures 458 are mapped to RTP streams. This stereo is not the same as the effect 459 produced from two mono ACs one from the left and one from the right. 460 ] 462 5.2.4. Area of capture 464 The area_of_capture attribute is used to describe the relevant area 465 of which a media capture is "capturing". By comparing the area of 466 capture for different media captures, a consumer can determine the 467 spatial relationships of the captures on the provider so that they 468 can be rendered correctly. The attribute consists of a set of 469 'Ranges', one range for each spatial dimension, where each range has 470 a Begin and End coordinate. It is not necessary to fill out all of 471 the dimensions if they are not relevant (i.e. if an endpoint's 472 captures only span a single dimension, only the 'x' coordinate can be 473 used). There is no need to pre-define a possible range for this 474 coordinate system; a device may choose what is most appropriate for 475 describing its captures. However, it is specified that as numbers 476 move from lower to higher, the location is going from: left to right 477 (in the case of the 'x' dimension), front to back (in the case of the 478 'y' dimension or low to high (in the case of the 'z' dimension). 480 5.2.5. Point of capture 482 The point_of_capture attribute can be used to describe the location 483 of a capture device or pseudo-device. If there are multiple captures 484 which share the same 'area_of_capture' value, then it is useful to 485 know the location from which they are capturing that area (e.g. a 486 device which has multiview). Point of capture is expressed as a 487 single {x, y, z} coordinate where, as with area_of_capture, only the 488 necessary dimensions need be expressed. 490 5.2.6. Area Scale Millimeters 492 An optional Boolean variable indicating if the numbers used for area 493 of capture and point of capture are in terms of millimeters. If this 494 attribute is true, then the x,y,z numbers represent millimeters. If 495 this attribute is false, then there is no physical scale. The 496 default value is false. 498 5.2.7. Video composed 500 An optional Boolean variable indicating if the VC is constructed by 501 composing multiple other video captures together. (This could 502 indicate for example a continuous presence view of multiple images in 503 a grid, or a large image with smaller picture-in-picture images in 504 it.) 506 Note: this attribute is not intended to differentiate between 507 different ways of composing images. For possible extension of the 508 framework, additional attributes could be defined to distinguish 509 between different ways of composing images, with different video 510 layout arrangements of composing multiple images into one. 512 5.2.8. Auto-switched 514 A Boolean variable that may be used or audio and/or video streams. 515 In this case the offered AC or VC varies depending on some rule; it 516 is auto-switched between possible VCs, or between possible ACs. The 517 most common example of this is sending the video capture associated 518 with the "loudest" speaker according to an audio detection algorithm. 520 5.3. Capture Set 522 A capture set describes the alternative media streams that the 523 provider offers to send to the consumer. As shown in the content 524 diagram above, the capture set is an aggregation of all audio and 525 video captures for a particular scene that a provider is willing to 526 send. 528 A provider describes its ability to send alternative media streams in 529 the capture set, which lists the media captures in rows, as shown 530 below. Each row of the capture set consists of either a single 531 capture or a group of captures. A group means the individual 532 captures in the group are spatially related with the specific 533 ordering of the captures described through the use of attributes. 535 Here is an example of a simple capture set with three video captures 536 and three audio channels: 538 (VC0, VC1, VC2) 540 (AC0, AC1, AC2) 542 The three VCs together in a row indicate those captures are spatially 543 related to each other. Similarly for the 3 ACs in the second row. 544 The ACs and VCs in the same capture set are spatially related to each 545 other. 547 Multiple Media Captures of the same media type are often spatially 548 related to each other. Typically multiple Video Captures should be 549 rendered next to each other in a particular order, or multiple audio 550 channels should be rendered to match different speakers in a 551 particular way. Also, media of different types are often associated 552 with each other, for example a group of Video Captures can be 553 associated with a group of Audio Captures meaning they should be 554 rendered together. 556 Media Captures of the same media type are associated with each other 557 by grouping them together in a single row of a Capture Set. Media 558 Captures of different media types are associated with each other by 559 putting them in different rows of the same Capture Set. 561 Since all captures have an area_of_capture associated with them, a 562 consumer can determine the spatial relationships of captures by 563 comparing the locations of their areas of capture with one another. 565 Association between audio and video can be made by finding audio and 566 video captures which share overlapping areas of capture. 