WordPress at a glance
filter is not described

wp_generate_attachment_metadata filter-hook . WP 2.1.0

Filters the generated attachment meta data.

Usage

add_filter( 'wp_generate_attachment_metadata', 'filter_function_name_398', 10, 2 );
function filter_function_name_398( $metadata, $attachment_id ){
	// filter...

	return $metadata;
}
$metadata(array)
An array of attachment meta data.
$attachment_id(int)
Current attachment ID.

Where the hook is called

wp_generate_attachment_metadata()
wp-admin/includes/image.php 293
return apply_filters( 'wp_generate_attachment_metadata', $metadata, $attachment_id );

Where the hook is used (in WP core)

Does not used.