WordPress at a glance
filter is not described

media_upload_form_url filter-hook . WP 2.6.0

Filters the media upload form action URL.

Usage

add_filter( 'media_upload_form_url', 'filter_function_name_9248', 10, 2 );
function filter_function_name_9248( $form_action_url, $type ){
	// filter...

	return $form_action_url;
}
$form_action_url(string)
The media upload form action URL.
$type(string)
The type of media.
Default: 'file'

Where the hook is called

media_upload_type_form()
wp-admin/includes/media.php 2011
$form_action_url = apply_filters( 'media_upload_form_url', $form_action_url, $type );
wp-admin/includes/media.php 2075
$form_action_url = apply_filters( 'media_upload_form_url', $form_action_url, $type );
wp-admin/includes/media.php 2218
$form_action_url = apply_filters( 'media_upload_form_url', $form_action_url, $type );
wp-admin/includes/media.php 2370
$form_action_url = apply_filters( 'media_upload_form_url', $form_action_url, $type );

Where the hook is used (in WP core)

Does not used.