---
title: Track aperture mode dimension atoms
framework: quicktime-file-format
role: collectionGroup
role_heading: API Collection
path: quicktime-file-format/track_aperture_mode_dimension_atoms
---

# Track aperture mode dimension atoms

Atoms that store information for each of the track aperture presentation modes.

## Overview

Overview A video track in a QuickTime Movie can signal clean aperture and pixel aspect ratio information through image description extensions. The clean aperture defines the part of the encoded pixels to be displayed. The pixel aspect ratio is the aspect ratio of the encoded pixels. Conceptually the encoded pixels are decompressed, stretched (or shrunk) based on the pixel aspect ratio, and extra pixels are cropped off according to the clean aperture. note: QuickTime tracks define simple dimensions for their content in the track header dimensions. In the absence of a track aperture mode dimensions atom, the dimensions in the track header are used for all modes. Considering this context, the dimensions recorded in the image description define the dimensions of the encoded pixels (encoded dimensions). What’s actually displayed is a result of applying the pixel aspect ratio and the clean aperture (display dimensions). Although the result of applying the clean aperture and the pixel aspect ratio is what is intended for final display, there are cases where it is useful to display all the pixels that exist in the content for various different purposes. Readers parsing QuickTime movies require information allowing these different display modes in order to provide this flexibility: The information for each of these presentation modes are represented in the optional track aperture mode dimensions atoms. note: Older applications built prior to QuickTime 7 will continue to use the dimension values stored in the track header.

## Topics

### Track aperture mode dimension atoms

- [Track aperture mode dimensions atom ('tapt')](quicktime-file-format/track_aperture_mode_dimensions_atom.md)
- [Track clean aperture dimensions atom ('clef')](quicktime-file-format/track_clean_aperture_dimensions_atom.md)
- [Track production aperture dimensions atom ('prof')](quicktime-file-format/track_production_aperture_dimensions_atom.md)
- [Track encoded pixels dimensions atom ('enof')](quicktime-file-format/track_encoded_pixels_dimensions_atom.md)

## See Also

### Describing tracks

- [Track atom ('trak')](quicktime-file-format/track_atom.md)
- [Track header atom ('tkhd')](quicktime-file-format/track_header_atom.md)
- [Track exclude from autoselection atom ('txas')](quicktime-file-format/track_exclude_from_autoselection_atom.md)
- [Clipping atom ('clip')](quicktime-file-format/clipping_atom.md)
- [Clipping region atom ('crgn')](quicktime-file-format/clipping_region_atom.md)
- [Track matte atom ('matt')](quicktime-file-format/track_matte_atom.md)
- [Compressed matte atom ('kmat')](quicktime-file-format/compressed_matte_atom.md)
- [Edit atom ('edts')](quicktime-file-format/edit_atom.md)
- [Edit list atom ('elst')](quicktime-file-format/edit_list_atom.md)
- [Playing with edit lists](quicktime-file-format/playing_with_edit_lists.md)
- [Track load settings atom ('load')](quicktime-file-format/track_load_settings_atom.md)
- [Track reference atoms](quicktime-file-format/track_reference_atoms.md)
- [Track input map atoms](quicktime-file-format/track_input_map_atoms.md)