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  "title" : "Handler reference atom ('hdlr')"
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# Handler reference atom ('hdlr')

An atom that specifies the media handler component that is to be used to interpret the media’s data.

## Overview

The handler reference atom has an atom type value of `'hdlr'`.

Historically, the handler reference atom was also used for data references. However, this isn’t the case anymore.

The handler atom within a media atom declares the process by which the media data in the stream may be presented, and thus, the nature of the media in a stream. For example, a video handler would handle a video track.

The layout of a handler reference atom is as follows.

|Handler reference atom                                                                                    |Bytes   |
|----------------------------------------------------------------------------------------------------------|--------|
|``doc://com.apple.qtff/documentation/quicktime-file-format/Handler_reference_atom/Size``                  |4       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Handler_reference_atom/Type``                  |4       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Handler_reference_atom/Version``               |1       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Handler_reference_atom/Flags``                 |3       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Handler_reference_atom/Component_type``        |4       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Handler_reference_atom/Component_subtype``     |4       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Handler_reference_atom/Component_manufacturer``|4       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Handler_reference_atom/Component_flags``       |4       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Handler_reference_atom/Component_flags_mask``  |4       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Handler_reference_atom/Component_name``        |Variable|

## Topics

### Data fields

[`Size`](/documentation/quicktime-file-format/Handler_reference_atom/Size)

A 32-bit integer that specifies the number of bytes in this handler reference atom.

[`Type`](/documentation/quicktime-file-format/Handler_reference_atom/Type)

A 32-bit integer that identifies the atom type.

[`Version`](/documentation/quicktime-file-format/Handler_reference_atom/Version)

A 1-byte specification of the version of this handler information.

[`Flags`](/documentation/quicktime-file-format/Handler_reference_atom/Flags)

A 3-byte space for handler information flags.

[`Component type`](/documentation/quicktime-file-format/Handler_reference_atom/Component_type)

A four-character code that identifies the type of the handler.

[`Component subtype`](/documentation/quicktime-file-format/Handler_reference_atom/Component_subtype)

A four-character code that identifies the type of the media handler or data handler.

[`Component manufacturer`](/documentation/quicktime-file-format/Handler_reference_atom/Component_manufacturer)

Reserved.

[`Component flags`](/documentation/quicktime-file-format/Handler_reference_atom/Component_flags)

Reserved.

[`Component flags mask`](/documentation/quicktime-file-format/Handler_reference_atom/Component_flags_mask)

Reserved.

[`Component name`](/documentation/quicktime-file-format/Handler_reference_atom/Component_name)

A counted string that specifies the name of the component — that is, the media handler used when this media was created.


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