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# Subtitle sample description

An atom that defines how to interpret subtitle media data.

## Overview

The subtitle sample description contains information that defines how to interpret subtitle media data. This sample description is based on the standard sample description header, as described in [`Sample description atom`](/documentation/quicktime-file-format/Sample_description_atom).

> Note: Only one sample description is permitted in a `'sbtl'` track.

The data format field in the sample description is currently always set to `'tx3g'`. Unrecognized data formats should be ignored. The text media described here is based on the text box defined in the 3GPP Timed Text specification but provides a different track type and media handler designed specifically for subtitles.

The subtitle media handler adds some of its own fields to the sample description.

## Topics

### Data fields

[`Display flags`](/documentation/quicktime-file-format/Subtitle_sample_description/Display_flags)

A 32-bit integer containing flags that describe how the subtitle text should be drawn.

[`Reserved`](/documentation/quicktime-file-format/Subtitle_sample_description/Reserved)

An 8-bit integer.

[`Reserved`](/documentation/quicktime-file-format/Subtitle_sample_description/Reserved2)

An 8-bit integer.

[`Reserved`](/documentation/quicktime-file-format/Subtitle_sample_description/Reserved3)

A 32-bit integer.

[`Default text box`](/documentation/quicktime-file-format/Subtitle_sample_description/Default_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.

[`Reserved`](/documentation/quicktime-file-format/Subtitle_sample_description/Reserved4)

A 32-bit value.

[`Font identifier`](/documentation/quicktime-file-format/Subtitle_sample_description/Font_identifier)

A 16-bit value that must be set to the same font identifier as in the font table.

[`Font face`](/documentation/quicktime-file-format/Subtitle_sample_description/Font_face)

An 8-bit integer that indicates the font’s style.

[`Font size`](/documentation/quicktime-file-format/Subtitle_sample_description/Font_size)

An 8-bit value for the font size, expressed in points.

[`Foreground color`](/documentation/quicktime-file-format/Subtitle_sample_description/Foreground_color)

A 32-bit RGBA color that specifies the text’s color, 8 bits each for red, green, blue, and alpha (transparency).

[`Font table`](/documentation/quicktime-file-format/Subtitle_sample_description/Font_table)

An atom that identifies the font to use to display the text.


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