OGG is a wrapper format for audio and audiovisual recordings. It is developed by the Xiph open source project. It is the recommended format for audio and video on Wikimedia Commons, and also, Firefox supports it because it’s unrestricted by software patents. 

The FFmpeg tool can help you to convert almost any audio and video file from the command line. It is free to use, and is available for Windows, Linux and Mac operating systems. However, before depositing audiovisual material in the DANS Archive, please always contact DANS for discussion on the available formats/containers and possible migrations.

OGG is a DANS non-preferred audio format/container.