$ ffmpeg -h encoder=libfdk_aac
Encoder libfdk_aac [Fraunhofer FDK AAC]:
    General capabilities: delay small 
    Threading capabilities: none
    Supported sample rates: 96000 88200 64000 48000 44100 32000 24000 22050 16000 12000 11025 8000
    Supported sample formats: s16
    Supported channel layouts: mono stereo 3.0 4.0 5.0 5.1 7.1(wide) 7.1
libfdk_aac AVOptions:
  -afterburner       <int>        E...A...... Afterburner (improved quality) (from 0 to 1) (default 1)
  -eld_sbr           <int>        E...A...... Enable SBR for ELD (for SBR in other configurations, use the -profile parameter) (from 0 to 1) (default 0)
  -eld_v2            <int>        E...A...... Enable ELDv2 (LD-MPS extension for ELD stereo signals) (from 0 to 1) (default 0)
  -signaling         <int>        E...A...... SBR/PS signaling style (from -1 to 2) (default default)
     default         -1           E...A...... Choose signaling implicitly (explicit hierarchical by default, implicit if global header is disabled)
     implicit        0            E...A...... Implicit backwards compatible signaling
     explicit_sbr    1            E...A...... Explicit SBR, implicit PS signaling
     explicit_hierarchical 2            E...A...... Explicit hierarchical signaling
  -latm              <int>        E...A...... Output LATM/LOAS encapsulated data (from 0 to 1) (default 0)
  -header_period     <int>        E...A...... StreamMuxConfig and PCE repetition period (in frames) (from 0 to 65535) (default 0)
  -vbr               <int>        E...A...... VBR mode (1-5) (from 0 to 5) (default 0)```

$ ffmpeg -h encoder=libx264
Encoder libx264 [libx264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10]:
    General capabilities: dr1 delay threads 
    Threading capabilities: other
    Supported pixel formats: yuv420p yuvj420p yuv422p yuvj422p yuv444p yuvj444p nv12 nv16 nv21 yuv420p10le yuv422p10le yuv444p10le nv20le gray gray10le
libx264 AVOptions:
  -preset            <string>     E..V....... Set the encoding preset (cf. x264 --fullhelp) (default "medium")
  -tune              <string>     E..V....... Tune the encoding params (cf. x264 --fullhelp)
  -profile           <string>     E..V....... Set profile restrictions (cf. x264 --fullhelp) 
  -fastfirstpass     <boolean>    E..V....... Use fast settings when encoding first pass (default true)
  -level             <string>     E..V....... Specify level (as defined by Annex A)
  -passlogfile       <string>     E..V....... Filename for 2 pass stats
  -wpredp            <string>     E..V....... Weighted prediction for P-frames
  -a53cc             <boolean>    E..V....... Use A53 Closed Captions (if available) (default true)
  -x264opts          <string>     E..V....... x264 options
  -crf               <float>      E..V....... Select the quality for constant quality mode (from -1 to FLT_MAX) (default -1)
  -crf_max           <float>      E..V....... In CRF mode, prevents VBV from lowering quality beyond this point. (from -1 to FLT_MAX) (default -1)
  -qp                <int>        E..V....... Constant quantization parameter rate control method (from -1 to INT_MAX) (default -1)
  -aq-mode           <int>        E..V....... AQ method (from -1 to INT_MAX) (default -1)
     none            0            E..V.......
     variance        1            E..V....... Variance AQ (complexity mask)
     autovariance    2            E..V....... Auto-variance AQ
     autovariance-biased 3            E..V....... Auto-variance AQ with bias to dark scenes
  -aq-strength       <float>      E..V....... AQ strength. Reduces blocking and blurring in flat and textured areas. (from -1 to FLT_MAX) (default -1)
  -psy               <boolean>    E..V....... Use psychovisual optimizations. (default auto)
  -psy-rd            <string>     E..V....... Strength of psychovisual optimization, in <psy-rd>:<psy-trellis> format.
