Use plugin on pages

Should already work on pages/custom post types. The biggest question I’d end up having is if this theme uses the standard post editor content field, or if it’s setting up custom meta boxes for the place you’ve perhaps been testing with.

The plugin searches the post content field by default, but it can be filtered to search for a user-provided spot in replacement.

https://github.com/WebDevStudios/Automatic-Featured-Images-from-Videos/blob/master/automatic-featured-images-from-videos.php#L44-L49

Yes, I don’t see why it wouldn’t be possible. You’ll still need to use the filter highlighted above, but note that some spots in that link are updated recently and not matching what’s in the released version on WordPress.org here.

Chances are the video URL is being stored in post meta for the post(s) in question. Just a matter of figuring out which one. Once you know the meta_key for it, you’ll need to use the filter and return the meta_value for that custom field. By default the filter has a chunk of the post_content that it searches for URLs for. You’ll need to return an alternative value to the filter for the plugin to search through instead.

Admittedly, the filter, as is, won’t be great for initial views of the post editor, when there’s no post ID displayed in the URL. Once there is though, you should be able to grab that ID value via the $_GET global and use it to query for the custom field value inside your callback to the filter. I want to get this changed in a future release of the plugin.

Rough example code:

function filter_the_searched_content( $content ) {
    if ( ! empty( $_GET ) && isset( $_GET['post'] ) ) {
        // We have an ID. Let's check for a saved meta value.
        $meta = get_post_meta( 'my_meta_key', absint( $_GET['post'] ), true );
        if ( ! empty( $meta ) ) {
            // We have saved meta data! Let's return that to the filter so Auto Featured Images searches for a url there.
            return $meta;
        }
    }
    // We either didn't have an ID, or we didn't have meta content saved, so let's just return the original value.
    return $content;
}
add_filter( 'wds_featured_images_from_video_filter_content', 'filter_the_searched_content' );