Sdh or Captions? Subtitles for Digital Accessibility

Janaina Santos, 06 October 2020

sdh and closed captions


If you are interested in captions and subtitles, you probably know that the difference between captions and subtitles is: the first assumes that the viewer cannot hear the audio while the second assumes that they can hear it but not understand it.
Considering this, which one is the best for digital accessibility: Sdh (subtitles for the deaf and hard of hearing) or closed and open captions?

Differences in technology

Media types such as Blu Ray and DVDs do not support the same type of captions you will find on most televisions shows and broadcasts. That is because closed captions are not compatible with HDMI ( High Definition Media Interface) but SDH are.

There is also a difference in terms of how the SDH and captions are encoded in a video file, with the first being burned as images, dots or pixels, and the latter as commands, codes or text.


Most SDHs do not allow positioning, so you will find them centred in the lower bottom third of the screen. However, they do allow personalization of styles, colors and font sizes, which is not something you will see with closed captions ( usually displayed in white over a dark background).

closed captions

Example of closed caption


Example of non-speech information in SDH (source)

Which one should you use for Digital Accessibility? Captions or SDH?

According to the Web Content WCAG 2.1, every video posted online needs to offer captions or a text version. The requirements specify, among other things, the inclusion of important sounds besides the dialogue. That means that closed captions and SDHs could both be used to meet the accessibility standards but not regular subtitles.

Read more: Digital Accessibility and the WCAG standards.

Do you need to create SDH subtitles or captions?

Creating subtitles for Digital Accessibility

Automatic Speech Recognition is a powerful ally of Digital Accessibility as it makes the process of creating transcripts and subtitles faster and more affordable.

Technology has advanced enormously in this field but the results will be around 80% accurate if you are using an automatic tool like Amberscript and the quality of the audio is good. That means you need to make adjustments in the final files to use it for Digital accessibility purposes, making sure that the timestamps are matching the video file and correcting minor spelling mistakes in the online editor.

By using an automatic tool, you will be saving hours of your time in comparison to creating the subtitles or transcriptions from scratch.

How to create subtitles – a Step by Step Guide

If you have a large volume of audio and video or simply need to outsource the final edits, you can request a service where the subtitles are fully edited and perfected by language experts, such as the manual subtitling service provided by Amberscript.

Watch the webinar about Digital Accessibility and the legislation


  • Captions assume viewers can’t hear the audio while subtitles assume they can hear it but not understand it – therefore this term is more associated with translations.
  • SHD subtitles were created by the DVD industry to include the description of sounds that give content to the dialogue.
  • SHD differs from closed captions in appearance, positioning but also on the technology it supports – captions are not compatible with HDMI.
  • For Digital Accessibility purposes, you can use sdh or closed captions but not regular subtitles as it should be possible to understand the context without hearing the sound. You can find the full guidelines here.
  • If you need to create SDH subtitles or captions for your videos, Amberscript can help you!

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