Bug on Featured Video/Audio Meta Key (ignored)

Hello !

Really nice plugin, with a lot of options, it helped me a lot because the official AMP plugin is buggy when you want to custom it.

However, on video post type, the plugin just ignore “Featured Video/Audio Meta Key” label. I wanted to use “_video_url” instead of “_featured_embed_code” and I had to change manually the value here :

		$meta_key = better_amp_get_theme_mod( 'better-amp-featured-va-key' );

		if ( empty( $media_key ) ) {
			$meta_key = '_video_url';
		}

It’s in single.php ligne 32 so I assumed that better-amp-featured-va-key is all the time empty.

I’m just saying that to improve the plugin. Thank you so much !