568 The items (rows) in a capture set represent different alternatives 569 for representing the same Capture Scene. For example the following 570 are alternative ways of capturing the same Capture Scene - two 571 cameras each viewing half of a room, or one camera viewing the whole 572 room, or one stream that automatically captures the person in the 573 room who is currently speaking. Each row of the Capture Set contains 574 either a single media capture or one group of media captures. 576 The following example shows a capture set for an endpoint media 577 provider where: 579 o (VC0, VC1, VC2) - left camera capture, center camera capture, 580 right camera capture 582 o (VC3) - capture associated with loudest 584 o (VC4) - zoomed out view of all people in the room 586 o (AC0) - main audio 588 The first item in this capture set example is a group of video 589 captures with a spatial relationship to each other. These are VC0, 590 VC1, and VC2. VC3 and VC4 are additional alternatives of how to 591 capture the same room in different ways. The audio capture is 592 included in the same capture set to indicate AC0 is associated with 593 those video captures, meaning the audio should be rendered along with 594 the video in the same set. 596 The idea is to have sets of captures that represent the same 597 information ("information" in this context might be a set of people 598 and their associated audio / video streams, or might be a 599 presentation supplied by a laptop, perhaps with an accompanying audio 600 commentary). Spatial ordering of media captures is described through 601 the use of attributes. 603 A media consumer could choose one row of each media type (e.g., audio 604 and video) from a capture set. For example a three stream consumer 605 could choose the first video row plus the audio row, while a single 606 stream consumer could choose the second or third video row plus the 607 audio row. An MCU consumer might choose to receive multiple rows. 609 The groupsSimultaneous Transmission Set and Encoding Groups as 610 discussed in the next section apply to media captures listed in 611 capture sets. The groupsSimultaneous Transmission Sets and Encoding 612 Groups MUST allow all the Media Captures in a particular row of the 613 capture set to be used simultaneously. But media captures in 614 different rows of the capture set might not be able to be used 615 simultaneously. 617 6. Choosing Streams 619 This section describes the process of choosing which streams the 620 provider sends to the consumer. In order for appropriate streams to 621 be sent from providers to consumers, certain characteristics of the 622 multiple streams must be understood by both providers and consumers. 623 Two separate aspects of streams suffice to describe the necessary 624 information to be shared by providers and consumers. The first 625 aspect we call "physical simultaneity" and the other aspect we refer 626 to as "encoding group". These are described in the following 627 sections, after the message flow is discussed. 629 6.1. Message Flow 631 The following diagram shows the flow of messages between a media 632 provider and a media consumer. The provider sends information about 633 its capabilities (as specified in this section), then the consumer 634 chooses which streams it wants, which we refer to as "configure". 635 The consumer sends its own capability message to the provider which 636 may contain information about its own capabilities or restrictions, 637 in which case the provider might tailor its announcements to the 638 consumer. 640 Diagram for Message Flow 642 Media Consumer Media Provider 643 -------------- ------------ 644 | | 645 |----- Consumer Capability ---------->| 646 | | 647 | | 648 |<---- Capabilities (announce) -------| 649 | | 650 | | 651 |------ Configure (request) --------->| 652 | | 654 6.1.1. Provider Capabilities Announcement 656 The provider capabilities announce message includes: 658 o the list of captures and their attributes 660 o the list of capture sets 662 o the list of Simultaneous Transmission Sets 664 o the list of the encoding groups 666 6.1.2. Consumer Capability Message 668 In order for a maximally-capable provider to be able to advertise a 669 manageable number of video captures to a consumer, there is a 670 potential use for the consumer being able, at the start of CLUE to be 671 able to inform the provider of its capabilities. One example here 672 would be the video capture attribute set - a consumer could tell the 673 provider the complete set of video capture attributes it is able to 674 understand and so the provider would be able to reduce the capture 675 set it advertises to be tailored to the consumer. 