SDH Subtitles vs. Closed Captions: What’s the Difference?

August 24, 2021 BY ELISA LEWIS
Updated: January 26, 2022

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“Tomato, tomahto.” That’s what people might think when seeing the words “subtitles” and “captions,” but, there actually is a difference. Before fully understanding the difference between subtitles for the deaf and hard of hearing (SDH Subtitles) and closed captions, it is helpful to first understand the difference between subtitles and captions.


Subtitles vs. Closed Captions

How are they alike?

Both subtitles and closed captions are synchronized with the media so the text can be viewed at the same time the words are being spoken. Typically, both closed captions and subtitles can be turned on or off by the user.

How are they different?

Subtitles are intended for hearing viewers who do not understand the language. For this reason, subtitles only show the spoken content but not the sound effects or other audio elements. They are usually used to refer to translations, for instance, subtitles for a foreign film.

Closed captions, on the other hand, are meant for deaf and hard-of-hearing audiences. They communicate all audio information, including sound effects, speaker IDs, and non-speech elements. Closed captions are written in the source language of the video. They originated in the 1970s and are required by law for most video programming in the United States.

What Are Subtitles for the Deaf and Hard of Hearing?

SRT file icon So now that you know the similarities and differences between subtitles and closed captions, let’s add one more into the mix.

Subtitles for the deaf and hard of hearing (SDH) are subtitles that combine the information of both captions and subtitles. They can be in the source language of the video, as they include important non-dialogue audio like sound effects and speaker identification. While normal subtitles assume the viewer can hear the audio but doesn’t know the spoken language, SDH assumes that the viewer cannot hear the audio (like with captions). In this case, subtitles for the deaf and hard of hearing are intended to emulate closed captions on media that does not support closed captions, such as digital connections like HDMI. SDH subtitles can also be translated into foreign languages to make content accessible to the deaf and hard-of-hearing individuals who understand other languages.

The Difference Between SDH Subtitles and Closed Captions


Subtitles SDH Closed Captions
Synced with video Yes Yes Yes
Can be turned on/off Yes Yes Yes
In source language Yes Yes
Speaker Identification Yes Yes
Sound effects Yes Yes
Text appearance Varies Varies Usually white text on black background
Onscreen placement Centered lower bottom third Centered lower bottom third Varies
Encoding Supported through HDMI Supported through HDMI Not supported through HDMI


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The Technicalities of SDH Subtitles


Subtitles for the deaf and hard of hearing differ from closed captions in a number of ways. The first difference is in appearance. Closed captions are typically displayed as white text on a black band, whereas SDH subtitles are usually displayed with the same proportional font as translated subtitles. More and more often, however, both subtitles and closed captions have user control options that allow the viewer to change the color, font, and size of the text.

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Subtitles for the deaf and hard of hearing and closed captions also differ in terms of placement. Closed captions can usually be aligned to different parts of the screen, which is helpful for speaker identification, overlapping conversation, and avoiding interference with important on-screen activity. SDH subtitle text is usually centered and locked in the lower bottom third of the screen.


The biggest difference between subtitles for the deaf and hard of hearing and closed captions is that they are encoded differently. While closed captions are encoded as a stream of commands, control codes, and text, subtitles are often encoded as bitmap images – a series of tiny dots or pixels.

The difference between SDH subtitles and closed captions was made particularly apparent by the move from analog TVs to high-definition media. Blu-ray, as well as other HD disc media, do not support closed captioning but will support SDH subtitles.

So while shifting from analog to digital TV gave us a crystal clear picture and uninterrupted sound, it also brought about major difficulties for Closed Captioning (CC).

Enabling CC on an analog TV was simple – the TV did all the CC decoding. With the introduction of digital HDTV services (cable, satellite, etc.) the responsibility of decoding CC was put into the Set-Top Boxes. To make matters more confusing, all of these Set-Top Boxes have different ways of enabling CC. Even though all set-top boxes are required to support CC, the implementation can vary significantly between products, causing a great deal of confusion.

Subtitles for the deaf and hard of hearing provide accessibility for HD disc media. Just as closed captions are beneficial to people who aren’t Deaf or hard of hearing, SDH subtitles make content more accessible to a wide range of people by:

  • Improving comprehension for ESL speakers
  • Helping viewers with attention deficits or cognitive differences focus on the video
  • Helping viewers understand people with thick accents or speech impediments
  • Improving the viewing experience in sound-sensitive environments

It should be noted, however, that subtitles for the deaf and hard of hearing do not satisfy the FCC’s requirements for closed captioning of broadcast video. For this reason, in addition to the ever-changing technology, it seems reasonable to believe that SDH subtitles may become obsolete in the not-so-distant future.

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This post was originally published by Lily Bond on May 21, 2014 as “How Subtitles for the Deaf and Hard-of-Hearing (SDH) Differ From Closed Captions”, and has since been updated for accuracy, clarity, and freshness.

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