Update ui/callbacks.py

ui/callbacks.py

@@ -4,16 +4,17 @@
 ---------------------------------
 All functions here are *thin* wrappers wired to the Gradio interface.
 
-Changes in this revision
-------------------------
-•   Added **key_color_mode** positional arg to `cb_process_video`
-    (matches the new dropdown in ui_components.py)
-•   Passes that value straight through to `process_video_fixed(...)`
+• key_color_mode parameter already added (matches ui_components.py)
+• PREVIEW FUNCTIONS NOW IMPLEMENTED:
+    - cb_video_changed        → returns first frame
+    - cb_custom_bg_preview    → returns uploaded image
 """
 
 from __future__ import annotations
-import os
+import os, cv2                             # ← cv2 was already needed by fallback gen
 from typing import Any, Dict, Tuple
+import numpy as np
+from PIL import Image
 
 # ---- Core pipeline wrappers (from core/app.py) ----
 from core.app import (
@@ -211,10 +212,35 @@ def cb_use_gen_bg(path_text: str):
 
 
 # ------------------------------------------------------------------
-# PREVIEWS (safe no-ops — extend later)
+# PREVIEWS
 # ------------------------------------------------------------------
 def cb_video_changed(vid_path: str):
-    return None
+    """
+    Extract first frame of the uploaded video for a quick preview.
+    Returns a numpy RGB array (Gradio will display it).
+    """
+    try:
+        if not vid_path:
+            return None
+        cap = cv2.VideoCapture(vid_path)
+        ok, frame = cap.read()
+        cap.release()
+        if not ok:
+            return None
+        # Convert BGR→RGB for correct colours in the browser
+        frame_rgb = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
+        return frame_rgb
+    except Exception:
+        return None
 
 def cb_custom_bg_preview(file_obj: dict | None):
+    """
+    Display the uploaded background image (if any) as a preview.
+    """
+    try:
+        if file_obj and file_obj.get("name"):
+            img = Image.open(file_obj["name"]).convert("RGB")
+            return np.array(img)
+    except Exception:
+        pass
     return None