Nedtes

My ideas, thoughts and questions, but mostly just software

Learning Nix by Example: Building FFmpeg 4.0

What’s NIX ?

Nix is a functional package manager that guarantees reproducible independent and isolated builds for each package. It’s portable across operating systems. Long story short, it’s a greate package for your next software project. It was designed as part of a PhD thesis and it grew from there to be the system it is today.

However there are a few issues that a lot of people have complained about. The top issue I have seen is the learning curve for it. So we will be going through an example step by step now. Compiling the FFmpeg 4.0 is something I have chosen since it contains all the basic concepts to compile a nix package and should be good to give you a good idea how to compile other packages on your own.

Compiling FFmpeg 4.0

Let’s get started by creating our nix expressions.

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mkdir nix_packages && cd nix_packages
touch ffmpeg.nix default.nix

We will be working on these files as we progress.

Importing the source files

Nix imports the sources for your package by itself, you can have them in a compressed file. A git repository, or a git repo on Github.

ffmpeg.nix
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{ stdenv, fetchurl}:

stdenv.mkDerivation rec {
  name = "ffmpeg-${version}";
  version = "4.0";
  src = fetchurl {
    url = "https://github.com/FFmpeg/FFmpeg/archive/ace829cb45cff530b8a0aed6adf18f329d7a98f6.tar.gz";
    sha256 = "1v3ji6r2mvr4h1f9c4ml95h7zpm3hna8zh73m7769na8gvakfhcg";
  };
}

You can see stdenv and fetchurl at the top. This is the way nix declares its dependencies, stdenv and fetchurl are derivations in nix world. And we will need to use them, you can see that we use stdenv.mkDerivation to create the current ffmpeg derivation. We use fetchurl to fetch the sources from Github. We are choosing to pull a compressed archive.

One question you might have now, is that how can you know the sha256 beforehead. Nix got you covered, there’s a utility that comes with nix called nix-prefetch-url. It will fetch the file and give you the hash for it.

Now, let’s say you don’t want to fetch the archive and want to fetch the git repo.

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{ stdenv, fetchgit}:

stdenv.mkDerivation rec {
  name = "ffmpeg-${version}";
  version = "4.0";
  src = fetchgit {
    url = "https://git.ffmpeg.org/ffmpeg.git";
    rev = "ace829cb45cff530b8a0aed6adf18f329d7a98f6";
    sha256 = "1055za9dndx9rjq1zhs8ll8v3d8zf7m23frl8q11d7caki7s7yw3";
  };
}

To know the hash for this, there’s a nix utility also, but you have to install it this time. nix-env -i nix-prefetch-git and nix-prefetch-git --rev ace829cb45cff530b8a0aed6adf18f329d7a98f6 https://git.ffmpeg.org/ffmpeg.git

Adding other ffmpeg dependencies

In order to compile ffmpeg we will of course need a lot of other libraries that ffmpeg depends on. And choose to enable or disable ffmpeg own libraries. We set which ffmpeg internal libraries to build next.

ffmpeg.nix
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{ stdenv
, fetchgit
/* FFmpeg libraries to build, boolean values */
, avcodecLibrary ? true # Build avcodec library
, avdeviceLibrary ? true # Build avdevice library
, avfilterLibrary ? true # Build avfilter library
, avformatLibrary ? true # Build avformat library
, avresampleLibrary ? true # Build avresample library
, avutilLibrary ? true # Build avutil library
, postprocLibrary ? true # Build postproc library
, swresampleLibrary ? true # Build swresample library
, swscaleLibrary ? true # Build swscale library}:


let
  inherit (stdenv.lib) enableFeature;
in

stdenv.mkDerivation rec {
  name = "ffmpeg-${version}";
  version = "4.0";
  src = fetchgit {
    url = "https://git.ffmpeg.org/ffmpeg.git";
    rev = "ace829cb45cff530b8a0aed6adf18f329d7a98f6";
    sha256 = "1055za9dndx9rjq1zhs8ll8v3d8zf7m23frl8q11d7caki7s7yw3";
  };

  configureFlags = [
    (enableFeature avcodecLibrary "avcodec")
    (enableFeature avdeviceLibrary "avdevice")
    (enableFeature avfilterLibrary "avfilter")
    (enableFeature avformatLibrary "avformat")
    (enableFeature avresampleLibrary "avresample")
    (enableFeature avutilLibrary "avutil")
    (enableFeature (postprocLibrary && gplLicensing) "postproc")
    (enableFeature swresampleLibrary "swresample")
    (enableFeature swscaleLibrary "swscale")
  ];

}

You can notice we are using enableFeature, it’s just a simple function that takes a boolean value and library name and generates the configuration flag.

