Embedded media types.
youtube:
handle urls of the form: https://www.youtube.com/watch?v=-_Z5otWqhSw&feature=youtu.be
- the &feature stuff seems to break our embedding
handle urls of the form: https://youtu.be/-_Z5otWqhSw
- gets redirected to: https://www.youtube.com/watch?v=-_Z5otWqhSw&feature=youtu.be