677 TBD - the content of this message needs to be better defined. The 678 authors believe there is a need for this message, but have not worked 679 out the details yet. 681 6.1.3. Consumer Configure Request 683 After receiving a set of video capture information from a provider 684 and making its choice of what media streams to receive based on the 685 consumer's own capabilities and any provider-side simultaneity 686 restrictions, the consumer needs to essentially configure the 687 provider to transmit the chosen set. 689 The expectation is that this message will enumerate each of the 690 encoding groups and potential encoders within those groups that the 691 consumer wishes to be active (this may well be a subset of the 692 complete set available). For each such encoder within an encoding 693 group, the consumer would specify the video capture (i.e., VC as 694 described above) along with the specifics of the video encoding 695 required, i.e. width, height, frame rate and bit rate. At this 696 stage, the consumer would also provide RTP demultiplexing information 697 as required to distinguish each stream from the others being 698 configured by the same mechanism. 700 6.2. Physical Simultaneity 702 An endpoint or MCU can send multiple captures simultaneously. 703 However, there may be constraints that limit which captures can be 704 sent simultaneously with other captures. 706 Physical or device simultaneity refers to fact that a device may not 707 be able to be used in different ways at the same time. This shapes 708 the way that offers are made from the provider. The offers are made 709 so that the consumer will choose one of several possible usages of 710 the device. This type of constraint is expressed in Simultaneous 711 Transmission Sets. This is easier to show in an example. 713 Consider the example of a room system where there are 3 cameras each 714 of which can send a separate capture covering 2 persons each- VC0, 715 VC1, VC2. The middle camera can also zoom out and show all 6 716 persons, VC3. But the middle camera cannot be used in both modes at 717 the same time - it has to either show the space where 2 participants 718 sit or the whole 6 seats. We refer to this as a physical device 719 simultaneity constraint. 721 The following illustration shows 3 cameras with 4 video streams. The 722 middle camera can be used as main video zoomed in on 2 people or it 723 could be used in zoomed out mode and capture the whole endpoint. The 724 idea here is that the middle camera cannot be used for both zoomed in 725 and zoomed out captures simultaneously. This is a constraint imposed 726 by the physical limitations of the devices. 728 Diagram for Simultaneity 730 `-. +--------+ VC2 731 .-'_Camera 3|----------> 732 .-' +--------+ 733 VC3 734 --------> 735 `-. +--------+ / 736 .-'|Camera 2|< 737 .-' +--------+ \ VC1 738 --------> 740 `-. +--------+ VC0 741 .-'|Camera 1|----------> 742 .-' +--------+ 744 VC0- video zoomed in on 2 people VC2- video zoomed in on 2 people 745 VC1- video zoomed in on 2 people VC3- video zoomed out on 6 people 747 Simultaneous transmission sets can be expressed as sets of the VCs 748 that could physically be transmitted at the same time, though it may 749 not make sense to do so. 751 In this example the two simultaneous sets are: 753 {VC0, VC1, VC2} 755 {VC0, VC3, VC2} 757 In this example VC0, VC1 and VC2 can be sent OR VC0, VC3 and VC2. 758 Only one set can be transmitted at a time. These are physical 759 capabilities describing what can physically be sent at the same time, 760 not what might make sense to send. For example, in the second set 761 both VC0 and VC2 are redundant if VC3 is included. 763 In describing its capabilities, the provider must take physical 764 simultaneity into account and send a list of its Simultaneous 765 Transmission Sets to the consumer, along with the Capture Sets and 766 Encoding Groups. 768 6.3. Encoding Groups 770 The second aspect of multiple streams that must be understood by 771 providers and consumers in order to create the best experience 772 possible, i. e., for the "right" or "best" streams to be sent, is the 773 encoding characteristics of the possible audio and video streams 774 which can be sent. Just as in the way that a constraint is imposed 775 on the multiple streams due to the physical limitations, there are 776 also constraints due to encoding limitations. These are described by 777 four variables that make up an Encoding Group, as shown in the 778 following table: 780 Table: Encoding Group 782 +----------------+--------------------------------------------------+ 783 | Name | Description | 784 +----------------+--------------------------------------------------+ 785 | maxBandwidth | Maximum number of bits per second relating to | 786 | | all encodes combined | 787 | maxVideoMbps | Maximum number of macroblocks per second | 788 | | relating to a all video encodes combined ((width | 789 | | + 15) / 16) * ((height + 15) / 16) * | 790 | | framesPerSecond | 791 | videoEncodes[] | Set of potential video encodes can be generated | 792 | audioEncodes[] | Set of potential encodes that can be generated | 793 +----------------+--------------------------------------------------+ 795 An encoding group is the basic concept for describing encoding 796 capability. As shown in the Table, it has an overall maxMbps and 797 bandwidth limits, as well as being comprised of sets of individual 798 encodes, which will be described in more detail below. 800 Each media stream provider includes one or more encoding groups. 801 There may be multiple encoding groups per endpoint. For example, 802 each video capture device might have an associated encoding group 803 that describes the video streams that can result from that capture. 