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

Media Data Atom TypesSubtitle MediaDefault text boxA 64-bit rectangle that specifies an area to receive text (each 16 bits indicate top, left, bottom, and right,respectively) within the subtitle track. This rectangle must fill the track header dimensions exactly; thatis, top is 0, left is 0, bottom is the height of the subtitle track header, and right is the width of the subtitletrack header. See “Subtitle Track Header Size and Placement” (page 205).ReservedA 32-bit value that must be set to 0.Font identifierA 16-bit value that must be set to the same font identifier as in the font table ('ftab' extension).Font faceAn 8-bit integer that indicates the font’s style. Set this field to 0 for normal text. You can enable otherstyle options by using one or more of the bit masks listed in Table 4-11 (page 201).Table 4-11Value0x00010x00020x0004Font face valuesMeaningBoldItalicUnderlineFont sizeAn 8-bit value that should always be 0.05 multiplied by the video track header height. For example, ifthe video track header is 720 points in height, this should be 36 (points). This size should be used in thedefault style record and in any per-sample style records. If a subtitle does not fit in the text box, thesubtitle media handler may choose to shrink the font size so that the subtitle fits.Foreground colorA 32-bit RGBA color that specifies the text’s color, 8 bits each for red, green, blue, and alpha (transparency).For example, this would be (0,0,0,255) for opaque black or (255,255,255,255) for opaque white. Darkcolors are not recommended, as the text could be placed onto a dark background.Font tableAn atom of type 'ftab' that identifies the font to use to display the text. See “Font Table Atom” (page201).Font Table AtomThis atom specifies the font used to display the subtitle.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.201