attachment_fields_to_save │ filter-hook │ ACF 1.0

This filter is documented in wp-admin/includes/media.php

Usage

add_filter( 'attachment_fields_to_save', 'wp_kama_attachment_fields_to_save_filter', 10, 2 );

/**
 * Function for `attachment_fields_to_save` filter-hook.
 * 
 * @param array $post       An array of post data.
 * @param array $attachment An array of attachment metadata.
 *
 * @return array
 */
function wp_kama_attachment_fields_to_save_filter( $post, $attachment ){

	// filter...
	return $post;
}

$post(array)

An array of post data.

$attachment(array)

An array of attachment metadata.

Where the hook is called

$post = apply_filters( 'attachment_fields_to_save', $post, $changes );

Where the hook is used in Advanced Custom Fields PRO

add_filter( 'attachment_fields_to_save', array( $this, 'save_attachment' ), 10, 2 );