  -rc-lookahead      <int>        E..V....... Number of frames to look ahead for frametype and ratecontrol (from -1 to INT_MAX) (default -1)
  -weightb           <boolean>    E..V....... Weighted prediction for B-frames. (default auto)
  -weightp           <int>        E..V....... Weighted prediction analysis method. (from -1 to INT_MAX) (default -1)
     none            0            E..V.......
     simple          1            E..V.......
     smart           2            E..V.......
  -ssim              <boolean>    E..V....... Calculate and print SSIM stats. (default auto)
  -intra-refresh     <boolean>    E..V....... Use Periodic Intra Refresh instead of IDR frames. (default auto)
  -bluray-compat     <boolean>    E..V....... Bluray compatibility workarounds. (default auto)
  -b-bias            <int>        E..V....... Influences how often B-frames are used (from INT_MIN to INT_MAX) (default INT_MIN)
  -b-pyramid         <int>        E..V....... Keep some B-frames as references. (from -1 to INT_MAX) (default -1)
     none            0            E..V.......
     strict          1            E..V....... Strictly hierarchical pyramid
     normal          2            E..V....... Non-strict (not Blu-ray compatible)
  -mixed-refs        <boolean>    E..V....... One reference per partition, as opposed to one reference per macroblock (default auto)
  -8x8dct            <boolean>    E..V....... High profile 8x8 transform. (default auto)
  -fast-pskip        <boolean>    E..V....... (default auto)
  -aud               <boolean>    E..V....... Use access unit delimiters. (default auto)
  -mbtree            <boolean>    E..V....... Use macroblock tree ratecontrol. (default auto)
  -deblock           <string>     E..V....... Loop filter parameters, in <alpha:beta> form.
  -cplxblur          <float>      E..V....... Reduce fluctuations in QP (before curve compression) (from -1 to FLT_MAX) (default -1)
  -partitions        <string>     E..V....... A comma-separated list of partitions to consider. Possible values: p8x8, p4x4, b8x8, i8x8, i4x4, none, all
  -direct-pred       <int>        E..V....... Direct MV prediction mode (from -1 to INT_MAX) (default -1)
     none            0            E..V.......
     spatial         1            E..V.......
     temporal        2            E..V.......
     auto            3            E..V.......
  -slice-max-size    <int>        E..V....... Limit the size of each slice in bytes (from -1 to INT_MAX) (default -1)
  -stats             <string>     E..V....... Filename for 2 pass stats
  -nal-hrd           <int>        E..V....... Signal HRD information (requires vbv-bufsize; cbr not allowed in .mp4) (from -1 to INT_MAX) (default -1)
     none            0            E..V.......
     vbr             1            E..V.......
     cbr             2            E..V.......
  -avcintra-class    <int>        E..V....... AVC-Intra class 50/100/200/300/480 (from -1 to 480) (default -1)
  -me_method         <int>        E..V....... Set motion estimation method (from -1 to 4) (default -1)
     dia             0            E..V.......
     hex             1            E..V.......
     umh             2            E..V.......
     esa             3            E..V.......
     tesa            4            E..V.......
  -motion-est        <int>        E..V....... Set motion estimation method (from -1 to 4) (default -1)
     dia             0            E..V.......
     hex             1            E..V.......
     umh             2            E..V.......
     esa             3            E..V.......
     tesa            4            E..V.......
  -forced-idr        <boolean>    E..V....... If forcing keyframes, force them as IDR frames. (default false)
  -coder             <int>        E..V....... Coder type (from -1 to 1) (default default)
     default         -1           E..V.......
     cavlc           0            E..V.......
     cabac           1            E..V.......
     vlc             0            E..V.......
     ac              1            E..V.......
  -b_strategy        <int>        E..V....... Strategy to choose between I/P/B-frames (from -1 to 2) (default -1)
  -chromaoffset      <int>        E..V....... QP difference between chroma and luma (from INT_MIN to INT_MAX) (default 0)
  -sc_threshold      <int>        E..V....... Scene change threshold (from INT_MIN to INT_MAX) (default -1)
  -noise_reduction   <int>        E..V....... Noise reduction (from INT_MIN to INT_MAX) (default -1)
  -udu_sei           <boolean>    E..V....... Use user data unregistered SEI if available (default false)
  -x264-params       <dictionary> E..V....... Override the x264 configuration using a :-separated list of key=value parameters