add helperfunction to crop slides

modules/home/zsh/functions.zsh

@@ -0,0 +1,16 @@
+# helper function to crop cs3223 slides
+crop_slides() {
+  input="$1"
+  if [ -z "$input" ]; then
+    echo "Usage: crop_slides <inputfile>"
+    return 1
+  fi
+
+  # Get base name (without extension)
+  base="${input%.*}"
+  output="${base}-slides.mp4"
+
+  # Crop left 2/3 of a 1280x640 video (≈853 px wide)
+  nix run "nixpkgs#ffmpeg" -- -i "$input" -filter:v "crop=853:640:0:0" -c:a copy "$output"
+}
+