Add media image to posts that have a media url

media-image.php

<?php
// add this code to a plugin, it only needs to run once so remove it when you're done
add_action('admin_init', function() {

	$the_query = new WP_Query( array( 'post_type' => 'post', 'posts_per_page' => 999 ) );
	// The Loop
	if ( $the_query->have_posts() ) {
		while ( $the_query->have_posts() ) {
			$the_query->the_post();

			// save meta field for the app
			if( get_post_meta( $the_query->post->ID, 'appp_media_url', 1 ) ) {

				// optionally add an image when the media is played
				$featured_url = wp_get_attachment_url( get_post_thumbnail_id( $the_query->post->ID ) );
				update_post_meta( $the_query->post->ID, 'appp_media_image', $featured_url );
			}
		}
		/* Restore original Post Data */
		wp_reset_postdata();
	} else {
		// no posts found
	}

});