Introduction

Methods of making video and audio accessible

There are four main methods of making video and audio accessible to audiences with sensory disabilities (deaf or hard of hearing, blind or low vision, and deafblind):

  • Captions: Text synchronized with the media, for people who cannot hear the spoken words.
  • Transcripts: The full text of the spoken words and important visual information in the media file, to read as an alternative to watching or listening to the media file.
  • Audio descriptions: A version of the media file with a narrator explaining important visual information (such as unspoken actions and events) for the benefit of people who cannot see what's happening.
  • Sign language interpretation: Video of an interpreter, synchronized with the media file (or in the same video frame), for the benefit of people who know sign language.

There are additional considerations:

  • Clear audio: Prominent background sounds make it difficult for people who are hard of hearing to understand the spoken words.
  • Preventing seizures: Flashing visual effects in videos can cause seizures in some people.
  • Preventing dizziness: Some people with vestibular disorders can become dizzy, nauseous, or disoriented when there is excessive motion in video or animated content.
  • Accessible media player: The media player itself has to be keyboard-accessible and needs to communicate the names, roles, and values of the controls and the states of the controls.
  • Preventing auto-play audio interference with screen readers: Media players that auto-play can interfere with screen reader users' ability to hear their screen reader.

Summary

Four main methods of making video and audio accessible:

  • Captions: Text synchronized with the media, for people who cannot hear the spoken words.
  • Transcripts: The full text of the spoken words and important visual information in the media file, to read as an alternative to watching or listening to the media file.
  • Audio descriptions: A version of the media file with a narrator explaining important visual information (such as unspoken actions and events) for the benefit of people who cannot see what's happening.
  • Sign language interpretation: Video of an interpreter, synchronized with the media file (or in the same video frame), for the benefit of people who know sign language.

Additional considerations:

  • Clear audio: Prominent background sounds make it difficult for people who are hard of hearing to understand the spoken words.
  • Preventing seizures: Flashing visual effects in videos can cause seizures in some people.
  • Preventing dizziness: Some people with vestibular disorders can become dizzy, nauseous, or disoriented when there is excessive motion in video or animated content.
  • Accessible media player: The media player itself has to be keyboard-accessible and needs to communicate the names, roles, and values of the controls and the states of the controls.
  • Preventing auto-play audio interference with screen readers: Media players that auto-play can interfere with screen reader users' ability to hear their screen reader.

Multimedia Accessibility Decision Matrix

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Captions

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When Captions Are Needed

  • Prerecorded multimedia (video plus audio) files MUST include synchronized captions.
  • All live multimedia (video plus audio) events that contain dialog and/or narration MUST be accompanied by synchronized captions.
  • All live audio-only content that contains dialog and/or narration SHOULD be accompanied by text-based synchronized captions.

What to Include in Captions and Transcripts

  • Captions MUST be verbatim for scripted content (except when intentionally creating simplified captioning for a relevant target audience, e.g. people with cognitive disabilities).
  • Transcripts MUST be verbatim for scripted content.
  • Captions and transcripts SHOULD be verbatim for unscripted or live content (with the optional exception of stuttering or filler words -- like "um" -- when captioning the filler words reduces reading comprehension of the captions or transcript).
  • Important visual events MUST be described in the transcript.
  • Important background sounds MUST be conveyed in captions and transcripts, preferably in [brackets] or (parentheses).
  • Speech that is spoken off-screen MUST be captured in captions and transcripts.
  • The identity of the person speaking MUST be identified in captions and transcripts.
  • Captions and transcripts SHOULD use punctuation to convey emphasis whenever possible, rather than write extra text to explain the emphasis.
  • Captions SHOULD use conventional spelling, rather than attempt to write words phonetically, except when phonetic spelling is essential to the meaning of the content.
  • Captions and transcripts MUST NOT reveal intentionally-withheld information in the content before the appropriate time.
  • Music SHOULD be identified by title and artist whenever possible in captions and transcripts, unless doing so would be inappropriate to the content.
  • Important music lyrics SHOULD be included in captions and transcripts, if relevant to the meaning of the content.
  • When speech is inaudible or difficult to perceive clearly, captions and transcripts SHOULD say so, using neutral language.
  • Strong language SHOULD be retained and not edited out of captions and transcripts, whenever possible, OR SHOULD be bleeped or muted to match style or content requirements of the intended audience or context.
  • Captions and transcripts SHOULD indicate when speech is whispered or mouthed.
  • Captions SHOULD describe sounds in terms of the sounds themselves, not the actions causing the sounds.

