Quicktime File Format (2012-08-14).pdf

Movie AtomsMedia AtomsTime scaleA time value that indicates the time scale for this media—that is, the number of time units that pass persecond in its time coordinate system.DurationThe duration of this media in units of its time scale.LanguageA 16-bit integer that specifies the language code for this media. See “Language Code Values” (page 316)for valid language codes. Also see “Extended Language Tag Atom” (page 82) for the preferred code touse here if an extended language tag is also included in the media atom.QualityA 16-bit integer that specifies the media’s playback quality—that is, its suitability for playback in a givenenvironment.Extended Language Tag AtomThe extended language tag atom represents media language information based on the RFC 4646 (Best CommonPractices (BCP) #47) industry standard. It is an optional peer of the media header atom and should follow thedefinition of the media header atom in a QuickTime movie. There is at most one extended language tag atomper 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 ISO639 or the classic “Macintosh Language Codes” (page 317). These language codes are associated to a media(per track) in a QuickTime movie and are referred to as the media language.To distinguish the extended language support from the old system, it is referred to as the extended languagetag as opposed to language code . The major advantage of the extended language tag is that it includesadditional information such as region, script, variation, and so on, as parts (or subtags). For instance, thisadditional information allows distinguishing content in French as spoken in Canada from content in Frenchas spoken in France.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.82