wp-custom-url-rewrite.php

<?php

/* ------------------------------------------------------
 * | REWRITE URL FOR PODCASTS
 * ------------------------------------------------------
 *
 * The Url would be, siteurl.com/podcasts/podcast-slug
 *
 * ------------------------------------------------------ */

// Add a Rewrite Tag
function custom_rewrite_tag() {
    add_rewrite_tag('%podcasts%', '([^&]+)');
}
add_action('init', 'custom_rewrite_tag', 10, 0);

// Add a Rewrite Rule
function custom_rewrite_rule() {
    add_rewrite_rule('^podcasts/([^/]*)/?','index.php?page_id={your-page-id}&podcasts=$matches[1]','top');
}
add_action('init', 'custom_rewrite_rule', 10, 0);