add audio-abtest script

pkgs/audio-abtest/default.nix

@@ -0,0 +1,11 @@
+{writeShellScriptBin}:
+writeShellScriptBin "audio-abtest" ''
+  track_1=$(shuf -i 0-1 -n 1)
+  track_2=$(( 1 - track_1 ))
+
+  ffmpeg -i "$1" -i "$2" -f lavfi -i color=c=black:s=100x100:r=3 \
+    -c:v libx264 -tune stillimage -b:v 100k \
+    -c:a copy \
+    -map $track_1:a:0 -map $track_2:a:0 -map 2:v:0 \
+    -shortest output.mkv
+''

pkgs/default.nix

@@ -4,5 +4,6 @@
     ida-pro = pkgs.callPackage ./ida-pro {};
     cartograph-cf = pkgs.callPackage ./cartograph-cf {};
     keyboard-state = pkgs.callPackage ./keyboard-state {};
+    audio-abtest = pkgs.callPackage ./audio-abtest {};
   };
 }