Encoder libspeex [libspeex Speex]:
    Supported sample rates: 8000 16000 32000
    Supported sample formats: s16
    Supported channel layouts: mono stereo
libspeex AVOptions:
-abr               <int>        E...A. Use average bit rate (from 0 to 1)
-cbr_quality       <int>        E...A. Set quality value (0 to 10) for CBR (from 0 to 10)
-frames_per_packet <int>        E...A. Number of frames to encode in each packet (from 1 to 8)
-vad               <int>        E...A. Voice Activity Detection (from 0 to 1)
-dtx               <int>        E...A. Discontinuous Transmission (from 0 to 1)

