Initial commit: video effects processing system

Add S-expression based video effects pipeline with modular effect
definitions, constructs, and recipe files.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

effects/echo.sexp

@@ -0,0 +1,21 @@
+;; Echo effect - temporal ghosting/trails
+;; Usage: python3 plan.py effects/echo.sexp -p num_echoes=4 -p decay=0.5 | python3 execute.py - -d . -o output.mp4
+;;
+;; Parameters:
+;;   num_echoes: number of ghost frames (1 to 10, default: 4)
+;;   decay: fade rate per echo (0.2 to 0.9, default: 0.5)
+
+(recipe "echo"
+  :version "1.0"
+  :encoding (:codec "libx264" :crf 20 :preset "medium" :audio-codec "aac" :fps 30)
+
+  (effect echo :path "sexp_effects/effects/echo.sexp")
+
+  ;; Default parameters (overridden by -p num_echoes=N -p decay=N)
+  (def num_echoes 4)
+  (def decay 0.5)
+
+  (def video (source :path "monday.webm"))
+  (def clip (-> video (segment :start 0 :duration 10)))
+  (def result (-> clip (effect echo :num_echoes num_echoes :decay decay)))
+  result)