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

Media Data Atom TypesSubtitle MediaThe data format field in the sample description is always set to 'c608'.Note Closed caption tracks with data formats other than 'c608' are not defined by this specification.Unrecognized data formats should be ignored.Closed Captioning Sample DataThe format of the closed captioning sample data is a sequence of one or more atoms, one of which must bea 'cdat' atom. Unrecognized atoms should be ignored. For details about the content, refer to the specificationCEA-608-E, Line 21 Data Services, April, 2008 .SizeA 32-bit integer that specifies the number of bytes in this closed captioning media data atom.TypeA 32-bit integer that identifies the atom type; this field must be set to 'cdat'.Note Apple reserves all atom types with lowercase letters and numbers.Byte pair arrayAn array of one or more byte pairs for data channel 1/field 1 (“CC1”) of a CEA-608 data stream, each bytepair corresponding to a video frame.The durations of closed caption media samples can vary but should not be shorter than the number ofbyte pairs in the byte pair array. A closed caption media sample duration that is longer than the arraylength in video frames should treat additional durations as though null (0) byte pair bytes are received.Note The carriage of byte pairs for other elements of the source CEA-608-E frame data are not described here. Ifsupported, other atom types and their content will be documented.Subtitle MediaSubtitle media is used to store text data used for subtitles in QuickTime movies. It has a media type of 'sbtl'.Subtitles provide written versions of audio or visual content, such as to offer alternate language translationsor to supplement the content. Subtitles differ from closed captions in that subtitles are usually a translationof the sound track into a different language rather than a transcription of the sound track in the same language.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.199