The Timeline tool does not seem to support the media listed.
The info page states “For each event, you may add images and texts. You may also include assets from Twitter, YouTube, Flickr, Vimeo, Google Maps and SoundCloud.” and the field for Media Assets states “URL to the media (Twitter, YouTube, Flickr, Vimeo, Wikipedia, Google Maps and SoundCloud are currently supported).”
So far only YouTube URLS work as suggested.
Image Credit: The Entire Strawberry Crop flickr photo by cogdogblog shared into the public domain using Creative Commons Public Domain Dedication (CC0)