For the first case, it will take true (avcodecLibrary value) and avcodec and generate –enable-avcodec.

Now, we add some external dependencies, please note that all dependencies you mention need to have already existing nix expressions and you will be calling that nix expression name. To find if your requirement exists or not, you can check all-packages.nix

ffmpeg.nix
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{ stdenv
, fetchgit
/*
 * FFmpeg libraries to build
 */
, avcodecLibrary ? true # Build avcodec library
, avdeviceLibrary ? true # Build avdevice library
, avfilterLibrary ? true # Build avfilter library
, avformatLibrary ? true # Build avformat library
, avresampleLibrary ? true # Build avresample library
, avutilLibrary ? true # Build avutil library
, postprocLibrary ? true # Build postproc library
, swresampleLibrary ? true # Build swresample library
, swscaleLibrary ? true # Build swscale library
/*
 * External libraries (need to be matching nix expressions)
 */
, alsaLib ? null # Alsa in/output support
, avisynth ? null # Support for reading AviSynth scripts
, bzip2 ? null
, celt ? null # CELT decoder
, fdkaacExtlib ? false
, fdk_aac ? null # Fraunhofer FDK AAC de/encoder
, fontconfig ? null # Needed for drawtext filter
, freetype ? null # Needed for drawtext filter
, frei0r ? null # frei0r video filtering
, fribidi ? null # Needed for drawtext filter
, game-music-emu ? null # Game Music Emulator
, gnutls ? null
, gsm ? null # GSM de/encoder
, libjack2 ? null # Jack audio (only version 2 is supported in this build)
, ladspaH ? null # LADSPA audio filtering
, lame ? null # LAME MP3 encoder
, libass ? null # (Advanced) SubStation Alpha subtitle rendering
, libbluray ? null # BluRay reading
, libbs2b ? null # bs2b DSP library
, libcaca ? null # Textual display (ASCII art)
, libdc1394 ? null, libraw1394 ? null # IIDC-1394 grabbing (ieee 1394)
, libiconv ? null
, libmfx ? null # Hardware acceleration vis libmfx
, libmodplug ? null # ModPlug support
, libogg ? null # Ogg container used by vorbis & theora
, libopus ? null # Opus de/encoder
, libsndio ? null # sndio playback/record support
, libssh ? null # SFTP protocol
, libtheora ? null # Theora encoder
, libv4l ? null # Video 4 Linux support
, libvdpau ? null # Vdpau hardware acceleration
, libvorbis ? null # Vorbis de/encoding, native encoder exists
, libvpx ? null # VP8 & VP9 de/encoding
, libwebp ? null # WebP encoder
, libX11 ? null # Xlib support
, libxcb ? null # X11 grabbing using XCB
, libxcbshmExtlib ? true # X11 grabbing shm communication
, libxcbxfixesExtlib ? true # X11 grabbing mouse rendering
, libxcbshapeExtlib ? true # X11 grabbing shape rendering
, libXv ? null # Xlib support
, lzma ? null # xz-utils
, nvenc ? false, nvidia-video-sdk ? null # NVIDIA NVENC support
, openal ? null # OpenAL 1.1 capture support
, opencore-amr ? null # AMR-NB de/encoder & AMR-WB decoder
, openglExtlib ? false
, mesa ? null # OpenGL rendering
, openjpeg_2_1 ? null # JPEG 2000 de/encoder
, opensslExtlib ? false, openssl ? null
, libpulseaudio ? null # Pulseaudio input support
, rtmpdump ? null # RTMP[E] support
, samba ? null # Samba protocol
, SDL2 ? null
, shine ? null # Fixed-point MP3 encoder
, soxr ? null # Resampling via soxr
, speex ? null # Speex de/encoder
, vid-stab ? null # Video stabilization
, wavpack ? null # Wavpack encoder
, x264 ? null # H.264/AVC encoder
, x265 ? null # H.265/HEVC encoder
, xavs ? null # AVS encoder
, xvidcore ? null # Xvid encoder, native encoder exists
, zeromq4 ? null # Message passing
, libaom  # AV1 requirement
, zlib ? null
}:


