---
title: "Sample description atom ('stsd')"
framework: quicktime-file-format
role: symbol
role_heading: Atom
path: quicktime-file-format/sample_description_atom
---

# Sample description atom ('stsd')

An atom that stores information that allows you to decode samples in the media.

## Mentioned in

MPEG-1 media Music media QuickTime File Format change log Sprite media

## Overview

Overview The data stored in the sample description varies, depending on the media type. For example, in the case of video media, the sample descriptions are image description structures. The sample description information for each media type is explained in Media data atom types. The layout of the sample description atom is as follows.  |   |   |   |   |   |   |  The sample description atom has an atom type of 'stsd'. The sample description atom contains a table of sample descriptions. A media may have one or more sample descriptions, depending upon the number of different encoding schemes used in the media and on the number of files used to store the data. The sample-to-chunk atom identifies the sample description for each sample in the media by specifying the index into this table for the appropriate description (see Sample-to-chunk atom ('stsc')). General structure of a sample description While the exact format of the sample description varies by media type, the first four fields of every sample description are the same. important: When parsing sample descriptions in the ‘stsd’ atom, be aware of the sample description size value in order to read each table entry correctly. Some sample descriptions terminate with four zero bytes that are not otherwise indicated. These four fields may be followed by additional data specific to the media type and data format. See Media data atom types for additional details regarding specific media types and media formats.

## Topics

### Data fields

- [Size](quicktime-file-format/sample_description_atom/size.md)
- [Type](quicktime-file-format/sample_description_atom/type.md)
- [Version](quicktime-file-format/sample_description_atom/version.md)
- [Flags](quicktime-file-format/sample_description_atom/flags.md)
- [Number of entries](quicktime-file-format/sample_description_atom/number_of_entries.md)
- [Sample description table](quicktime-file-format/sample_description_atom/sample_description_table.md)

## See Also

### Describing samples

- [Sample table atom ('stbl')](quicktime-file-format/sample_table_atom.md)
- [Seeking with a QuickTime file](quicktime-file-format/seeking_with_a_quicktime_file.md)
- [Time-to-sample atom ('stts')](quicktime-file-format/time-to-sample_atom.md)
- [Creating video tracks at 30 frames per second](quicktime-file-format/creating_video_tracks_at_30_frames_per_second.md)
- [Creating video tracks at 29.97 frames per second](quicktime-file-format/creating_video_tracks_at_2997_frames_per_second.md)
- [Creating sound tracks at 44.1 kHz](quicktime-file-format/creating_sound_tracks_at_441_khz.md)
- [Composition offset atom ('ctts')](quicktime-file-format/composition_offset_atom.md)
- [Composition shift least greatest atom ('cslg')](quicktime-file-format/composition_shift_least_greatest_atom.md)
- [Using composition offset and composition shift least greatest atoms](quicktime-file-format/using_composition_offset_and_composition_shift_least_greatest_atoms.md)
- [Sync sample atom ('stss')](quicktime-file-format/sync_sample_atom.md)
- [Partial sync sample atom ('stps')](quicktime-file-format/partial_sync_sample_atom.md)
- [Sample-to-chunk atom ('stsc')](quicktime-file-format/sample-to-chunk_atom.md)
- [Referencing two data files with a single track](quicktime-file-format/referencing_two_data_files_with_a_single_track.md)
- [Sample size atom ('stsz')](quicktime-file-format/sample_size_atom.md)
- [Chunk offset atom ('stco')](quicktime-file-format/chunk_offset_atom.md)