Hello - Plugin not retrieving video thumbnails on my end. The following is a video-type post w/ a vimeo sample video: http://reasonandfolly.com/borooklyn-grange-featurette/
As you know, with WP video post, The "Video Embed Code" is placed in "Video Format" field of "Post Format" panel.
I have checked the plugin settings and checked "post" for post types. Not clear if I need to worry about "custom field."
Not this if this is helpful but here's the code I think pertains to custom field from format-video.php file:
<article class="article-archive format-video" id="post-<?php the_ID(); ?>" > <span class="post-video"> <?php echo get_post_meta($post->ID, 'single_format_video', true); ?> </span>