Visual Presentation of Captions

  • Captions SHOULD NOT exceed three lines on the screen at a time.
  • Caption line breaks, when necessary, SHOULD be inserted at logical points between phrases, rather than in the middle of a phrase.
  • Captions SHOULD be typed in mixed case.
  • The default font for captions SHOULD be a sans-serif font.
  • The maximum number of characters per line of captions SHOULD NOT exceed 32 characters.
  • Captions SHOULD remain on the screen for a minimum of 1 second under all circumstances, AND SHOULD take into account the number of words, at 0.3 seconds per word, if possible.
  • Captions SHOULD be positioned to not obscure on-screen text, people's faces, or other important visual information.
  • Captions SHOULD be precisely synchronized to the audio, except when doing so would make captions difficult to read.
  • The default color combination SHOULD be white text on a black background.
  • The default caption font color and background MUST be a minimum of 3:1 (assuming a minimum font size of 18 point).
  • The default font size for captions SHOULD be at least 22pt.
  • The default font weight for captions SHOULD be normal (not bold).
  • Colors in captions MUST not be used as the only way to convey meaning.
  • Italics or all caps MAY be used for emphasis in captions when punctuation alone does not convey the full meaning.
  • Quotation marks (or optionally italics or underline, if supported in the caption format) and mixed case capitalization SHOULD be used to designate titles (e.g. of books or movies) when appropriate in captions.
  • The last caption frame SHOULD be removed from the screen during long silent intervals.
  • Any gaps in captions SHOULD be a minimum of 1.5 seconds.
  • Periods of silence SHOULD be noted as such when the visual content gives the impression that there may be important sounds or speech.
  • Additional on-screen time for a caption frame SHOULD be added when the caption contains unfamiliar or uncommon words or phrases.
  • Additional on-screen time for a caption frame SHOULD be added when there is a lot happening visually on the screen.

Visual Customizability of Captions

  • Users SHOULD be able to customize the visual appearance of captions.

Caption File Format

  • Multiple caption file formats SHOULD be provided.
  • At least one of the file formats SHOULD be in a WebVTT file format.

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  • Complete dialog, whom is speaking and non speech info

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Transcripts

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When Transcripts Are Needed

  • A text transcript SHOULD be provided for multimedia (video plus audio) content.
  • Prerecorded audio-only content MUST be accompanied by an easily-reachable text transcript.
  • A text transcript describing the visual aspects of the video SHOULD be provided for video-only content.

What to Include in Captions and Transcripts

  • Captions MUST be verbatim for scripted content (except when intentionally creating simplified captioning for a relevant target audience, e.g. people with cognitive disabilities).
  • Transcripts MUST be verbatim for scripted content.
  • Captions and transcripts SHOULD be verbatim for unscripted or live content (with the optional exception of stuttering or filler words -- like "um" -- when captioning the filler words reduces reading comprehension of the captions or transcript).
  • Important visual events MUST be described in the transcript.
  • Important background sounds MUST be conveyed in captions and transcripts, preferably in [brackets] or (parentheses).
  • Speech that is spoken off-screen MUST be captured in captions and transcripts.
  • The identity of the person speaking MUST be identified in captions and transcripts.
  • Captions and transcripts SHOULD use punctuation to convey emphasis whenever possible, rather than write extra text to explain the emphasis.
  • Captions SHOULD use conventional spelling, rather than attempt to write words phonetically, except when phonetic spelling is essential to the meaning of the content.
  • Captions and transcripts MUST NOT reveal intentionally-withheld information in the content before the appropriate time.
  • Music SHOULD be identified by title and artist whenever possible in captions and transcripts, unless doing so would be inappropriate to the content.
  • Important music lyrics SHOULD be included in captions and transcripts, if relevant to the meaning of the content.
  • When speech is inaudible or difficult to perceive clearly, captions and transcripts SHOULD say so, using neutral language.
  • Strong language SHOULD be retained and not edited out of captions and transcripts, whenever possible, OR SHOULD be bleeped or muted to match style or content requirements of the intended audience or context.
  • Captions and transcripts SHOULD indicate when speech is whispered or mouthed.
  • Captions SHOULD describe sounds in terms of the sounds themselves, not the actions causing the sounds.

