Closed Captioning Standards and Protocol

Table of Contents

Closed captioning remains a standard feature for the video media, whether it"s published online or broadcast on TV. To help the video creators, we have compiled an extensive guide on closed captioning standards and protocol. Read on to learn about guidelines from the different oversight agencies, various closed captioning file formats, and all the rules that you should observe when creating your own captions.

closed captioning standards

What is closed captioning?

Closed captions are often abbreviated as CC. They are the time-synchronized transcription for the full audio track of the video created with an assumption that the viewer cannot hear the audio. Unlike subtitles that only capture the spoken dialogue, closed captions offer textual representation of all the audio elements, including ambient sounds, action sounds (laughter/sneezing/etc), and more – anything and everything that"s important for context understanding. The word "closed" indicates that the viewer can turn the captions on and off.

What are the benefits of using closed captions

While the closed captions were initially invented with the deaf and hard-of-hearing communities in mind, their benefits extend beyond this. There are millions of people who watch videos while commuting or in other situations where playing the audio out loud is not an option, so adding captions to your content provides these viewers with access.

There are other considerations as well, and the most important of them is engagement. According to a Verizon Media study, 80% of consumers say they are more likely to watch the full video if it has captions. So, if you care about viewers watching your videos to the end, make sure to add captions to them.

Choosing between closed and open captions in favor of the former gives your viewers a sense of control, because they are the ones who make the decision to turn them on or off.

For organizers of webinars and online conferences, closed captions are an important tool that ensures that the audiences can fully understand all the speakers, regardless of the speaker"s accent or complexity of the topic.

Finally, uploading a file with captions along with your video content is a great way to improve your SEO performance. Captions make such videos searchable by engines such as Google, Bing, and others – and captioned videos will naturally rank higher than their uncaptioned counterparts.

Сlosed Сaptioning Guidelines

In the US, there are several agencies/organizations that set the guidelines and standards for the use of captions. Here is what you need to know.


closed captioning guidelines

The Described and Captioned Media Program (DCMP) is funded by the US Department of Education. It provides services and content that are designed to support and improve academic performance of students with sensory disabilities. The program partners with educational and television content creators to make media accessible to these students. DCMP requirements for captioning of such videos are as follows:

  • Accurate – The captions must be without errors.

  • Consistent – The presentation and style of captions must be uniform to ease viewer comprehension.

  • Clear – The captions must represent all forms of audio, including dialogue, noises, and other non-speech sound elements.

  • Readable – The captions must not conceal the visual content and mirror the audio, while making sure that enough time is given to viewers to read the text. The presentation rate should range from 120-130 words per minute (wpm) for lower- to middle-level educational videos to 150-160 wpm for adult special interest movies. No captioning should exceed 225 wpm.



The Federal Communications Commission (FCC) is a US government agency that regulates communications by radio, television, wire, satellite, and cable. The FCC enforces Title II of the Americans with Disabilities Act (ADA) of 2011. The ADA requires all public entities to "take appropriate steps to ensure that communications with applicants, participants, members of the public, and companions with disabilities are as effective as communications with others." The FCC guidelines for captions read as follows:

  • Accurate – Captions must present an accurate version of the audio track, including dialogue, background noises, and other sounds. They must also correctly identify the speakers.

  • Synchronous – The captions must sync up to the audio and be of the correct length for the viewers to read.

  • Complete – The captions must cover full content of the video, from beginning to the end.

  • Properly placed – The captions should not obstruct the video on the screen or overlap with other captions.



The Web Content Accessibility Guidelines (WCAG) are published by the Web Accessibility Initiative (WAI) of the World Wide Web Consortium (W3C), which is the main international standards organization for the internet. They are aimed at improving accessibility of Web content, primarily for people with disabilities. The WCAG captioning guidelines require that the captions are:

  • Operable – The captions should be accessible with a keyboard.

  • Understandable – The text on the screen must be legible, without obscuring important visual elements and with appropriate color contrast ratio.

  • Perceivable – The captions should support the presentation of text through screen readers/assistive technologies, making it possible to convert the text to audio or braille version.

  • Complete – The captions must describe all important sounds, including background noise, sounds of actions, or meaningful musical cues.


Closed Caption File Formats

When it comes to captions, there is a whole range of file formats to choose from. We"ll list the most common formats below, but remember that adherence to caption requirements is more important than the format you use. That said, here are some of the widely-used file formats:

  • .SRT (SubRip) – this is a plain text file format. It is also by far the most commonly used. It contains only the caption text with start and end timecodes. SRT files can be created with plain-text editors, such as Notepad or TextEdit. They are compatible with all major social media platforms, as well as YouTube, Amazon, Vimeo, and Netflix.

  • .SBV or .SUB (SubViewer) – this is also a plain text caption file format. It is most often used for adding captions or subtitles to YouTube videos. Includes start and end timestamps for each caption.