let
  inherit (stdenv.lib) enableFeature;
in

stdenv.mkDerivation rec {
  name = "ffmpeg-${version}";
  version = "4.0";
  src = fetchgit {
    url = "https://git.ffmpeg.org/ffmpeg.git";
    rev = "ace829cb45cff530b8a0aed6adf18f329d7a98f6";
    sha256 = "1055za9dndx9rjq1zhs8ll8v3d8zf7m23frl8q11d7caki7s7yw3";
  };

  configureFlags = [
    # Licensing options (The original file has them as build options but I removed that for simplicity https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/ffmpeg-full/default.nix#L6-L8)
    (enableFeature true "gpl")
    (enableFeature true "version3")
    (enableFeature true "nonfree")
    "--enable-shared --disable-static"
    # Internal libraries
    (enableFeature avcodecLibrary "avcodec")
    (enableFeature avdeviceLibrary "avdevice")
    (enableFeature avfilterLibrary "avfilter")
    (enableFeature avformatLibrary "avformat")
    (enableFeature avresampleLibrary "avresample")
    (enableFeature avutilLibrary "avutil")
    (enableFeature (postprocLibrary && gplLicensing) "postproc")
    (enableFeature swresampleLibrary "swresample")
    (enableFeature swscaleLibrary "swscale")
    # External libraries
    (enableFeature (avisynth != null) "avisynth")
    (enableFeature (bzip2 != null) "bzlib")
    (enableFeature (celt != null) "libcelt")
    (enableFeature (fdkaacExtlib && gplLicensing) "libfdk-aac")
    (enableFeature (fontconfig != null) "fontconfig")
    (enableFeature (freetype != null) "libfreetype")
    (enableFeature (frei0r != null && gplLicensing) "frei0r")
    (enableFeature (fribidi != null) "libfribidi")
    (enableFeature (game-music-emu != null) "libgme")
    (enableFeature (gnutls != null) "gnutls")
    (enableFeature (gsm != null) "libgsm")
    (enableFeature (ladspaH !=null) "ladspa")
    (enableFeature (lame != null) "libmp3lame")
    (enableFeature (libass != null) "libass")
    (enableFeature (libbluray != null) "libbluray")
    (enableFeature (libbs2b != null) "libbs2b")
    (enableFeature (libcaca != null) "libcaca")
    (enableFeature (libdc1394 != null && libraw1394 != null) "libdc1394")
    (enableFeature (libiconv != null) "iconv")
    (enableFeature (libmfx != null) "libmfx")
    (enableFeature (libmodplug != null) "libmodplug")
    (enableFeature (libopus != null) "libopus")
    (enableFeature (libssh != null) "libssh")
    (enableFeature (libtheora != null) "libtheora")
    (enableFeature (libv4l != null) "libv4l2")
    (enableFeature (libvdpau != null) "vdpau")
    (enableFeature (libvorbis != null) "libvorbis")
    (enableFeature (libvpx != null) "libvpx")
    (enableFeature (libwebp != null) "libwebp")
    (enableFeature (libX11 != null && libXv != null) "xlib")
    (enableFeature (libxcb != null) "libxcb")
    (enableFeature libxcbshmExtlib "libxcb-shm")
    (enableFeature libxcbxfixesExtlib "libxcb-xfixes")
    (enableFeature libxcbshapeExtlib "libxcb-shape")
    (enableFeature (lzma != null) "lzma")
    (enableFeature nvenc "nvenc")
    (enableFeature (openal != null) "openal")
    (enableFeature (opencore-amr != null) "libopencore-amrnb")
    (enableFeature openglExtlib "opengl")
    (enableFeature (openjpeg_2_1 != null) "libopenjpeg")
    (enableFeature (opensslExtlib && gplLicensing) "openssl")
    (enableFeature (libpulseaudio != null) "libpulse")
    (enableFeature (rtmpdump != null) "librtmp")
    (enableFeature (shine != null) "libshine")
    (enableFeature (samba != null) "libsmbclient")
    (enableFeature (SDL2 != null) "sdl2")
    (enableFeature (soxr != null) "libsoxr")
    (enableFeature (speex != null) "libspeex")
    (enableFeature (vid-stab != null) "libvidstab") # Actual min. version 2.0
    (enableFeature (wavpack != null) "libwavpack")
    (enableFeature (x264 != null) "libx264")
    (enableFeature (x265 != null) "libx265")
    (enableFeature (xavs != null) "libxavs")
    (enableFeature (xvidcore != null) "libxvid")
    (enableFeature (zeromq4 != null) "libzmq")
    (enableFeature (zlib != null) "zlib")
    (enableFeature (libaom != null) "libaom")
  ];

