Preview webcam pendant capture DSLR (pas de freeze entre les poses)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/main.py

@@ -5,6 +5,8 @@ import logging
 from pathlib import Path
 from contextlib import asynccontextmanager
 
+import cv2
+
 from fastapi import FastAPI, WebSocket, WebSocketDisconnect, UploadFile, File
 from fastapi.responses import FileResponse, JSONResponse
 from fastapi.staticfiles import StaticFiles
@@ -506,6 +508,14 @@ async def traiter_message_ws(msg: dict, ws: WebSocket):
     if type_msg == "ping":
         await ws.send_json({"type": "pong"})
     elif type_msg == "preview":
+        # Pendant une capture DSLR, utiliser directement la webcam fallback
+        donnees = None
+        if capture_en_cours and camera._preview_webcam_fallback:
+            ret, frame = camera._preview_webcam_fallback.read()
+            if ret:
+                _, buf = cv2.imencode(".jpg", frame, [cv2.IMWRITE_JPEG_QUALITY, 70])
+                donnees = buf.tobytes()
+        else:
             donnees = camera.preview()
         if donnees:
             b64 = base64.b64encode(donnees).decode("ascii")