Add ffmpeg and ffcheck helper script

hosts/marauder/default.nix

@@ -1,5 +1,9 @@
 { self, pkgs, inputs, secrets, ... }:
-{
+let
+  ffcheck = pkgs.writeShellScriptBin "ffcheck" ''
+    ${pkgs.ffmpeg}/bin/ffmpeg -v error -stats -hide_banner -i "$1" -c copy -f null -
+  '';
+in {
   imports = [
     self.nixosModules.common
     self.nixosModules.prompt
@@ -77,6 +81,8 @@
 
     # Multimedia
     vlc
+    ffmpeg
+    ffcheck
 
     # Productivity
     obsidian