Convert caf to spx

What is the difference between .caf and .spx?

Description: Digital audio format based on Apple's Core Audio technology; stores audio data as well as text annotations, markers, channel layouts, and other information; similar to an .AIFF or .WAVE file, but does not have a 4GB size limit and can store any number of audio channels.; 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.