RTC Accessibility User Requirements

1.1 Real-time communication and accessibility

RTC has the potential to allow improved accessibility features that will support a broad range of user needs for people with a wide range of disabilities. These needs can be met through improved audio and video quality, audio routing, captioning, improved live transcription, transfer of alternate formats such as sign-language, text-messaging / chat, real time user support and status polling.

Accessible RTC is enabled by a combination of technologies and specifications such as those from the Media Working Group, Web and Networks IG, Second Screen, and Web Audio Working group as well as AGWG and ARIA. APA hopes this document will inform how these groups meet various responsibilities for enabling accessible RTC, as well updating related use cases in various groups. For examples, view the current work on WebRTC Next Version Use Cases First Public Working Draft. [webrtc-use-cases]

1.2 User needs definition

This document outlines various accessibility related user needs for Accessible RTC. These user needs should drive accessibility requirements for Accessible RTC and its related architecture.

User needs are presented here with their related requirements; some in a range of scenarios (which can be thought of as similar to user stories). User needs and requirements are being actively reviewing by RQTF/APA.

2.1 Incoming calls and caller ID

• User Need 1: A screen-reader user or user with a cognitive impairment needs to know a call is incoming and needs to recognise the ID of the caller.
• REQ 1a: Provide indicatation of incoming calls in an unobtrusive way via a symbol set or other browser notification.
• REQ 1b: Alert assistive technologies via relevant APIs.

2.2 Routing and communication channel control

• User Need 2: A blind user of both screen reader and braille output devices may need to manage audio and text output differently e.g. once they have accepted the call a user may wish to route notifications to a separate braille device while continuing the call on bluetooth headphones.
• REQ 2a: Provide or support a range of browser level audio output and routing options.
• REQ 2b: Allow controlled routing of alerts and other browser output to a braille device or other hardware.

• User Need 3: A deaf user needs to move parts of a live teleconference session (as separate streams) to one or more devices for greater control.
• REQ 3a: Allow the separate routing of video streams such as a sign language interpreter to a separate high resolution display.

• User Need 4: Users with cognitive disabilities or blind users may have relative volume levels set as preferences that relate to importance, urgency or meaning.
• REQ 4a: Allow the panning or setting of relative levels of different audio output.
• REQ 4b: Support multichannel audio in the browser.

2.3 Dynamic audio description values in live conferencing

• User Need 5: A user may struggle to hear audio description in a live teleconferencing situation.
• REQ 5a: Ensure Audio Description (AD) recommended sound values are dynamic.

2.4 Quality synchronisation and playback

• User Need 6: Any deaf or hard of hearing user watching captioning or audio description needs to be confident it is synchronised and accurate.
• REQ 6a: Ensure that any outages or loss to captioning or audio description will be repaired while preserving context and meaning.
• REQ 6b: Ensure that the integrity of related alternate supporting tracks or streams such as transcriptions, are in sync with any repairs.

2.5 Simultaneous voice, text & signing

• User Need 7: A deaf user needs to simultaneously talk on a call, send and receive instant messages via a text interface and watch sign language using a video stream.
• REQ 7a: Ensure support for multiple simultaneous streams.

2.6 Emergency calls: Support for Real-time text (RTT)

• User Need 8: In an emergency situation a deaf, speech impaired, hard of hearing or deaf blind user needs to make an emergency call, instantly send and receive related text messages and/or sign via a video stream.
• REQ 8a: Provide or ensure support for RTT in WebRTC.

2.7 Video relay services (VRS) and remote interpretation (VRI)

• User Need 9: A deaf, speech impaired, or hard of hearing user, needs to communicate on a call using a remote video interpretation service to access sign language and interpreter services.
• REQ 9a: Provide or ensure support for video relay and remote interpretation services. This user need may relate to interoperability with third-party services; IETF has looked at standardizing a way to use Session Initiation Protocol (SIP) with VRS services. [ietf-relay] VRS calls may be made between ASL (American Sign Language) users and hearing persons speaking either English or Spanish.

2.8 Distinguishing sent and received text with RTT

• User Need 10: A deaf or deaf blind user needs to tell the difference between incoming text and outgoing text.
• REQ 10a: Ensure when used with RTT functionality, WebRTC handles the routing of this information to a format or output of the users choosing.

2.9 Call participants and status

• User Need 11: In a teleconference a blind screen-reader user needs to know what participants are on the call, as well as their status.
• REQ 11a: Ensure participant details such as name and status; whether the person is muted or talking is accessible to users of Assistive Technologies.

2.10 Live transcription and captioning support

• User Need 12: A deaf user or user with a cognitive disability needs to access a channel containing live transcriptions or captioning during a conference call or broadcast.
• REQ 12a: Honor user preferences relating to live transcription and captioning e.g. provide support for signing or a related symbol set.

2.11 Assistance for users with cognitive disabilities

• User Need 13: Users with cognitive disabilities may need assistance when using audio or video communication.
• REQ 13a: Ensure a WebRTC video call can host a technical or user support channel.
• REQ 13b: Provide support that is customised to the needs of the user.

2.12 Personalized symbol sets for users with cognitive disabilities

• User Need 14: Users with cognitive disabilities may need to use symbol sets for identifying functions available in a WebRTC enabled client for voice, file or data transfer.

• REQ 14a: Provide personalization support for symbols set replacements of existing user interface rendering of current functions or controls.

2.13 Internet relay chat (IRC) style interfaces required by blind users

• User Need 15: To translate text to speech interactions into comprehensible speech; a blind screen reader user depending on TTS to interact with their computers and smart devices needs a traditional Internet Relay Chat (IRC) style interface.
• REQ 15a: Preserve IRC as a configuration option in agents that implement WebRTC as opposed to having only the Real-time text (RTT) type interface. While (RTT) is very imporant it is favoured by users who are deaf or hearing impaired. For screen reader users, TTS cannot reasonably translate text into comprehensible speech unless the characters to be pronounced are transmitted in very close timing to one another. Typical gaps will result in stuttering and highly unintelligible output from the TTS engine.

  Braille users and RTT

  Some braille users will also prefer the RTT model. However, braille users desiring text displayed with standard contracted braille might better be served in the manner users relying on text to speech (TTS) engines are served, by buffering the data to be transmitted until an end of line character is reached.

2.14 Deaf users: Video resolution and frame rates

• User Need 15: A deaf user watching a signed broadcast needs a high-quality frame rate to maintain legibility and clarity in order to understand what is being signed.

  NOTE: EN 301 549 Section 6, recommends WebRTC applications should support a frame rate of at least 20 frames per second (FPS). More details can be found at Accessible Procurement standard for ICT products and services EN 301 549 (PDF)

3.1 Bandwidth for audio

Scenario: A hard of hearing user needs better stereo sound to have a quality experience in work calls or meetings with friends or family. Transmission aspects, such as decibel range for audio needs to be of high-quality. For calls, industry allows higher audio resolution but still mostly in mono only.

3.2 Bandwidth for video

Scenario: A hard of hearing user needs better stereo sound so they can have a quality experience in watching HD video or having a HD meeting with friends or family. Transmission aspects, such as frames per minute for video quality needs to be of high-quality.

NOTE: EN 301 549 Section 6, recommends for WebRTC enabled conferencing and communication the application shall be able to encode and decode communication with a frequency range with an upper limit of at least 7KHz. More details can be found at Accessible Procurement standard for ICT products and services EN 301 549 (PDF)

NOTE: WebRTC lets applications prioritise bandwidth dedicated to audio / video / data streams; there is also some experimental work in signalling these needs to the network layer as well as support for prioritising frame rate over resolution in case of congestion. [webrtc-priority]