805 A remote receiver (i. e., stream consumer)configures some or all of 806 the specific encodings within one or more groups in order to provide 807 it with media streams to decode. 809 6.3.1. Encoding Group Structure 811 This section shows more detail on the media stream provider's 812 encoding group structure. The encoding group includes several 813 individual encodes, each has different encoding values. For example 814 one may be high definition video 1080p60, and another 720p30, with a 815 third being CIF. While a typical 3 codec/display system would have 816 one encoding group per "box", there are many possibilities for the 817 number of encoding groups a provider may be able offer and for what 818 encoding values there are in each encoding group. 820 Diagram for Encoding Group Structure 822 ,-------------------------------------------------. 823 | Media Provider | 824 | | 825 | ,--------------------------------------. | 826 | | ,--------------------------------------. | 827 | | | ,--------------------------------------. | 828 | | | | Encoding Group | | 829 | | | | ,-----------. | | 830 | | | | | | ,---------. | | 831 | | | | | | | | ,---------.| | 832 | | | | | Encode1 | | Encode2 | | Encode3 || | 833 | `.| | | | | | `---------'| | 834 | `.| `-----------' `---------' | | 835 | `--------------------------------------' | 836 `-------------------------------------------------' 838 As shown in the diagram, each encoding group has multiple potential 839 individual encodes within it. Not all encodes are equally capable, 840 the stream consumer chooses the encodes it wants by configuring the 841 provider to send it what it wants to receive. 843 Some encoding endpoints are fixed, others are flexible, e. g., a 844 single box with multiple DSPs where the resources are shared. 846 6.3.2. Individual Encodes 848 An encoding group is associated with a media capture through the 849 individual encodes, that is, an audio or video capture is encoded in 850 one or more individual encodes, as described by the videoEncodes[] 851 and audioEncodes[]variables. 853 The following table shows the variables for a Video Encode. (There 854 is a similar table for audio.) 855 Table: Individual Video Encode 857 +--------------+----------------------------------------------------+ 858 | Name | Description | 859 +--------------+----------------------------------------------------+ 860 | maxBandwidth | Maximum number of bits per second relating to a | 861 | | single video encoding | 862 | maxMbps | Maximum number of macroblocks per second relating | 863 | | to a single video encoding: ((width + 15) / 16) * | 864 | | ((height + 15) / 16) * framesPerSecond | 865 | maxWidth | Video resolution's maximum supported width, | 866 | | expressed in pixels | 867 | maxHeight | Video resolution's maximum supported height, | 868 | | expressed in pixels | 869 | maxFrameRate | Maximum supported frame rate | 870 +--------------+----------------------------------------------------+ 872 A remote receiver configures (i. e., instantiates) some or all of the 873 specific encodes such that: 875 o The configuration of each active ENC does not exceed that 876 individual encode's maxWidth, maxHeight, maxFrameRate. 878 o The total bandwidth of the configured ENC comprises one or more potential encodings 890 ENC. For example, 892 EG0: maxMbps=489600, maxBandwidth=6000000 893 VIDEO_ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60, 894 maxMbps=244800, maxBandwidth=4000000 895 VIDEO_ENC1: maxWidth=1920, maxHeight=1088, maxFrameRate=60, 896 maxMbps=244800, maxBandwidth=4000000 897 AUDIO_ENC0: maxBandwidth=96000 898 AUDIO_ENC1: maxBandwidth=96000 899 AUDIO_ENC2: maxBandwidth=96000 901 Here, the encoding group is EG0. It can transmit up to two 1080p30 902 encodings (Mbps for 1080p = 244800), but it is capable of 903 transmitting a maxFrameRate of 60 frames per second (fps). To 904 achieve the maximum resolution (1920 x 1088) the frame rate is 905 limited to 30 fps. However 60 fps can be achieved at a lower 906 resolution if required by the consumer. Although the encoding group 907 is capable of transmitting up to 6Mbit/s, no individual video 908 encoding can exceed 4Mbit/s. 910 This encoding group also allows up to 3 audio encodings, 911 AUDIO_ENC<0-2>. It is not required that audio and video encodings 912 reside within the same encoding group, but if so then the group's 913 overall maxBandwidth value is a limit on the sum of all audio and 914 video encodings configured by the consumer. A system that does not 915 wish or need to combine bandwidth limitations in this way should 916 instead use separate encoding groups for audio and video in order for 917 the bandwidth limitations on audio and video to not interact. 919 Audio and video can be expressed in separate encode groups, as in 920 this illustration. 