Convert ogv to spx

What is the difference between .ogv and .spx?

Description: Video file that uses the Xiph.Org's open source Ogg container format; may contain video streams that use one or more different codecs, such as Theora; can be played using a variety of media players.; Audio file compressed using Speex compression and saved in the Ogg Vorbis container format; designed as an audio compression format specifically for speech; compresses voice at 2 to 44 kbps and supports 8 kHz, 16 kHz, and 32 kHz compression in the same bitstream.