Third-party apps on a mobile device can expose their content, such as audio content, video content, music stations, audio books, and so forth, to an in-vehicle computing device via a standardized format for content items that is decoupled from the user interfaces of the third-party apps. In this way, the in-vehicle computing device can display the content items in an in-vehicle user interface without granting providers of the content items access to the in-vehicle user interface. This system can present the content items in a different, independent user interface, even though the content items are associated with a third-party app having its own user interface. Content items encapsulate metadata describing the media, such as a title, subtitle, artwork, playback progress, a content item type, whether the content item is playable, whether the content item is a container item, and so forth.