{ stdenv, fetchurl, pkgconfig, yasm, bzip2, zlib, perl
, mp3Support    ? true,   lame      ? null
, speexSupport  ? true,   speex     ? null
, theoraSupport ? true,   libtheora ? null
, vorbisSupport ? true,   libvorbis ? null
, vpxSupport    ? true,   libvpx    ? null
, x264Support   ? false,  x264      ? null
, xvidSupport   ? true,   xvidcore  ? null
, faacSupport   ? false,  faac      ? null
, vaapiSupport  ? true,   libva     ? null
, vdpauSupport  ? true,   libvdpau  ? null
, freetypeSupport ? true, freetype  ? null # it's small and almost everywhere
, SDL # only for avplay in $bin, adds nontrivial closure to it
, enableGPL ? true # ToDo: some additional default stuff may need GPL
, enableUnfree ? faacSupport
, hostPlatform
}:

assert faacSupport -> enableUnfree;

let inherit (stdenv.lib) optional optionals hasPrefix; in

/* ToDo:
    - more deps, inspiration: http://packages.ubuntu.com/raring/libav-tools
    - maybe do some more splitting into outputs
*/

let
  result = {
    # e.g. https://libav.org/releases/libav-11.11.tar.xz.sha1
    libav_0_8 = libavFun "0.8.20" "0c7a2417c3a01eb74072691bb93ce802ae1be08f";
    libav_11  = libavFun "11.11"  "d7444fa4f135bdd7347cc962ab4b5228796b0f23";
    libav_12  = libavFun "12.2"   "3784b15f88076ca0ab8fb6b0377e975b83a5c9f5";
  };

  libavFun = version : sha1 : stdenv.mkDerivation rec {
    name = "libav-${version}";

    src = fetchurl {
      url = "${meta.homepage}/releases/${name}.tar.xz";
      inherit sha1; # upstream directly provides sha1 of releases over https
    };

    patches = []
      ++ optional (vpxSupport && hasPrefix "0.8." version) ./vpxenc-0.8.17-libvpx-1.5.patch
      ;

    preConfigure = "patchShebangs doc/texi2pod.pl";

    configureFlags =
      assert stdenv.lib.all (x: x!=null) buildInputs;
    [
      #"--enable-postproc" # it's now a separate package in upstream
      "--disable-avserver" # upstream says it's in a bad state
      "--enable-avplay"
      "--enable-shared"
      "--enable-runtime-cpudetect"
      "--cc=cc"
    ]
      ++ optionals enableGPL [ "--enable-gpl" "--enable-swscale" ]
      ++ optional mp3Support "--enable-libmp3lame"
      ++ optional speexSupport "--enable-libspeex"
      ++ optional theoraSupport "--enable-libtheora"
      ++ optional vorbisSupport "--enable-libvorbis"
      ++ optional vpxSupport "--enable-libvpx"
      ++ optional x264Support "--enable-libx264"
      ++ optional xvidSupport "--enable-libxvid"
      ++ optional faacSupport "--enable-libfaac --enable-nonfree"
      ++ optional vaapiSupport "--enable-vaapi"
      ++ optional vdpauSupport "--enable-vdpau"
      ++ optional freetypeSupport "--enable-libfreetype"
      ;

  nativeBuildInputs = [ pkgconfig ];
    buildInputs = [ lame yasm zlib bzip2 SDL ]
      ++ [ perl ] # for install-man target
      ++ optional mp3Support lame
      ++ optional speexSupport speex
      ++ optional theoraSupport libtheora
      ++ optional vorbisSupport libvorbis
      ++ optional vpxSupport libvpx
      ++ optional x264Support x264
      ++ optional xvidSupport xvidcore
      ++ optional faacSupport faac
      ++ optional vaapiSupport libva
      ++ optional vdpauSupport libvdpau
      ++ optional freetypeSupport freetype
      ;

    enableParallelBuilding = true;

    outputs = [ "bin" "dev" "out" ];
    setOutputFlags = false;

    # alltools to build smaller tools, incl. aviocat, ismindex, qt-faststart, etc.
    buildFlags = "all alltools install-man";

    postInstall = ''
      moveToOutput bin "$bin"
      # alltools target compiles an executable in tools/ for every C
      # source file in tools/, so move those to $out
      for tool in $(find tools -type f -executable); do
        mv "$tool" "$bin/bin/"
      done
    '';

    doInstallCheck = false; # fails randomly
    installCheckTarget = "check"; # tests need to be run *after* installation

    crossAttrs = {
      configurePlatforms = [];
      configureFlags = configureFlags ++ [
        "--cross-prefix=${stdenv.cc.prefix}"
        "--enable-cross-compile"
        "--target_os=linux"
        "--arch=${hostPlatform.arch}"
        ];
    };

    passthru = { inherit vdpauSupport; };

    meta = with stdenv.lib; {
      homepage = https://libav.org/;
      description = "A complete, cross-platform solution to record, convert and stream audio and video (fork of ffmpeg)";
      license = with licenses; if enableUnfree then unfree #ToDo: redistributable or not?
        else if enableGPL then gpl2Plus else lgpl21Plus;
      platforms = with platforms; linux ++ darwin;
      maintainers = [ maintainers.vcunat ];
    };
  }; # libavFun

in result