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SDH Subtitles vs Closed Captions (CC)

Although the terms “captions” and “subtitles” can sometimes be used interchangeably, they actually fulfil different functions.

In places like the United Kingdom, the term “subtitles” refers to both subtitles and captions. However, in the United States and Canada, they represent two quite different things. From here on out, we’ll discuss these terms as defined in the US and Canada.

So, how are captions and subtitles actually different? And are subtitles the same thing as subtitles for the deaf or hard of hearing?  

Let’s address the similarities and differences between subtitles, closed captions, and subtitles for the deaf and hard of hearing and when they should be used.

What Is the Difference Between Captions and Subtitles?

The main similarity between captions and subtitles is that they are both timed text files synchronised to a piece of media content. This allows a viewer to read the text simultaneously as the words are spoken on the screen. However, captions and subtitles have different aims.

Captions (aka closed captions or CC) are in the same language as the video, and they’re generally intended for people who are deaf or hard of hearing. They are also helpful to people with cognitive impairments who have difficulty processing auditory information or prefer textual over auditory information.

In addition, they can be extremely useful to people who can't listen to or hear the audio due to being in circumstances that are particularly noisy (such as airports or restaurants) or particularly quiet (such as a library, home at night, etc.)

Since closed captions assume that the viewer can’t hear the audio, they also include relevant auditory information - music, song lyrics, sound effects, loud noises, and non-verbal sounds (e.g., people laughing, crying, etc.)

When necessary, speaker names are also included (e.g., when a person speaks off-screen). They may also include the tone of delivery (e.g., whispering) if it’s essential to understand the context of a scene.

They will not include on-screen text and narrative titles (such as a “help wanted” sign or a “one year later” chyron.

On the other hand, subtitles are primarily intended for hearing viewers who don’t understand the language in the video. They are used to translate the audio from another language (e.g., English-speaking viewers watching a Spanish video).

Since subtitles come with the presumption that the viewers can hear the audio, they do not include music, sound effects, loud noises, and non-verbal sounds. They will, however, include translations of on-screen text and narrative titles. Note that the translation of dialogue generally takes priority, so on-screen text and narrative titles will only be included if there’s enough time between the lines of dialogue.

Closed Captions vs Subtitles

What Is the Difference Between Closed Captions (CC) and SDH Subtitles?

Subtitles for the deaf and hard of hearing are also known as SDH subtitles or HI subtitles (Hearing Impaired subtitles). They are not the same as subtitles or captions as described above.

Similarly to captions, SDH subtitles assume that a viewer cannot hear the audio, so they will also include pertinent auditory information typically only included in captions, including music, song lyrics, sound effects, on-screen text, and narrative titles, time permitting.

Thus, SDH subtitles serve the same function as captions on types of media that do not support closed captions.

SDH subtitles can also be translated into foreign languages, making content accessible to deaf and hard-of-hearing individuals who speak other languages (e.g., Spanish in the US and Quebec French in Canada).

However, there are additional differences between closed captions and SDH subtitles:


Closed captions are, usually as a default, displayed as white text against a black background. The older analog television transmissions standard CEA-608 uses the more typical white text against a black background. Due to their compatibility with digital television, they’re still widely used today.

The newer CTA-708 closed captioning standard for digital television transmissions in the US and Canada does allow for some user customisation options. However, these options may vary depending on a particular TV model and other equipment.

On the other hand, the appearance of SDH subtitles varies and has more flexibility than closed captions. They allow for a variety of font, size, and colour options. They can be made to look like closed captions or to match the specifications of a platform or requests of a viewer.

However, these customisation options also depend on a particular TV model, media player, streaming service, or other platform, so they do not apply to every viewer in every situation.


Another difference between closed captions and SDH subtitles is the character-per-row limit. The limit for closed captions is up to 32 characters per row, while the limit for SDH subtitles is 42.

Due to this considerable difference, transcription of SDH subtitles is more accurate because it can include additional information that closed captions simply cannot because of the character limit.

In addition, closed captions have to be timed tighter to the audio than SDH subtitles. That can also allow for more verbatim dialogue transcription in the case of SDH subtitles and lead to improved accuracy over closed captions.  


The position of closed captions on the screen can vary and is typically implemented by a professional captioner (other than those formatted to CTA-708 standard). They can be centred on the bottom of the screen and to the left or right side of the screen to match the speaker's position in the shot. They can also be placed at the top of the screen so as not to cover any critical lower-third narrative titles or on-screen text.

SDH subtitles, however, usually appear centred and locked on the bottom of the screen (same as subtitles) for the purpose of easy readability and translation.  


On a more technical level, closed captions are encoded as a stream of commands, control codes, and text, whilst SDH subtitles are encoded as bitmap images, i.e., a series of tiny dots or pixels.

What that means in layman's terms is that closed captions are not supported through digital connections such as HDMI (High-Definition Multimedia Interface) but typically through Teletext. However, SDH subtitles are supported by HDMI and streaming videos, allowing them more variety in terms of their practical applications.

How to Use SDH Subtitles

Though closed captions and SDH subtitles have the same goal of making content accessible to people with hearing impairments, they have different characteristics, advantages, and disadvantages. Choosing which one to use may depend on the specific requirements and regulations of each country, as well as the preferences of each user.  

Some streaming services, such as Apple TV+ offer a choice between closed captions and SDH subtitles on select programming, allowing every subscriber to choose their preferred way of watching the content. Some services like Netflix can’t support standard broadcast closed captions, so they must provide English SDH subtitles for their users.

As mentioned above, due to being supported by HDMI and streaming platforms, SDH subtitles are compatible with physical media discs such as Blu-rays and 4K UHD Blu-rays, as well as with streaming services and video-on-demand platforms. Providing SDH subtitles ensures fuller accessibility to a broader audience.

SDH subtitles can also be used for virtual event recordings, training and corporate communication videos, and open online courses. SDH subtitles also make translations easier, helping to remove communication barriers for employees or students worldwide.

Including subtitles, captions, or SDH subtitles in your media files ensures your content will reach as broad an audience as possible. They not only make content accessible to people with hearing and cognitive impairments, but they also provide a more convenient and satisfying user experience for everyone.

Subtitles, captions, and SDH subtitles also help your content become more discoverable by improving your Search Engine Optimisation (SEO), as they help search engines like Google better analyse your content and increase the traffic to your website.

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