Add muted and playsinline attributes to WordPress generated video tag to force autoplay on mobile.

21477-add-muted-playsinline-for-video-autoplay-on-mobile.php

<?php // Ignore this line when adding to your child theme functions.php file.

/** || Add muted and playsinline to force autoplay on mobile. */
add_filter( 'wp_video_shortcode', function( $html ) {
   return str_replace( '<video', '<video muted playsinline ', $html );
} );