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# Text box atom ('tbox')

An atom that defines a text box for a subtitle sample.

## Overview

This optional extension defines a text box for a subtitle sample, to be used as described in [`Sample extensions`](/documentation/quicktime-file-format/Subtitle_sample_data/Sample_extensions). If present, this overrides the default text box in the associated sample description. If the subtitle sample description’s Display flags do not include the Vertical Placement flag (`0x20000000`), the Text Box atom should not be included in any sample of the subtitle track.

## Topics

### Data fields

[`Size`](/documentation/quicktime-file-format/Text_box_atom/Size)

An unsigned 32-bit integer holding the size of the subtitle style atom.

[`Type`](/documentation/quicktime-file-format/Text_box_atom/Type)

An unsigned 32-bit field.

[`Text box`](/documentation/quicktime-file-format/Text_box_atom/Text_box)

A 64-bit rectangle that specifies an area to receive text (each 16 bits indicate top, left, bottom, and right, respectively) within the subtitle track.


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