922 VIDEO_EG0: maxMbps=489600, maxBandwidth=6000000 923 VIDEO_ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60, 924 maxMbps=244800, maxBandwidth=4000000 925 VIDEO_ENC1: maxWidth=1920, maxHeight=1088, maxFrameRate=60, 926 maxMbps=244800, maxBandwidth=4000000 927 AUDIO_EG0: maxBandwidth=500000 928 AUDIO_ENC0: maxBandwidth=96000 929 AUDIO_ENC1: maxBandwidth=96000 930 AUDIO_ENC2: maxBandwidth=96000 932 6.3.4. Examples of Encoding Groups 934 This section illustrates further examples of encoding groups. In the 935 first example, the capability parameters are the same across ENCs. 936 In the second example, they vary. 938 An endpoint that has 3 similar video capture devices would advertise 939 3 encoding groups that can each transmit up to 2 1080p30 encodings, 940 as follows: 942 EG0: maxMbps = 489600, maxBandwidth=6000000 943 ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60, 944 maxMbps=244800, maxBandwidth=4000000 945 ENC1: maxWidth=1920, maxHeight=1088, maxFrameRate=60, 946 maxMbps=244800, maxBandwidth=4000000 947 EG1: maxMbps = 489600, maxBandwidth=6000000 948 ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60, 949 maxMbps=244800, maxBandwidth=4000000 950 ENC1: maxWidth=1920, maxHeight=1088, maxFrameRate=60, 951 maxMbps=244800, maxBandwidth=4000000 952 EG2: maxMbps = 489600, maxBandwidth=6000000 953 ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60, 954 maxMbps=244800, maxBandwidth=4000000 955 ENC1: maxWidth=1920, maxHeight=1088, maxFrameRate=60, 956 maxMbps=244800, maxBandwidth=4000000 958 A remote consumer configures some or all of the specific encodings 959 such that: 961 o The configuration of each active ENC parameter values does not 962 cause that encoding's maxWidth, maxHeight, maxFrameRate to be 963 exceeded 965 o The total bandwidth of the configured ENC encodings does not 966 exceed the maxBandwidth of the encoding group 968 o The sum of the "macroblocks per second" values of each configured 969 encoding does not exceed the maxMbps of the encoding group 971 There is no requirement for all encodings within an encoding group to 972 be activated when configured by the consumer. 974 Depending on the provider's encoding methods, the consumer may be 975 able to request fixed encode values or choose encode values in the 976 range less than the maximum offered. We will discuss consumer 977 behavior in more detail in a section below. 979 6.3.4.1. Sample video encoding group specification #2 981 This example specification expresses a system whose encoding groups 982 can each transmit up to 3 encodings, but with each potential encoding 983 having a progressively lower specification. In this example, 1080p60 984 transmission is possible (as ENC0 has a maxMbps value compatible with 985 that) as long as it is the only active encoding (as maxMbps for the 986 entire encoding group is also 489600). Significantly, as up to 3 987 encodings are available per group, some sets of captures which 988 weren't able to be transmitted simultaneously in example #1 above now 989 become possible, for instance VC1, VC3 and VC6 together. In common 990 with example #1, all encoding groups have an identical specification. 992 EG0: maxMbps = 489600, maxBandwidth=6000000 993 ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60, 994 maxMbps=489600, maxBandwidth=4000000 995 ENC1: maxWidth=1280, maxHeight=720, maxFrameRate=30, 996 maxMbps=108000, maxBandwidth=4000000 997 ENC2: maxWidth=960, maxHeight=544, maxFrameRate=30, 998 maxMbps=61200, maxBandwidth=4000000 999 EG1: maxMbps = 489600, maxBandwidth=6000000 1000 ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60, 1001 maxMbps=489600, maxBandwidth=4000000 1002 ENC1: maxWidth=1280, maxHeight=720, maxFrameRate=30, 1003 maxMbps=108000, maxBandwidth=4000000 1004 ENC2: maxWidth=960, maxHeight=544, maxFrameRate=30, 1005 maxMbps=61200, maxBandwidth=4000000 1006 EG2: maxMbps = 489600, maxBandwidth=6000000 1007 ENC0: maxWidth=1920, maxHeight=1088, maxFrameRate=60, 1008 maxMbps=489600, maxBandwidth=4000000 1009 ENC1: maxWidth=1280, maxHeight=720, maxFrameRate=30, 1010 maxMbps=108000, maxBandwidth=4000000 1011 ENC2: maxWidth=960, maxHeight=544, maxFrameRate=30, 1012 maxMbps=61200, maxBandwidth=4000000 1014 7. Using the Framework 1016 This section shows in more detail how to use the framework to 1017 represent a typical case for telepresence rooms. First an endpoint 1018 is illustrated, then an MCU case is shown. 1020 Consider an endpoint with the following characteristics: 1022 o 3 cameras, 3 displays, a 6 person table 1024 o Each video device can provide one capture for each 1/3 section of 1025 the table 1027 o A single capture representing the active speaker can be provided 1029 o A single capture representing the active speaker with the other 2 1030 captures shown picture in picture within the stream can be 1031 provided 1033 o A capture showing a zoomed out view of all 6 seats in the room can 1034 be provided 1036 The audio and video captures for this endpoint can be described as 1037 follows. The Encode Group specifications can be found above in 1038 Section 6.3.4.1, Sample video encoding group specification #2. 