exclude-poster-images.php

<?php
/**
 * Media Grid:
 * Filter out any videopress video posters that we've downloaded,
 * so that they don't seem to display twice.
 */
add_filter( 'ajax_query_attachments_args', 'videopress_ajax_query_attachments_args' );
function videopress_ajax_query_attachments_args( $args ) {
	$meta_query = array(
		array(
			'key'     => 'videopress_poster_image',
			'compare' => 'NOT EXISTS',
		),
	);

	// If there was already a meta query, let's AND it via
	// nesting it with our new one. No need to specify the
	// relation, as it defaults to AND.
	if ( ! empty( $args['meta_query'] ) ) {
		$meta_query[] = $args['meta_query'];
	}
	$args['meta_query'] = $meta_query;

	return $args;
}

/**
 * Media List:
 * Do the same as ^^ but for the list view.
 */
add_action( 'pre_get_posts', 'videopress_media_list_table_query' );
function videopress_media_list_table_query( $query ) {
	if ( is_admin() && $query->is_main_query() && ( 'upload' === get_current_screen()->id ) ) {
		$meta_query = array(
			array(
				'key'     => 'videopress_poster_image',
				'compare' => 'NOT EXISTS',
			),
		);

		if ( $old_meta_query = $query->get( 'meta_query' ) ) {
			$meta_query[] = $old_meta_query;
		}

		$query->set( 'meta_query', $meta_query );
	}
}