WordPress at a glance
filter is not described

oembed_default_width filter-hook . WP 4.4.0

Filters the maxwidth oEmbed parameter.

Usage

add_filter( 'oembed_default_width', 'filter_function_name_5895' );
function filter_function_name_5895( $maxwidth ){
	// filter...

	return $maxwidth;
}
$maxwidth(int)
Maximum allowed width.
Default: 600

Where the hook is called

WP_oEmbed_Controller::register_routes()
oembed_default_width
wp-includes/class-wp-oembed-controller.php 32
$maxwidth = apply_filters( 'oembed_default_width', 600 );

Where the hook is used (in WP core)

Does not used.