1040 Video Captures: 1042 o VC0- (the left camera stream), encoding group:EG0, attributes: 1043 purpose=main;auto-switched:no; area_of_capture={xBegin=0, xEnd=33} 1045 o VC1- (the center camera stream), encoding group:EG1, attributes: 1046 purpose=main; auto-switched:no; area_of_capture={xBegin=33, 1047 xEnd=66} 1049 o VC2- (the right camera stream), encoding group:EG2, attributes: 1050 purpose=main;auto-switched:no; area_of_capture={xBegin=66, 1051 xEnd=99} 1053 o VC3- (the loudest panel stream), encoding group:EG1, attributes: 1054 purpose=main;auto-switched:yes; area_of_capture={xBegin=0, 1055 xEnd=99} 1057 o VC4- (the loudest panel stream with PiPs), encoding group:EG1, 1058 attributes: purpose=main; composed=true; auto-switched:yes; 1059 area_of_capture={xBegin=0, xEnd=99} 1061 o VC5- (the zoomed out view of all people in the room), encoding 1062 group:EG1, attributes: purpose=main;auto-switched:no; 1063 area_of_capture={xBegin=0, xEnd=99} 1065 o VC6- (presentation stream), encoding group:EG1, attributes: 1066 purpose=presentation;auto-switched:no; area_of_capture={xBegin=0, 1067 xEnd=99} 1069 Summary of video captures - 3 codecs, center one is used for center 1070 camera stream, presentation stream, auto-switched, and zoomed views. 1072 Note the text in parentheses (e.g. "the left camera stream") is not 1073 explicitly part of the model, it is just explanatory text for this 1074 example, and is not included in the model with the media captures and 1075 attributes. 1077 [edt. It is arbitrary that for this example the alternative views 1078 are on EG1 - they could have been spread out- it was not a necessary 1079 choice.] 1081 Audio Captures: 1083 o AC0 (left), attributes: purpose=main;channel format=mono; 1084 area_of_capture={xBegin=0, xEnd=33} 1086 o AC1 (right), attributes: purpose=main;channel format=mono; 1087 area_of_capture={xBegin=66, xEnd=99} 1089 o AC2 (center) attributes: purpose=main;channel format=mono; 1090 area_of_capture={xBegin=33, xEnd=66} 1092 o AC3 being a simple pre-mixed audio stream from the room (mono), 1093 attributes: purpose=main;channel format=mono; mixed=true; 1094 area_of_capture={xBegin=0, xEnd=99} 1096 o AC4 audio stream associated with the presentation video (mono) 1097 attributes: purpose=presentation;channel format=mono; 1098 area_of_capture={xBegin=0, xEnd=99} 1100 The physical simultaneity information is: 1102 {VC0, VC1, VC2, VC3, VC4, VC6} 1104 {VC0, VC2, VC5, VC6} 1106 It is possible to select any or all of the rows in a capture set. 1107 This is strictly what is possible from the devices. However, using 1108 every member in the set simultaneously may not make sense- for 1109 example VC3(loudest) and VC4 (loudest with PIP). (In addition, there 1110 are encoding constraints that make choosing all of the VCs in a set 1111 impossible. VC1, VC3, VC4, VC5, VC6 all use EG1 and EG1 has only 3 1112 ENCs. This constraint shows up in the Capture list and encoding 1113 groups, not in the simultaneous transmission sets.) 1115 In this example there are no restrictions on which audio captures can 1116 be sent simultaneously. 1118 The following table represents the capture sets for this provider. 1119 Recall that a capture set is composed of alternative captures 1120 covering the same scene. Capture Set #1 is for the main people 1121 captures, and Capture Set #2 is for presentation. 1123 +----------------+ 1124 | Capture Set #1 | 1125 +----------------+ 1126 | VC0, VC1, VC2 | 1127 | VC3 | 1128 | VC4 | 1129 | VC5 | 1130 | AC0, AC1, AC2 | 1131 | AC3 | 1132 +----------------+ 1134 +----------------+ 1135 | Capture Set #2 | 1136 +----------------+ 1137 | VC6 | 1138 | AC4 | 1139 +----------------+ 1141 Different capture sets are unique to each other, non-overlapping. A 1142 consumer chooses a capture row from each capture set. In this case 1143 the three captures VC0, VC1, and VC2 are one way of representing the 1144 video from the endpoint. These three captures should appear adjacent 1145 next to each other. Alternatively, another way of representing the 1146 Capture Scene is with the capture VC3, which automatically shows the 1147 person who is talking. Similarly for the VC4 and VC5 alternatives. 1149 As in the video case, the different rows of audio in Capture Set #1 1150 represent the "same thing", in that one way to receive the audio is 1151 with the 3 linear position audio captures (AC0, AC1, AC2), and 1152 another way is with the single channel monaural format AC3. The 1153 Media Consumer would choose the one audio capture row it is capable 1154 of receiving. 1156 The spatial ordering is understood by the media capture attributes 1157 area and point of capture. 1159 The consumer finds a "row" in each capture set #x section of the 1160 table that it wants. It configures the streams according to the 1161 encoding group for the row. 1163 A Media Consumer would likely want to choose a row to receive based 1164 in part on how many streams it can simultaneously receive. A 1165 consumer that can receive three people streams would probably prefer 1166 to receive the first row of Capture Set #1 (VC0, VC1, VC2) and not 1167 receive the other rows. A consumer that can receive only one people 1168 stream would probably choose one of the other rows. 1170 If the consumer can receive a presentation stream too, it would also 1171 choose to receive the only row from Capture Set #2 (VC6). 1173 7.1. The MCU Case 1175 This section shows how an MCU might express its Capture Sets, 1176 intending to offer different choices for consumers that can handle 1177 different numbers of streams. A single audio capture stream is 1178 provided for all single and multi-screen configurations that can be 1179 associated (e.g. lip-synced) with any combination of video captures 1180 at the consumer. 