}

Now the configuration is all set. Let’s move to the building step, We specify two types of build inputs here.

nativeBuildInputs: those dependencies that are only used at build time to generate our code to run at run time.

buildInputs: those are used by the derivation at run-time.

ffmpeg.nix
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{ stdenv
, pkgconfig
, perl
, texinfo
, yasm
...
, zlib ? null
}:


let
  inherit (stdenv.lib) enableFeature;
in

stdenv.mkDerivation rec {
  name = "ffmpeg-${version}";
  version = "4.0";
  src = fetchgit {
    url = "https://git.ffmpeg.org/ffmpeg.git";
    rev = "ace829cb45cff530b8a0aed6adf18f329d7a98f6";
    sha256 = "1055za9dndx9rjq1zhs8ll8v3d8zf7m23frl8q11d7caki7s7yw3";
  };

  configureFlags = [
   ...
  ];

  nativeBuildInputs = [ perl pkgconfig texinfo yasm ];

  # All the dependencies that we have imported at the beginning of the file and enable in configureflags 
  buildInputs = [
    bzip2 celt fontconfig freetype frei0r fribidi game-music-emu gnutls gsm
    libjack2 ladspaH lame libass libbluray libbs2b libcaca libdc1394 libmodplug
    libogg libopus libssh libtheora libvdpau libvorbis libvpx libwebp libX11
    libxcb libXv lzma openal openjpeg_2_1 libpulseaudio rtmpdump opencore-amr makeWrapper
    samba SDL2 soxr openglExtlib mesa speex vid-stab wavpack x264 x265 xavs xvidcore zeromq4 zlib libaom libv4l openssl
  ]
  # Parallel building disabled by default
  enableParallelBuilding = true;
}

Now that should be enough for us to go now. But not really, FFmpeg 4.0 comes with initial support for AV1, which uses libaom. Unfortunately, there’s no already existing nix expression for libaom, so we will write it ourselves. You should be able to understand the next nix expression on your own.

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{ stdenv, fetchgit, yasm, perl, cmake,  pkgconfig }:

stdenv.mkDerivation rec {
  name = "libaom-0.1.0";

  src = fetchgit {
    url = "https://aomedia.googlesource.com/aom";
    rev = "105e9b195bb90c9b06edcbcb13b6232dab6db0b7";
    sha256 = "1fl2sca4df01gyn00s0xcwwirxccfnjppvjdrxdnb8f2naj721by";
  };

  buildInputs = [ perl yasm  ];
  nativeBuildInputs = [ cmake pkgconfig ];

  cmakeFlags = [
    "-DCONFIG_UNIT_TESTS=0"
  ];

}

Next we go to our default.nix file. And we explicitly import the nix expression dependency for libaom into our ffmpeg expression since it doesn’t exist in the nix expressions. Now using libaom inside ffmpeg.nix won’t error.

default.nix
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with import <nixpkgs> {};

rec {
  libaom    = pkgs.callPackage ./libaom.nix {  };
  ffmpeg    = pkgs.callPackage ./ffmpeg.nix { inherit libaom; };
}

Let’s install it finally.

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nix-env -f nix_packages -iA ffmpeg

NOTE: Credit to ffmpeg-full that I used (and edited to be beginner friendly).

Got any feedback? Let me know, please.