You are here: joeclark.orgAccessibilityCaptioningBest practices in online captioning


The present activity is part of the Inclusive Learning Exchange (TILE) project and pertains to “best practices in online captioning.” This report assumes the following parameters and limitations:

Video – and accessibility – on the Web

Use of online video has grown faster than the use of accessibility in online video. Though bandwidth costs for video files can still be high compared to ordinary text-and-graphics Web pages, it is nonetheless easy to digitize video and post it online. It’s easier to broadcast your video to the world via the Internet than it is to get the same video on television. Online multimedia are a useful and valid new medium of communication – for most people.

However, the majority of online video remains inaccessible to blind/visually-impaired and deaf/hard-of-hearing viewers, the latter of which groups are the concern of this TILE activity. The reasons are many:

  1. Shooting, posting, and serving video are relatively easy. Even editing video is easier than it used to be. But captioning has never been easy and has not gotten any easier with the advent of multimedia.
  2. Even if you know how to caption a videoclip or program, it’s technically difficult, and sometimes expensive, to add the captions to the video.
  3. Multiple players, video formats, and text-file types bring about incompatibilities. Your chosen video format may limit what you can do with captions, and in any case your viewers will need a player that can run your video and the captions.
  4. The form of captions – typography, placement, chunking, speed, identification of non-speech information, and other factors – varies widely according to player type. Yet captioners are, at the same time, surprisingly limited in their options for captioning form; authors have much less control than in other captioned media. Of particular interest is the complete absence of fonts that are designed for online captioning and proven to be legible, readable, and usable by viewers.
  5. Authoring tools are hard to use, sometimes unreliable or expensive, and inaccessible to people with disabilities other than hearing impairment. (No captioning software is known to adhere to the Authoring Tool Accessibility Guidelines, for example.)
  6. Web authors who wish to provide captioned video in order to meet the Web Content Accessibility Guidelines may find that certain other browser incompatibilities cause them to violate the Guidelines in some other way. Also, the Guidelines permit Web developers to provide simple transcripts rather than actual captions.
  7. Online captioning is almost exclusively an English-language phenomenon. Captions in other languages are hard to find; character encoding can be unreliable.
  8. There is no easy way to convert captions into transcripts or Web pages with semantic, valid XHTML or similar markup. This has implications for the reuse of captioning in a learning repository.
  9. Most online captioning is closed, using video players’ own formats and functions to hide captioning inside or alongside the video stream. Closed captioning replicates the model used nearly all the time on TV, on video and DVD, and at the movies, but may be unnecessarily complex and expensive much of the time in online captioning.

But the news is not all bad:

  1. There isn’t a lot of captioning online, but there certainly is some.
  2. Some high-profile projects are available with captioning.
  3. Quantities of captioning are increasing slowly.
  4. It is perfectly possible to closed-caption online video in all three major formats, and all video formats can be open-captioned.
  5. Government and industry requirements for captioned video are growing; in those sectors, captioning ceases to be discretionary, resulting in more video with captions.
  6. Transcripts created from captions – preferably with valid semantic markup – are a useful resource for searching and archiving; they give accessible video a second life.