Tumblr Video thumbnails not working on direct uploads

I've been trying to fix a Tumblr theme that displays video thumbnails on the main page. For some reason video thumbnails work fine when the video is being linked in from elsewhere but not for direct uploads.

I am using this to get the thumbnails

{block:VideoThumbnail}
{VideoThumbnailURL}
{/block:VideoThumbnail}

For direct uploads nothing inside the block generates on the page and for uploads from places like Vimeo or YouTube it grabs the thumbnail correctly.

I can't imagine tumblr doesn't provide thumbnails for their own videos and I've been told that this feature of the theme used to work. Is there a setting somewhere?