Source

File: wp-includes/media.php

function wp_plupload_default_settings() {
	$wp_scripts = wp_scripts();

	$data = $wp_scripts->get_data( 'wp-plupload', 'data' );
	if ( $data && false !== strpos( $data, '_wpPluploadSettings' ) ) {
		return;
	}

	$max_upload_size    = wp_max_upload_size();
	$allowed_extensions = array_keys( get_allowed_mime_types() );
	$extensions         = array();
	foreach ( $allowed_extensions as $extension ) {
		$extensions = array_merge( $extensions, explode( '|', $extension ) );
	}

	/*
	 * Since 4.9 the `runtimes` setting is hardcoded in our version of Plupload to `html5,html4`,
	 * and the `flash_swf_url` and `silverlight_xap_url` are not used.
	 */
	$defaults = array(
		'file_data_name' => 'async-upload', // Key passed to $_FILE.
		'url'            => admin_url( 'async-upload.php', 'relative' ),
		'filters'        => array(
			'max_file_size' => $max_upload_size . 'b',
			'mime_types'    => array( array( 'extensions' => implode( ',', $extensions ) ) ),
		),
	);

	/*
	 * Currently only iOS Safari supports multiple files uploading,
	 * but iOS 7.x has a bug that prevents uploading of videos when enabled.
	 * See #29602.
	 */
	if ( wp_is_mobile() && strpos( $_SERVER['HTTP_USER_AGENT'], 'OS 7_' ) !== false &&
		strpos( $_SERVER['HTTP_USER_AGENT'], 'like Mac OS X' ) !== false ) {

		$defaults['multi_selection'] = false;
	}

	/**
	 * Filters the Plupload default settings.
	 *
	 * @since 3.4.0
	 *
	 * @param array $defaults Default Plupload settings array.
	 */
	$defaults = apply_filters( 'plupload_default_settings', $defaults );

	$params = array(
		'action' => 'upload-attachment',
	);

	/**
	 * Filters the Plupload default parameters.
	 *
	 * @since 3.4.0
	 *
	 * @param array $params Default Plupload parameters array.
	 */
	$params = apply_filters( 'plupload_default_params', $params );

	$params['_wpnonce'] = wp_create_nonce( 'media-form' );

	$defaults['multipart_params'] = $params;

	$settings = array(
		'defaults'      => $defaults,
		'browser'       => array(
			'mobile'    => wp_is_mobile(),
			'supported' => _device_can_upload(),
		),
		'limitExceeded' => is_multisite() && ! is_upload_space_available(),
	);

	$script = 'var _wpPluploadSettings = ' . wp_json_encode( $settings ) . ';';

	if ( $data ) {
		$script = "$data\n$script";
	}

	$wp_scripts->add_data( 'wp-plupload', 'data', $script );
}