---
title: "Pixel aspect ratio ('pasp')"
framework: quicktime-file-format
role: symbol
role_heading: Atom
path: quicktime-file-format/pixel_aspect_ratio
---

# Pixel aspect ratio ('pasp')

An extension that specifies the height-to-width ratio of pixels found in the video sample.

## Mentioned in

QuickTime File Format change log Video sample data

## Overview

Overview This is a required extension for MPEG-4 and uncompressed Y´CbCr video formats when non-square pixels are used. It is optional when square pixels are used. The units of measure for the hSpacing and vSpacing parameters are not specified, as only the ratio matters. The units of measure for height and width must be the same, however. The following table shows some common pixel aspect ratios.  |  |   |  |   |  |   |  |   |  |   |  |   |  |   |  |   |  |   |  |

## Topics

### Data fields

- [Size](quicktime-file-format/pixel_aspect_ratio/size.md)
- [Type](quicktime-file-format/pixel_aspect_ratio/type.md)
- [hSpacing](quicktime-file-format/pixel_aspect_ratio/hspacing.md)
- [vSpacing](quicktime-file-format/pixel_aspect_ratio/vspacing.md)

## See Also

### Extending video sample descriptions

- [MPEG-4 elementary stream descriptor atom ('esds')](quicktime-file-format/mpeg-4_elementary_stream_descriptor_atom.md)
- [AVC decoder configuration atom ('avcC')](quicktime-file-format/avc_decoder_configuration_atom.md)
- [Color parameter atom ('colr')](quicktime-file-format/color_parameter_atom.md)
- [Clean aperture ('clap')](quicktime-file-format/clean_aperture.md)