Add generic streaming interpreter with configurable sources/audio

- Add stream_sexp_generic.py: fully generic sexp interpreter
- Add streaming primitives for video sources and audio analysis
- Add config system for external sources and audio files
- Add templates for reusable scans and macros
- Fix video/audio stream mapping in file output
- Add dynamic source cycling based on sources array length
- Remove old Python effect files (migrated to sexp)
- Update sexp effects to use namespaced primitives

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

sexp_effects/effects/blend.sexp

@@ -1,56 +1,31 @@
-;; Blend effect - combines two video streams
-;; Multi-input effect: uses frame-a and frame-b
+;; Blend effect - combines two video frames
+;; Streaming-compatible: frame is background, overlay is second frame
+;; Usage: (blend background overlay :opacity 0.5 :mode "alpha")
+;;
 ;; Params:
 ;;   mode - blend mode (add, multiply, screen, overlay, difference, lighten, darken, alpha)
 ;;   opacity - blend amount (0-1)
-;;   resize_mode - how to resize frame-b to match frame-a (fit, crop, stretch)
-;;   priority - which dimension takes priority (width, height)
-;;   pad_color - color for padding in fit mode [r g b]
 
-(require-primitives "image" "blending")
+(require-primitives "image" "blending" "core")
 
 (define-effect blend
   :params (
-    (mode :type string :default "overlay")
+    (overlay :type frame :default nil)
+    (mode :type string :default "alpha")
     (opacity :type float :default 0.5)
-    (resize_mode :type string :default "fit")
-    (priority :type string :default "width")
-    (pad_color :type list :default (quote [0 0 0]))
   )
-  (let [a frame-a
-        a-w (width a)
-        a-h (height a)
-        b-raw frame-b
-        b-w (width b-raw)
-        b-h (height b-raw)
-        ;; Calculate scale based on resize mode and priority
-        scale-w (/ a-w b-w)
-        scale-h (/ a-h b-h)
-        scale (if (= resize_mode "stretch")
-                1  ;; Will use explicit dimensions
-                (if (= resize_mode "crop")
-                  (max scale-w scale-h)  ;; Scale to cover, then crop
-                  (if (= priority "width")
-                    scale-w
-                    scale-h)))
-        ;; For stretch, use target dimensions directly
-        new-w (if (= resize_mode "stretch") a-w (round (* b-w scale)))
-        new-h (if (= resize_mode "stretch") a-h (round (* b-h scale)))
-        ;; Resize b
-        b-resized (resize b-raw new-w new-h "linear")
-        ;; Handle fit (pad) or crop to exact size
-        b (if (= resize_mode "crop")
-            ;; Crop to center
-            (let [cx (/ (- new-w a-w) 2)
-                  cy (/ (- new-h a-h) 2)]
-              (crop b-resized cx cy a-w a-h))
-            (if (and (= resize_mode "fit") (or (!= new-w a-w) (!= new-h a-h)))
-              ;; Pad to center
-              (let [pad-x (/ (- a-w new-w) 2)
-                    pad-y (/ (- a-h new-h) 2)
-                    canvas (make-image a-w a-h pad_color)]
-                (paste canvas b-resized pad-x pad-y))
-              b-resized))]
-    (if (= mode "alpha")
-      (blend-images a b opacity)
-      (blend-images a (blend-mode a b mode) opacity))))
+  (if (core:is-nil overlay)
+    frame
+    (let [a frame
+          b overlay
+          a-h (image:height a)
+          a-w (image:width a)
+          b-h (image:height b)
+          b-w (image:width b)
+          ;; Resize b to match a if needed
+          b-sized (if (and (= a-w b-w) (= a-h b-h))
+                    b
+                    (image:resize b a-w a-h "linear"))]
+      (if (= mode "alpha")
+        (blending:blend-images a b-sized opacity)
+        (blending:blend-images a (blending:blend-mode a b-sized mode) opacity)))))