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

Some Useful Examples and ScenariosPreparing Sound and Subtitle Alternate Groups for Use with Apple DevicesAlternate Subtitle TracksFor an alternate group that contains multiple subtitle ('sbtl') tracks:●●The player must pick a subtitle track even when subtitle display is turned off.If any of the requirements stated in “General” (page 334) does not hold, players may act as though thereis no alternate subtitle track information.As described in “Subtitle Sample Data” (page 202), a subtitle track can contain any combination of forced (mustbe displayed) and non-forced (optionally displayed) subtitle samples, including the possibility of a track thatcontains only forced subtitle samples. Even if a user indicates, directly or indirectly, that no subtitles shouldbe displayed, any available appropriate subtitle track should be enabled so that any forced subtitles in thetrack can be displayed. A means by which a player can make a default selection among subtitle alternates inthe absence of a user selection is covered in “Relationships Across Alternate Groups” (page 336).For each language in a subtitle alternate group, subtitle tracks can be configured in either of the followingways:●●Single track: Contains any combination of forced and non-forced (regular) subtitle samples.Track pairs: One track contains any combination of forced and non-forced (regular) subtitle samples andhas a track reference of type 'forc' that references the second track, which contains only forced samples,as described in “Subtitle Sample Data” (page 202).If the user or player picks the language of a track pair, the player application then selects the appropriate trackof the pair. It must select the regular subtitle track if subtitle display is on or the forced-only subtitle track ifsubtitle display is off.If a track pair is present in a subtitle alternate group, a player that displays the track languages of subtitle tracksmay choose to list the language only once. If a player lists both tracks of the pair, the player should displaysome kind of distinction between the tracks (for example, including the track names from the 'tnam' userdata in a menu).Alternate Sound TracksFor an alternate group that contains multiple sound ('soun') tracks:●●●If more than one alternate group contains sound tracks, the alternate group that contains the enabledsound track should be considered to be the primary alternate sound track group. Other alternate groupscontaining sound tracks should be ignored.If there is more than one enabled sound track, or if there is an enabled sound track and a non-sound trackinside the same alternate group, the player may act as though there is no alternate sound track information.Players may ignore sound tracks that use codecs that are unavailable.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.335