  • .VTT (WebVTT) – this file format, which stands for Web Video Text Tracks, is widely compatible with the major platforms. It is based on the SRT format and easy to use. What distinguishes VTT format from SRT is that the former can store metadata and other descriptions (such as caption placement on the screen) in addition to the caption text.

  • .DXFP (Distribution Format Exchange Profile) – this type of caption file contains the captions in XML format. DFXP files are compatible with YouTube, Vimeo, Netflix, and all Adobe products, as well as Microsoft Silverlight. In addition to the caption text and timestamps, such files contain information about formatting and caption location specifications.

  • .SCC (Scenarist Closed Caption) is one of the oldest file formats. It was initially created for analog TV, VHS and DVD formats. Today, this format is used on platforms such as iTunes, Netflix, and Amazon. Such files include the caption text, timings, and details on the look and placement of captions.


Closed Captioning Style Guide

In addition to the general requirements, captioning must follow a number of rules that pertain to grammar, correct line breaks, and more. Here is the rundown of everything that you need to know when creating your captions.

First, the general rules:

  • The line of caption text should be 32 characters or less, including spaces.

  • There should be no more than one or two lines per screen. Anything greater than that makes it hard to read.

  • Do not use all caps, unless you want to show that the speaker is screaming.

  • Use a font with average thickness, nothing too thick or too thin.

  • Caption text should be centered on the screen and aligned to the left.


Grammar and Line Breaks

As a caption line should not exceed 32 characters, you will have to create line breaks. Here are the rules that will help you preserve the correct grammar and clarity of your captions.


A modifier is an option element in phrase structure that modifies the meaning of another element. Adjectives and adverbs are modifiers. The rule of thumb is not to separate modifiers from the words they modify.



Ella wrote 
her farewell letter.
Ella wrote her farewell 

Prepositional Phrases

A prepositional phrase is a group of words that begins with a preposition (about, for, from, of, on, out – and many more) and ends with a noun, pronoun, or noun phrase. Do not break the prepositional phrases in your captions.



The dog went 
out of the house.
The dog went out 
of the house.

Name or Title

If the caption text contains a person"s full name or title (Edith Baker, Professor Smith, Detective Hastings), do not break them between two lines.



John and Janet Spencer 
are in the garden.
John and Janet 
Spencer are in the garden.


A conjunction is a part of speech that connects words, phrases, or clauses. The most common conjunctions are and, if, as, so. The rule here is not to put a line break immediately following a conjunction.



She entered the room, 
and everyone looked at her.
She entered the room, and 
everyone looked at her.

Verb Phrases

A verb phrase consists of the main verb and its auxiliary or helping verbs. When creating captions, do not separate the auxiliary verb from the word that it modifies.



Simon said I should have been 
more careful.
Simon said I should 
have been more careful.


Never end a sentence and begin a new sentence on the same line. This can only be done if the sentences in question are very short (1-2 words) and related.



I went to the window 
and looked out.
I went to the window and 
looked out. It was

Sound Effects and Music

captioning sound effects

Unlike subtitles, captions must convey the full audio track, because sounds other than the dialogue may be important to understanding the video. The following practices are recommended for captioning sound effects:

  • Unless the source of the sound can be clearly seen on the screen, it should be included within brackets to help the viewers identify it.

  • The sound can be either described or spelled out with onomatopoeia. Common onomatopoeias include animal noises such as oink, meow, road, and chirp.

  • Sound effect captions are done in all lowercase letters.

  • Offscreen sound effects should be written in italic.

  • If you are captioning music, add musical note icons at the start and end of the caption.

  • If the music has lyrics, caption the lyrics verbatim and add musical note icons at the start and end of the lyrics.

  • When a song begins, introduce the lyrics with the name of the artist and the song title in brackets.


Speaker Identification

Speaker identification is an important prerequisite of captions as it helps to maintain clarity. When creating captions, you must identify the speakers, both on-screen and off-screen. If the speaker is off-screen, you should use italics and [offscreen] to indicate this.

Whenever someone starts speaking, the caption must begin with their name. If the name of the speaker is unknown, use other labels such as "NARRATOR", "WOMAN 2" or "POLICEMAN" to provide identification. Speaker IDs can be done as all caps or in parenthesis. Whichever option you choose, be consistent.

Final thoughts

In addition to being mandatory for most of today"s content, closed captions are a useful tool for expanding your audience and increasing engagement. So, don"t treat them as an afterthought. Luckily, the progress that has been made by AI-powered platforms, such as vidby, enables creators to shift the burden of creating captions to the "shoulders" of machines. Just remember to always check your captions before publishing them, both for accuracy and adherence to caption guidelines, because you want to provide the best experience for your viewers.

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