1182 +--------------------+---------------------------------------------+ 1183 | Capture Set #1 | note | 1184 +--------------------+---------------------------------------------+ 1185 | VC0 | video capture for single screen consumer | 1186 | VC1, VC2 | video capture for 2 screen consumer | 1187 | VC3, VC4, VC5 | video capture for 3 screen consumer | 1188 | VC6, VC7, VC8, VC9 | video capture for 4 screen consumer | 1189 | AC0 | audio capture representing all participants | 1190 +--------------------+---------------------------------------------+ 1192 If / when a presentation stream becomes active within the conference, 1193 the MCU might re-advertise the available media as: 1195 +----------------+--------------------------------------+ 1196 | Capture Set #2 | note | 1197 +----------------+--------------------------------------+ 1198 | VC10 | video capture for presentation | 1199 | AC1 | presentation audio to accompany VC10 | 1200 +----------------+--------------------------------------+ 1202 7.2. Media Consumer Behavior 1204 [Edt. Should this be moved to appendix?] 1206 The receive side of a call needs to balance its requirements, based 1207 on number of screens and speakers, its decoding capabilities and 1208 available bandwidth, and the provider's capabilities in order to 1209 optimally configure the provider's streams. Typically it would want 1210 to receive and decode media from each capture set advertised by the 1211 provider. 1213 A sane, basic, algorithm might be for the consumer to go through each 1214 capture set in turn and find the collection of video captures that 1215 best matches the number of screens it has (this might include 1216 consideration of screens dedicated to presentation video display 1217 rather than "people" video) and then decide between alternative rows 1218 in the video capture sets based either on hard-coded preferences or 1219 user choice. Once this choice has been made, the consumer would then 1220 decide how to configure the provider's encode groups in order to make 1221 best use of the available network bandwidth and its own decoding 1222 capabilities. 1224 7.2.1. One screen consumer 1226 VC3, VC4 and VC5 are all on different rows by themselves, not in a 1227 group, so the receiving device should choose between one of those. 1228 The choice would come down to whether to see the greatest number of 1229 participants simultaneously at roughly equal precedence (VC5), a 1230 switched view of just the loudest region (VC3) or a switched view 1231 with PiPs (VC4). An endpoint device with a small amount of knowledge 1232 of these differences could offer a dynamic choice of these options, 1233 in-call, to the user. 1235 7.2.2. Two screen consumer configuring the example 1237 Mixing systems with an even number of screens, "2n", and those with 1238 "2n+1" cameras (and vice versa) is always likely to be the 1239 problematic case. In this instance, the behavior is likely to be 1240 determined by whether a "2 screen" system is really a "2 decoder" 1241 system, i.e., whether only one received stream can be displayed per 1242 screen or whether more than 2 streams can be received and spread 1243 across the available screen area. To enumerate 3 possible behaviors 1244 here for the 2 screen system when it learns that the far end is 1245 "ideally" expressed via 3 capture streams: 1247 v 1249 1. Fall back to receiving just a single stream (VC3, VC4 or VC5 as 1250 per the 1 screen consumer case above) and either leave one screen 1251 blank or use it for presentation if / when a presentation becomes 1252 active 1254 2. Receive 3 streams (VC0, VC1 and VC2) and display across 2 screens 1255 (either with each capture being scaled to 2/3 of a screen and the 1256 centre capture being split across 2 screens) or, as would be 1257 necessary if there were large bezels on the screens, with each 1258 stream being scaled to 1/2 the screen width and height and there 1259 being a 4th "blank" panel. This 4th panel could potentially be 1260 used for any presentation that became active during the call. 1262 3. Receive 3 streams, decode all 3, and use control information 1263 indicating which was the most active to switch between showing 1264 the left and centre streams (one per screen) and the centre and 1265 right streams. 1267 For an endpoint capable of all 3 methods of working described above, 1268 again it might be appropriate to offer the user the choice of display 1269 mode. 1271 7.2.3. Three screen consumer configuring the example 1273 This is the most straightforward case - the consumer would look to 1274 identify a set of streams to receive that best matched its available 1275 screens and so the VC0 plus VC1 plus VC2 should match optimally. The 1276 spatial ordering would give sufficient information for the correct 1277 video capture to be shown on the correct screen, and the consumer 1278 would either need to divide a single encode group's capability by 3 1279 to determine what resolution and frame rate to configure the provider 1280 with or to configure the individual video captures' encode groups 1281 with what makes most sense (taking into account the receive side 1282 decode capabilities, overall call bandwidth, the resolution of the 1283 screens plus any user preferences such as motion vs sharpness). 