Speex is a 3rd party format. It's stored in a spx file which is contained in the ogg file. 3DGS supports ogg, but it's for Vorbis audio only. Speex is a separate thing designed for voice compression only. They have a 3rd one called Theora for video compression, and it's supposed to compete with MPEG4. All three formats are stored in a ogg file. 3DGS only supports Vorbis at the moment, and I'm request for both Speex and Theora; however Speex would be higher priority for now.