HTML - <track>

The HTML <track> element is used as a child of the media elements—<audio> and <video>. It lets you specify timed text tracks (or time-based data), for example to automatically handle subtitles. The tracks are formatted in WebVTT format (.vtt files) — Web Video Text Tracks.

Example

<video controls poster="/images/sample.gif">
   <source src="sample.mp4" type="video/mp4">
   <source src="sample.ogv" type="video/ogv">
   <track kind="captions" src="sampleCaptions.vtt" srclang="en">
   <track kind="descriptions" src="sampleDescriptions.vtt" srclang="en">
   <track kind="chapters" src="sampleChapters.vtt" srclang="en">
   <track kind="subtitles" src="sampleSubtitles_de.vtt" srclang="de">
   <track kind="subtitles" src="sampleSubtitles_en.vtt" srclang="en">
   <track kind="subtitles" src="sampleSubtitles_ja.vtt" srclang="ja">
   <track kind="subtitles" src="sampleSubtitles_oz.vtt" srclang="oz">
   <track kind="metadata" src="keyStage1.vtt" srclang="en" label="Key Stage 1">
   <track kind="metadata" src="keyStage2.vtt" srclang="en" label="Key Stage 2">
   <track kind="metadata" src="keyStage3.vtt" srclang="en" label="Key Stage 3">
   <!-- Fallback -->
   ...
</video>

Description  

The HTML <track> element is used as a child of the media elements—<audio> and <video>. It lets you specify timed text tracks (or time-based data), for example to automatically handle subtitles. The tracks are formatted in WebVTT format (.vtt files) — Web Video Text Tracks.

The type of data that track adds to the media is set in the kind attribute, which can take values of subtitles, captions, descriptions, chapters or metadata. The element points to a source file containing timed text that the browser exposes when the user requests additional data.

A media element cannot have more than one track with the same kind, srclang, and label.

Content categories None
Permitted content None, it is an empty element.
Tag omission As it is a void element, the start tag must be present and the end tag must not be present.
Permitted parent elements A media element, before any flow content.
Normative document HTML5, section 4.8.9

Attributes

Includes the Global Attributes.

NameVersionDescription
default This attribute indicates that the track should be enabled unless the user's preferences indicate that another track is more appropriate. This may only be used on one track element per media element.
kind How the text track is meant to be used. If omitted the default kind is subtitles. If the attribute is not present, it will use the subtitles. If the attribute contains an invalid value, it will use metadata. (Versions of Chrome earlier than 52 treated an invalid value as subtitles.) The following keywords are allowed:
  • subtitles
    • Subtitles provide translation of content that cannot be understood by the viewer. For example dialogue or text that is not English in an English language film.
    • Subtitles may contain additional content, usually extra background information. For example the text at the beginning of the Star Wars films, or the date, time, and location of a scene.
  • captions
    • Closed captions provide a transcription and possibly a translation of audio.
    • It may include important non-verbal information such as music cues or sound effects. It may indicate the cue's source (e.g. music, text, character).
    • Suitable for users who are deaf or when the sound is muted.
  • descriptions
    • Textual description of the video content.
    • Suitable for users who are blind or where the video cannot be seen.
  • chapters
    • Chapter titles are intended to be used when the user is navigating the media resource.
  • metadata
    • Tracks used by scripts. Not visible to the user.
label A user-readable title of the text track which is used by the browser when listing available text tracks.
src Address of the track (.vtt file). Must be a valid URL. This attribute must be defined.
srclang Language of the track text data. It must be a valid BCP 47 language tag. If the kind attribute is set to subtitles, then srclang must be defined.

Browser Compatibility  

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 23 24 (24)[2] 10 12.10 6
src attribute settable ? 50 (50)[3] ? ? ?
Invalid kind value as metadata No support No support No support No support No support
Feature Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support 25[1] 24.0 (24)[2] No support No support No support
src attribute settable ? 50.0 (50)[3] No support No support No support
Invalid kind value as metadata No support No support No support No support No support

[1] In Chrome for Android, the <track> element doesn’t work for fullscreen video yet.

[2] The <track> element, the HTMLTrackElement interface, and associated APIs were implemented in Firefox 24 behind the preference media.webvtt.enabled, which is disabled by default. To enable WebVTT support, set this preference to true. WebVTT is enabled by default starting in Firefox 31 and can be disabled by setting the preference to false.

[3] Until Firefox 50, the src attribute is settable, but the change does not get handled properly. Starting in Firefox 50, existing track data is properly disposed of, new track data is loaded and put into effect, and so forth.

See Also  

Specifications  

Specification Status Comment
HTML5
The definition of '<track>' in that specification.		 Recommendation Initial definition

DOM interface

This element implements the HTMLTrackElement interface.

License

© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/html/element/track