1285 8. Acknowledgements 1287 Mark Gorzyinski contributed much to the approach. We want to thank 1288 Stephen Botzko for helpful discussions on audio. 1290 9. IANA Considerations 1292 TBD 1294 10. Security Considerations 1296 TBD 1298 11. Informative References 1300 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1301 Requirement Levels", BCP 14, RFC 2119, March 1997. 1303 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 1304 A., Peterson, J., Sparks, R., Handley, M., and E. 1305 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 1306 June 2002. 1308 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 1309 Jacobson, "RTP: A Transport Protocol for Real-Time 1310 Applications", STD 64, RFC 3550, July 2003. 1312 [RFC4353] Rosenberg, J., "A Framework for Conferencing with the 1313 Session Initiation Protocol (SIP)", RFC 4353, 1314 February 2006. 1316 [RFC5117] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 5117, 1317 January 2008. 1319 Appendix A. Open Issues 1321 A.1. Video layout arrangements and centralized composition 1323 In the context of a conference with a central MCU, there has been 1324 discussion about a consumer requesting the provider to provide a 1325 certain type of layout arrangement or perform a certain composition 1326 algorithm, such as combining some number of most recent talkers, or 1327 producing a video layout using a 2x2 grid or 1 large cell with 5 1328 smaller cells around it. The current framework does not address 1329 this. It isn't clear if this topic should be included in this 1330 framework, or maybe a different part of CLUE, or maybe outside of 1331 CLUE altogether. 1333 A.2. Source is selectable 1335 A Boolean variable. True indicates the media consumer can request a 1336 particular media source be mapped to a media capture. Default is 1337 false. 1339 TBD - how does the consumer make the request for a particular source? 1340 How does the consumer know what is available? Need to explain better 1341 how multiple media captures are different from a single media capture 1342 with choices for the source, and when each concept should be used. 1344 A.3. Media Source Selection 1346 The use cases include a case where the person at a receiving endpoint 1347 can request to receive media from a particular other endpoint, for 1348 example in a multipoint call to request to receive the video from a 1349 certain section of a certain room, whether or not people there are 1350 talking. 1352 TBD - this framework should address this case. Maybe need a roster 1353 list of rooms or people in the conference, with a mechanism to select 1354 from the roster and associate it with media captures. This is 1355 different from selecting a particular media capture from a capture 1356 set. The mechanism to do this will probably need to be different 1357 than selecting media captures based on capture sets and attributes. 1359 A.4. Endpoint requesting many streams from MCU 1361 TBD - how to do VC selection for a system where the endpoint media 1362 consumers want to receive lots of streams and do their own 1363 composition, rather than MCU doing transcoding and composing. 1364 Example is 3 screen consumer that wants 3 large loudest speaker 1365 streams, and a bunch of small ones to render as PiP. How the small 1366 ones are chosen, which could potentially be chosen by either the 1367 endpoint or MCU. There are other more complicated examples also. Is 1368 the current framework adequate to support this? 1370 A.5. VAD (voice activity detection) tagging of audio streams 1372 TBD - do we want to have VAD be mandatory? All audio streams 1373 originating from a media provider must be tagged with VAD 1374 information. This tagging would include an overall energy value for 1375 the stream plus information on which sections of the capture scene 1376 are "active". 1378 Each audio stream which forms a constituent of a row within a capture 1379 set should include this tagging, and the energy value within it 1380 calculated using a fixed, consistent algorithm. 1382 When a system determines the most active area of a capture scene 1383 (either "loudest", or determined by other means such as a button 1384 press) it should convey that information to the corresponding media 1385 stream consumer via any audio streams being sent within that capture 1386 set. Specifically, there should be a list of active linear positions 1387 and their VAD characteristics within the audio stream in addition to 1388 the overall VAD information for the capture set. This is to ensure 1389 all media stream consumers receive the same, consistent, audio energy 1390 information whichever audio capture or captures they choose to 1391 receive for a capture set. Additionally, linear position information 1392 can be mapped to video captures by a media stream consumer in order 1393 that it can perform "panel switching" if required. 1395 A.6. Private Information 1397 Authors' Addresses 1399 Allyn Romanow 1400 Cisco Systems 1401 San Jose, CA 95134 1402 USA 1404 Email: allyn@cisco.com 1405 Mark Duckworth 1406 Polycom 1407 Andover, MA 01810 1408 US 1410 Email: mark.duckworth@polycom.com 1412 Andrew Pepperell 1413 Cisco Systems 1414 Langley, England 1415 UK 1417 Email: apeppere@cisco.com 1419 Brian Baldino 1420 Cisco Systems 1421 San Jose, CA 95134 1422 US 1424 Email: bbaldino@cisco.com