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

Media Data Atom TypesText MediaText sampleextension'ftab''hlit''hclr''drpo''drpt''imag''metr'DescriptionTable of font names. Each table entry contains a font number (stored in a 16-bitinteger) and a font name (stored in a Pascal string).This atom is required if the 'styl'atom is present.Highlight information. The atom data consists of two 32-bit integers. The first containsthe starting offset for the highlighted text, and the second has the ending offset. Ahighlight sample can be in a key frame or in a differenced frame. When it’s used ina differenced frame, the sample should contain a zero-length piece of text.Highlight color. This atom specifies the 48-bit RGB color to use for highlighting.Drop shadow offset. When the display flags indicate drop shadow style, this atomcan be used to override the default drop shadow placement. The data consists oftwo 16-bit integers. The first indicates the horizontal displacement of the drop shadow,in pixels; the second, the vertical displacement.Drop shadow transparency. The data is a 16-bit integer between 0 and 256 indicatingthe degree of transparency of the drop shadow. A value of 256 makes the dropshadow completely opaque.Image font data. This atom contains two more atoms. An 'idat' atom containscompressed image data to be used to draw the text when the required fonts are notavailable. An 'idsc' atom contains a video sample description describing the formatof the compressed image data.Image font highlighting. This atom contains metric information that governshighlighting when an 'imag' atom is used for drawing.Hypertext and Wired TextHypertext is used as an action that takes you to a Web URL; like a Web URL, it appears blue and underlined.Hypertext is stored in a text track sample atom stream as type 'htxt'. The same mechanism is used to storewired actions linked to text strings. A text string can be wired to act as a hypertext link when clicked or toperform any defined QuickTime wired action when clicked. For details on wired actions, see “Wired ActionGrammar” (page 225).The data stored is a QTAtomContainer. The root atom of hypertext in this container is a wired-text atom oftype 'wtxt'. This is the parent for all individual hypertext objects.For each hypertext item, the parent atom is of type 'htxt'. This is the atom container atom type. Two childrenof this atom that define the offset of the hypertext in the text stream are:2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.197