ffmpeg -h decoder=libspeex
ffmpeg version 3.3 Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.4) 20160609
  configuration: --enable-gpl --enable-libass --enable-libfreetype --enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-nonfree --enable-gnutls --enable-ladspa --enable-libxavs --enable-libpulse --enable-librubberband --enable-libshine --enable-libflite --enable-libspeex --enable-libvo-amrwbenc --enable-libsnappy --enable-libwebp --enable-version3 --enable-encoder=libx262
  libavutil      55. 58.100 / 55. 58.100
  libavcodec     57. 89.100 / 57. 89.100
  libavformat    57. 71.100 / 57. 71.100
  libavdevice    57.  6.100 / 57.  6.100
  libavfilter     6. 82.100 /  6. 82.100
  libswscale      4.  6.100 /  4.  6.100
  libswresample   2.  7.100 /  2.  7.100
  libpostproc    54.  5.100 / 54.  5.100
Decoder libspeex [libspeex Speex]:
    General capabilities: dr1 delay subframes 
    Threading capabilities: none





ffmpeg -h encoder=libspeex
ffmpeg version 3.3 Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.4) 20160609
  configuration: --enable-gpl --enable-libass --enable-libfreetype --enable-libmp3lame --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-nonfree --enable-gnutls --enable-ladspa --enable-libxavs --enable-libpulse --enable-librubberband --enable-libshine --enable-libflite --enable-libspeex --enable-libvo-amrwbenc --enable-libsnappy --enable-libwebp --enable-version3 --enable-encoder=libx262
  libavutil      55. 58.100 / 55. 58.100
  libavcodec     57. 89.100 / 57. 89.100
  libavformat    57. 71.100 / 57. 71.100
  libavdevice    57.  6.100 / 57.  6.100
  libavfilter     6. 82.100 /  6. 82.100
  libswscale      4.  6.100 /  4.  6.100
  libswresample   2.  7.100 /  2.  7.100
  libpostproc    54.  5.100 / 54.  5.100
Encoder libspeex [libspeex Speex]:
    General capabilities: delay 
    Threading capabilities: none
    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) (default 0)
  -cbr_quality       <int>        E...A... Set quality value (0 to 10) for CBR (from 0 to 10) (default 8)
  -frames_per_packet <int>        E...A... Number of frames to encode in each packet (from 1 to 8) (default 1)
  -vad               <int>        E...A... Voice Activity Detection (from 0 to 1) (default 0)
  -dtx               <int>        E...A... Discontinuous Transmission (from 0 to 1) (default 0)