Index: embed-content.php
===================================================================
--- embed-content.php	(revision 40416)
+++ embed-content.php	(working copy)
@@ -21,7 +21,10 @@
 		if ( 'attachment' === get_post_type() && wp_attachment_is_image() ) {
 			$thumbnail_id = get_the_ID();
 		}
-
+        /**
+         * Added filter for the embed_thumbnail_id
+         */
+        $thumbnail_id = apply_filters( 'embed_thumbnail_id', $thumbnail_id );
 		if ( $thumbnail_id ) {
 			$aspect_ratio = 1;
 			$measurements = array( 1, 1 );