Skills for Access

Why this is important

Video content that contains spoken or other audio information (for example on-or off-screen sound effects, or background music) that is important to understanding the video's content will present access barriers to anyone who is deaf or hard of hearing and unable to hear the video's soundtrack. The same problem will also be encountered by anyone accessing the video using a computer without a soundcard and/or speakers, or in a noisy environment, or where no sound is permitted. Therefore an alternative to the information provided in audio format is required to make the media accessible to these groups.

General Principles

There are two accessibility solutions for this barrier: the first, and easiest, is to provide a text transcript in HTML. For audio content with no visual output, a transcript will suffice - although it is eminently possible to caption audio files. However for video, the alternative, most equitable, and therefore most desirable accessibility solution is to go a step further and provide the video with text captions for all spoken and other audio content.

NB Avoid confusing 'captions' with 'subtitles'! Subtitles is a term used widely in the UK - including by Ofcom and the BBC - to refer to any text alternatives displayed alongside a television program, video or DVD. But from an accessibility standpoint 'subtitling' actually refers to a translation of the spoken content into another language. In other words, subtitles are an accessibility solution for people whose first language is not that of the video. They only replace spoken content, and do not provide alternatives for other sounds.

Before you continue

The advice on this page helps you avoid introducing a specific accessibility barrier, but it's not a magic formula. To avoid attempting to follow a technical solution that is not appropriate to the resource and its intended purpose, you need to know the context in which the multimedia resource is being used:

1. The purpose or aim of the multimedia resource in question, and whether it is being used to supplement another resource in the learning environment, or whether its use is required by students.
2. The target audience, their knowledge and expectations, and the type of browsing and assistive technology that they may be using.
3. Whether the information and experiences provided by the multimedia technology are already available in an equivalent, alternative form.

For more background on this approach, see our Guide to the use of multimedia in accessible e-learning.

Technique Details

Providing captions is a two-stage process. The first, and most challenging and resource intensive stage, is to generate a textual transcript of all spoken content of the video, plus additional important non-spoken audio information (discussed separately in How To Provide text equivalents for audio - general advice on transcripts).

Once you have a transcript, you must break it down into appropriate chunks such that it can be synchronised with the video content; timestamp each caption such that it appears at the appropriate point as the video plays, and include the caption file with the video file.

The 'chunking', knowing what to include and what can be left out, and knowing how to present the captioned information is a skill in its own right as it is impossible to convey the totality of information in captions, especially as they must keep pace with the action. Guidelines for captioning do exist, and should be reviewed - see External Resources. Be aware though that as captioning is something of an 'art', different sources take different approaches.

Styling is also an important aspect of effective captioning - as well as the use of punctuation marks to convey meaning within the caption text, the text size, colour (and changes in colour) and font used can have an impact on the effectiveness of the captions. Unfortunately, current player support can cause problems for caption display. For example if the caption display area is not appropriately sized, some caption text may disappear off the edge of the area; if a font is specified but not present on an end user's machine, unpredictable results may occur.

Experts recommend that if you are planning on captioning video, that you become familiar with the use of captions - in the UK the best way to do this is spend some time watching TV with captions (subtitles) turned on (888 for Ceefax/Teletext, or for digital TV, turn on subtitles using the set-top box remote control).

There is a variety of techniques for adding synchronised captions to a video - each main video format/player enables captions to be added using its own proprietary format, while stand-alone software such as MAGpie also allows creation of caption files. The World Wide Web Consortium (W3C) technology SMIL (Synchronised Multimedia Integration Language) offers an open standard for creating accessible media files, including captions and audio description. Each technique is discussed in a separate How-to.

Given that there are some challenges in creating and making available captions and audio descriptions in multiple media players, rather than providing 'closed' captions and descriptions ready to be turned on by the user, in some cases the best solution may be to provide separate 'accessible' versions of the media:

1. Video plus audio
2. Captioned video plus described audio
3. Described audio as a sound file (for example MP3)

Testing

Though guidelines do exist, captioning is a highly subjective activity, thus making it impossible to test using automated means. The process of creating a captioned video is also often lengthy and iterative, but as a result has a degree of in-built quality control, as it requires constant reviewing of presentation and timing. Once available on the web, playing the captioned resource in as many different platforms as possible is recommended. Feedback from end users is also highly recommended, particularly people who are deaf or hard-of-hearing.