av1an: vapoursynth support

Corrected wrapper entries:
 - Need to override vapoursynth with `vapoursynth.withPlugins` for av1an to be able to use VS plugins. Changed PYTHON_PATH accordingly.  Passing `pkgs.vapoursynth` to `python3Packages.makePythonPath` makes an incorrect path entry, resulting in segfault when the program is run.
 - Need LD_LIBRARY_PATH to use VS plugins (e.g. ffms2 and lsmash, the recommended chunking method). Otherwise get e.g. `Error: FFMS2 is not installed, but it was specified as the chunk method`.
 - Need vapoursynth in PATH to use VS based chunking methods or VS script as input. At least, `vspipe` binary needs to be visible in PATH.

Add mkvtoolnix option; it is the recommended concatenation method.

pkgs/by-name/av/av1an/package.nix

@@ -5,7 +5,7 @@
   testers,
   av1an-unwrapped,
   ffmpeg,
-  python3Packages,
+  python3,
   libaom,
   svt-av1,
   rav1e,
@@ -13,6 +13,8 @@
   x264,
   x265,
   libvmaf,
+  vapoursynth,
+  mkvtoolnix-cli,
   withAom ? true, # AV1 reference encoder
   withSvtav1 ? false, # AV1 encoder/decoder (focused on speed and correctness)
   withRav1e ? false, # AV1 encoder (focused on speed and safety)
@@ -20,6 +22,7 @@
   withX264 ? true, # H.264/AVC encoder
   withX265 ? true, # H.265/HEVC encoder
   withVmaf ? false, # Perceptual video quality assessment algorithm
+  withMkvtoolnix ? true, # mkv editor, recommended concatenation method
 }:
 # av1an requires at least one encoder
 assert lib.assertMsg (lib.elem true [
@@ -40,19 +43,24 @@ symlinkJoin {
   postBuild =
     let
       runtimePrograms =
-        [ (ffmpeg.override { inherit withVmaf; }) ]
+        [
+          vapoursynth
+          (ffmpeg.override { inherit withVmaf; })
+        ]
         ++ lib.optional withAom libaom
         ++ lib.optional withSvtav1 svt-av1
         ++ lib.optional withRav1e rav1e
         ++ lib.optional withVpx libvpx
         ++ lib.optional withX264 x264
         ++ lib.optional withX265 x265
-        ++ lib.optional withVmaf libvmaf;
+        ++ lib.optional withVmaf libvmaf
+        ++ lib.optional withMkvtoolnix mkvtoolnix-cli;
     in
     ''
       wrapProgram $out/bin/av1an \
+        --prefix LD_LIBRARY_PATH : ${vapoursynth}/lib \
         --prefix PATH : ${lib.makeBinPath runtimePrograms} \
-        --prefix PYTHONPATH : ${python3Packages.makePythonPath [ python3Packages.vapoursynth ]}
+        --prefix PYTHONPATH : ${vapoursynth}/${python3.sitePackages}
     '';
 
   passthru = {