<video> elements must have a <track> for captions
How to Fix the Problem
Ensure all video elements have a caption using the
track element with caption attribute. Ensure the caption conveys
all meaningful information in the video element; this includes,
but is not limited to, dialogue, musical cues, and sound effects.
Good captions not only include dialogue, but also identify who is speaking and include non-speech information conveyed through sound, including meaningful sound effects.
The following code shows how to add two different tracks - one in English and one in Spanish:
<video width="300" height="200">
<source src="myVideo.mp4" type="video/mp4">
<track src="captions_en.vtt" kind="captions" srclang="en" label="english_captions">
<track src="captions_es.vtt" kind="captions" srclang="es" label="spanish_captions">
</video>Note:
Captions and subtitles are not the same thing. Captions are necessary for deaf viewers to understand the content. Captions include a text description of all important background noises and other sounds, in addition to the text of all dialog and narration. Subtitles are generally language translations, to help listeners understand content presented in a language they don't understand. A Spanish video file could contain English subtitles, for example. Subtitles generally include only dialog and narration.
Given these differences, you should specify kind="captions" for
deaf access, and not kind="subtitles".
The src attribute gives the name of the track file. The
kind attribute describes the contents of the file. The
srclang attribute specifies the language of the track file using
the appropriate HTML language code. The label attribute provides
a name for the track. None of these attributes, aside from src,
are required. Nevertheless, they are highly recommended because they increase
clarity.
Youtube offers automatic captioning as a somewhat experimental feature. The automatic captions tend to be too inaccurate to use without some editing, but it gets rid of quite a bit of work. Another useful feature offered by YouTube is the ability to synchronize a transcript with the video automatically. You type up a transcript, upload it to YouTube, and YouTube processes the video and transcript together, using voice recognition to synchronize the transcript with the video. This feature tends to be entirely accurate. In some cases, no additional editing is necessary. In other cases, you need to tweak the timing a bit, but at least you don't have to do all the work manually.
Why it Matters
If a video has no caption, deaf users have limited or no access to the information contained in it. Even if a captions track is available, ensure that it contains all meaningful information in the video, not just dialogue.
Deaf viewers can see everything in the video but are not able to hear any of it without captions. Without a caption track, deaf viewers do not have a way of knowing the dialog, narration, or the essential sounds not spoken by people, such as "dramatic instrumental music," applause, screams, or other sounds that set the scene, provide context, or give meaning to the video.
Rule Description
An HTML5 video element must include a track element
with kind="captions" set as a property. The captions
should convey all meaningful auditory information in the video including
dialogue, musical cues, sound effects, and other relevant information for deaf
users.
The Algorithm (in simple terms)
Ensures video elements have captions.
Resources
Refer to the complete list of axe 4.4 rules.
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