WordPress soft crop function using intermediate_image_sizes_advanced()

gistfile1.txt

function soft_crop( $sizes ) {
    $sizes['medium'] = array(
        'width'  => 300,
        'height' => 0,
        'crop'   => true, 
    );
    return $sizes;
}
add_filter( 'intermediate_image_sizes_advanced', 'soft_crop' );