Media files include pictures, sounds, and other resources used by a UJML application which are not processed by the UJML compiler. See Images, Audio Elements. The file extension of media files varies depending on the resource type and on the file type the device requires for that resource type. If you are writing an application that will run on different devices, you may have to prepare the same media resource in several different file types. See Image Support, Audio Support. 

In addition to the built-in media types UJML also supports any resource type used by a UJML extension.

Images, Audio Elements, Image Support, Audio Support