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  • Via a link or inpage
  • Must be equivalent information

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Audio Descriptions

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When Audio Descriptions Are Needed

  • Prerecorded multimedia (video plus audio) MUST include audio descriptions.
  • Prerecorded video-only files MUST include audio descriptions.
  • Audio descriptions MAY be provided for live multimedia (audio plus video) content.
  • Audio descriptions MAY be provided for live video-only content.

Extended Audio Descriptions

  • Where pauses in foreground audio are insufficient to allow audio descriptions to convey the sense of the video, extended audio description SHOULD be provided for all prerecorded multimedia (video plus audio) content.

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  • Narrator + complete dialog, whom is speaking and non speech info

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Sign Language Interpretation

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Sign Language Interpretation

  • Determining When Sign Language Interpretation is Needed
  • Sign language interpretation MAY be provided for prerecorded multimedia (video plus audio).
  • Sign language interpretation MAY be provided for prerecorded audio-only content.
  • Sign language interpretation MAY be provided for live multimedia (video plus audio) content.
  • Sign language interpretation MAY be provided for live audio-only content.

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Media Player Accessibility

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Keyboard Accessibility

  • All functionality of a media player MUST be available to keyboard users

Screen Reader Accessibility

  • All controls of a media player MUST present the correct names, roles, and values to screen reader users.

Captions, Transcripts, and Audio Descriptions

  • Media players SHOULD allow users to access captions, transcripts, and audio descriptions.

Customizability

  • Media players SHOULD allow visual customization of captions.
  • Media players SHOULD remember user preferences.
  • Media players SHOULD allow full screen video.

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Tips & Tricks

  • Ensure access to, through and past all embedded content
  • WCAG 2.1.2 No keyboard trap
  • Include labels, instructions recommended
  • All controls keyboard accessible
  • Name, state, Role, value
  • Cross browser / platform testing
  • Ensure captions

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Background Sounds

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Background Sounds in Media

  • Background sounds in prerecorded audio-only and prerecorded multimedia content SHOULD be minimized (20dB lower than foreground sounds, except for occasional sounds of no more than 2 seconds) or eliminated during narration or dialog, or a method must be available to turn off background sounds.
  • Background sounds in live audio-only and live multimedia content SHOULD be minimized (20dB lower than foreground sounds, except for occasional sounds of no more than 2 seconds) or eliminated during narration or dialog, or a method must be available to turn off background sounds.

Background Audio on Web Pages

  • A mechanism MUST be provided to stop, pause, mute, or adjust volume for audio that automatically plays on a page for more than 3 seconds.

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Seizure-Inducing Flashes

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Flashing Content

  • A page MUST NOT contain content that flashes more than 3 times per second unless that flashing content is sufficiently small, the flashes are of low contrast, and do not violate general flash thresholds.

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Animations and Motion

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Parallax Effects

  • Parallax effects SHOULD be kept to a minimum, in terms of the total number of parallax effects, the amount of parallax within each individual effect, and the size of the area affected.
  • All content and features within parallax scrolling content MUST be accessible by keyboard.
  • The contrast of the text against all parts of a moving background MUST be a minimum of 4.5 to 1 for small text or 3 to 1 for large or bold text.

Background Videos and Animations

  • Important content MUST NOT be conveyed through background videos and animations, unless users have full control over playback, and full access to any required captions, transcripts, and audio descriptions.
  • A method MUST be provided to pause, stop, or hide any background videos or animations that begin playing automatically and which last 5 seconds or more.
  • A method SHOULD be provided to pause and restart background videos and animations.
  • The contrast of the text against background videos and animations MUST be a minimum of 4.5 to 1 for small text or 3 to 1 for large or bold text.
  • Movement within background videos and animations SHOULD be minimal.
  • Background videos and animations SHOULD NOT contain sounds.

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Auto-Play

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Auto-Play

  • A method MUST be provided to pause, stop, or hide any media content that begins playing automatically and which lasts 5 seconds or more.

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  • Ends within three seconds

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