Contents

Extended language tag atom ('elng')

An atom that represents media language information.

Mentioned in

Overview

The extended language tag atom represents media language information based on the RFC 4646 (Best Common Practices (BCP) #47) industry standard. It is an optional peer of the media header atom and follows the definition of the media header atom in a QuickTime movie. There is at most one extended language tag atom per media atom and, in turn, per track. The extended language tag atom has an atom type of 'elng'.

Until the introduction of this atom type, QuickTime had support for languages via codes based on either ISO 639 or the classic Macintosh language codes. These language codes are associated to a media (per track) in a QuickTime movie and are referred to as the media language. For more information, see Language code values.

To distinguish the extended language support from the old system, it is referred to as the extended language tag as opposed to language code. The major advantage of the extended language tag is that it includes additional information such as region, script, variation, and so on, as parts (or subtags). For instance, this additional information allows distinguishing content in French as spoken in Canada from content in French as spoken in France.

The layout of an extended language tag atom is as follows.

Extended language tag atom

Bytes

Size

4

Type

4

Version

1

Flags

3

Language_tag_string

Variable

Additional notes:

  • The extended language tag overrides the media language if they are not consistent.

  • The extended language tag atom is optional; if it is absent, use the media language.

  • No validation of the language tag string is performed. Applications parsing QuickTime movies need to be prepared for an invalid language tag, and are expected to behave as if no information is found.

  • For best compatibility with earlier players, if an extended language tag is specified, specify the most compatible language code in the language field of the 'mdhd' atom (for example, “eng” if the extended language tag is “en-AU”). If there is no reasonably compatible tag, the packed form of 'und' can be specified in the language code of the 'mdhd' atom.

Topics

Data fields

See Also

Describing media