The IETF has just ratified RFC 5334 “Ogg Media Types”, which I have co-authored.

The new Ogg MIME types are as follows:

• audio/ogg for all Ogg files that contain predominantly audio, such as Ogg Vorbis files (.ogg or .oga), Ogg Speex files (.spx) or Ogg FLAC files. The file extension recommended to be used is .oga, but .ogg will continue to be used for Ogg Vorbis I files for backwards compatibility.
• video/ogg for all Ogg files that contain predominantly video, such as Ogg Theora or Ogg Dirac files. The file extension recommended to be used is .ogv. Please stop using .ogg for Ogg Theora files, since that causes havoc for any application trying to determine which application to use for opening such a file.
• application/ogg used to be the MIME type recommended for any Ogg encapsulated file. This is obsoleted by the new RFC. Instead, application/ogg is a generic MIME type that can be used for Ogg files containing custom content tracks. This may e.g. be a Ogg file with 5 vorbis, 2 speex, 2 theora, 5 CMML, 2 Kate, and a custom image tracks. Such files have to use the Skeleton extension to Ogg to be able to describe the content of the file. The file extension recommended to be used is .ogx.

The RFC also specifies the possibility of using codec parameters to the MIME types to specify directly within the MIME type what codecs are contained inside the files. This may for example be “video/ogg; codecs=’dirac,speex,CMML'”.

More details on these decisions and on further considered MIME types are in the Xiph wiki.

Disclaimer: I had no influence on the funny number game that happened between the obsoleted rfc3534 and the new rfc5334. 🙂

Happy MIME-typing!!