mpv, ffmpeg: use addOpenGLRunpath to fix CUDA-accelerated playback

This fixes #67780.

Currently, using `mpv --hwdec=nvdec --msg-level=vd=debug` on NVIDIA results in:

```
[vd] Opening decoder hevc
[vd] Looking at hwdec hevc-nvdec...
Cannot load libcuda.so.1
[vd] Could not create device.
[vd] No hardware decoding available for this codec.
```

With just mpv patched, ffmpeg cannot load libnvcuvid.so.1:

```
[vd] Opening decoder hevc
[vd] Looking at hwdec hevc-nvdec...
[vd] Trying hardware decoding via hevc-nvdec.
[vd] Selected codec: hevc (HEVC (High Efficiency Video Coding))
[vd] Pixel formats supported by decoder: vaapi_vld cuda yuv420p10le
[vd] Codec profile: Main 10 (0x2)
[vd] Requesting pixfmt 'cuda' from decoder.
[ffmpeg/video] hevc: Cannot load libnvcuvid.so.1
[ffmpeg/video] hevc: Failed loading nvcuvid.
[ffmpeg/video] hevc: Failed setup for format cuda: hwaccel initialisation returned error.
```

With both mpv and ffmpeg patched, it works:

```
[vd] Opening decoder hevc
[vd] Looking at hwdec hevc-nvdec...
[vd] Trying hardware decoding via hevc-nvdec.
[vd] Selected codec: hevc (HEVC (High Efficiency Video Coding))
[vd] Pixel formats supported by decoder: vaapi_vld cuda yuv420p10le
[vd] Codec profile: Main 10 (0x2)
[vd] Requesting pixfmt 'cuda' from decoder.
Using hardware decoding (nvdec).
[vd] Decoder format: 3840x2160 cuda[p010] bt.2020-ncl/bt.2020/pq/limited/auto SP=10.000000 CL=unknown (auto 0.000000/0.000000/0.000000)
```

1 files changed, 7 insertions, 3 deletions

diff --git a/pkgs/development/libraries/ffmpeg/generic.nix b/pkgs/development/libraries/ffmpeg/generic.nix
index 4c0ca0210cc..b3310e44ae0 100644
--- a/pkgs/development/libraries/ffmpeg/generic.nix
+++ b/pkgs/development/libraries/ffmpeg/generic.nix
@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, pkgconfig, perl, texinfo, yasm
+{ stdenv, fetchurl, pkgconfig, addOpenGLRunpath, perl, texinfo, yasm
 , alsaLib, bzip2, fontconfig, freetype, gnutls, libiconv, lame, libass, libogg
 , libssh, libtheora, libva, libdrm, libvorbis, libvpx, lzma, libpulseaudio, soxr
 , x264, x265, xvidcore, zlib, libopus, speex, nv-codec-headers, dav1d
@@ -42,7 +42,7 @@
 
 let
   inherit (stdenv) isDarwin isFreeBSD isLinux isAarch32;
-  inherit (stdenv.lib) optional optionals enableFeature;
+  inherit (stdenv.lib) optional optionals optionalString enableFeature;
 
   cmpVer = builtins.compareVersions;
   reqMin = requiredVersion: (cmpVer requiredVersion branch != 1);
@@ -157,7 +157,7 @@ stdenv.mkDerivation rec {
       "--enable-cross-compile"
   ] ++ optional stdenv.cc.isClang "--cc=clang";
 
-  nativeBuildInputs = [ perl pkgconfig texinfo yasm ];
+  nativeBuildInputs = [ addOpenGLRunpath perl pkgconfig texinfo yasm ];
 
   buildInputs = [
     bzip2 fontconfig freetype gnutls libiconv lame libass libogg libssh libtheora
@@ -186,6 +186,10 @@ stdenv.mkDerivation rec {
       substituteInPlace $pc \
         --replace "includedir=$out" "includedir=''${!outputInclude}"
     done
+  '' + optionalString stdenv.isLinux ''
+    # Set RUNPATH so that libnvcuvid in /run/opengl-driver(-32)/lib can be found.
+    # See the explanation in addOpenGLRunpath.
+    addOpenGLRunpath $out/lib/libavcodec.so*
   '';
 
   installFlags = [ "install-man" ];