  * build with configure flag --enable-avisynth
    when AviSynth+ is in Debian
    (embedded avisynth code dropped upstream)
  * build with configure flag --enable-libilbc
    when libilbc is in Debian
    closes: bug#675959
    <https://github.com/TimothyGu/libilbc>
  * build with configure flag --enable-libklvanc
    when libklvanc is in Debian
    <https://github.com/stoth68000/libklvanc>
  * build with configure flag --enable-libkvazaar
    when Kvazaar is in Debian
    <https://github.com/ultravideo/kvazaar>
  * build with configure flag --enable-libopenh264
    when OpenH264 is in Debian
    <https://github.com/cisco/openh264>
  * build with configure flag --enable-libtensorflow
    when Tensorflow is in Debian
    closes: bug#959765
  * build with configure flag --enable-libvmaf
    when VMAF is in Debian
    <https://github.com/Netflix/vmaf>
  * build with configure flag --enable-libxavs
    when XAVS is in Debian
    <http://xavs.sourceforge.net/>
  * build with configure flag --enable-vapoursynth
    when vapoursynth is in Debian
    closes: bug#833942
    <https://github.com/vapoursynth/vapoursynth>
  * build with configure flag --enable-libdavs2
    when davs2 is no longer deemed experimental
  * build with configure flag --enable-libxavs2
    when xavs2 is no longer deemed experimental
  * build with configure flag --enable-liblensfun
    when a released version of liblensfun is supported again
