How Subtitles for the Deaf and Hard-of-Hearing (SDH) Differ from Closed Captions
In order to fully understand the difference between subtitles for the deaf and hard-of-hearing (SDH) and closed captions, let’s first explore the how subtitles and closed captions are not the same thing.
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 spoken. Closed captions and usually subtitles can be turned on or off by the user.
How are they different?
Subtitles are intended for viewers who can hear the audio, but cannot understand the language. They communicate the spoken content but not the sound effects. They are usually used to refer to translations, such as subtitles on a foreign film.
Closed captions, on the other hand, communicate all audio information, including sound effects, speaker IDs, and non-speech elements. They are written in the source language of the video. They originated in the 1980s and are required by law for most video programming in the United States.
What Are Subtitles for the Deaf and Hard-of-Hearing?
SDH are subtitles in the source language of the video that also include important non-dialogue audio sound effects and speaker identification. While normal subtitles assume the viewer can hear the audio but doesn’t know the spoken language, SDH assume that the viewer cannot hear the audio (like with captions). They are intended to emulate closed captions on media that does not support closed captions, such as Blu-ray.
The Difference Between SDH and Closed Captions
Subtitles SDH Closed Captions Synched with video Can be turned on/off In source language Speaker Identification Sound effects 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 (Blu-ray or HD DVD) Supported through HDMI (Blu-ray or HD DVD) Not supported through HDMI (Blu-ray or HD DVD)
SDH differ from closed captionsin a couple of ways. The first difference is in appearance. Closed captions are traditionally displayed as white text on a black band, while SDH subtitles are usually displayed with the same proportional font of translation 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.
SDH 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 text is usually centered and locked in the lower bottom third of the screen.
The biggest difference between SDH and closed captions is that they are encoded differently. Certain high-definition media, including Blu-ray and HD DVDs, do not support closed captioning. In fact, any disc playing through an HDMI connection will not play closed captioning, but will support SDH subtitles.
While closed captions are encoded as a stream of commands, control codes, and text, subtitles are often encoded as bitmap images. This makes it much harder to decode the subtitles back into text form or to convert them into other formats, whereas it is generally easy to do so with closed captions.
Just as closed captions are used by people who aren’t deaf or hard of hearing, SDH subtitles provide accessibility to a wide range of people:
- They improve comprehension for ESL speakers
- They help viewers with attention deficits or cognitive differences focus on the video
- They help viewers understand people with thick accents or speech impediments
- They improve the viewing experience in sound-sensitive environments
It should be noted that while SDH do provide accessibility for HD disc media, they do not currently satisfy the FCC’s requirements for closed captioning of broadcast video.
The FCC put out an order in June, 2013 requesting comment on the possibility of reconsidering this ruling, but a decision has not yet been made as to whether SDH will satisfy the FCC’s requirements moving forward.
Subtitle File Formats
Some subtitle file formats are text-based, while others are image-based. Text-based subtitle formats include SubRip SRT, WebVTT, iTunes iTT, PAC, DLP Cinema XML, and EBU-STL. Image-based (or “bitmap subtitles”) include Blu-ray BDN, UYC/USF, and any other format that includes image files like PNG, TIFF, or BMP.
A common way to add SDH to Blu-ray is to create a BDN.xml file, along with PNG (image) files.
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