;; 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)