oEmbed is another form of previewing a URL which requires talking to a provider. By default the media repo has oEmbed previews disabled for privacy concerns, however this can be changed with the following configuration:
urlPreviews: oEmbed: true
The media repo ships with oEmbed's official providers list
bundled in and will use that if an alternative
providers.json is not specified. The
providers.json is considered an "asset" for the media repo, and can be changed by specifying an
asset path as a command line flag.