---
title: Atom index
framework: QuickTime File Format
role: symbol
role_heading: Data field
path: quicktime-file-format/preview_atom/atom_index
---

# Atom index

A 16-bit integer that identifies which atom of the specified type is to be used as the preview.

## Overview

Overview Typically, this field is set to 1 to indicate that you should use the first atom of the type specified in the atom type field.

## See Also

### Atom fields

- [Size](quicktime-file-format/preview_atom/size.md)
- [Type](quicktime-file-format/preview_atom/type.md)
- [Modification date](quicktime-file-format/preview_atom/modification_date.md)
- [Version number](quicktime-file-format/preview_atom/version_number.md)
- [Atom type](quicktime-file-format/preview_atom/atom_type.md)