@admlaw your case would be because by default we search the post content for the URLs, not meta data fields.
However, you are able to change that with the filter located at the snippet below:
https://github.com/WebDevStudios/Automatic-Featured-Images-from-Videos/blob/master/automatic-featured-images-from-videos.php#L103-L113
You could use the filter and the passed in post ID variable to fetch your ACF field and return that instead of the default content string. Something like this:
function admlaw_get_acf_youtube( $original_content, $post_id ) {
// Fetch the field we store our URL in.
$acf_field = get_field( 'my_field_id', $post_id );
// Only return it if we have something and it's an actual string.
if ( ! empty( $acf_field ) && is_string( $acf_field ) ) {
return $acf_field;
}
// May as well just return the original content at this point.
return $original_content;
}
add_filter( 'wds_featured_images_from_video_filter_content', 'admlaw_get_acf_youtube', 10, 2 );
You’ll want to replace the “my_field_id” with your actual fields.