fix sytax error

api/main.py

@@ -139,8 +139,8 @@ def protected(request: Request, Authorize: AuthJWT = Depends()):
     for row in db.query(statement):
         video_info_list.append({'id':row['id'],'title':row['name'],'duration':row['duration'],'url':row['url']})
     dic_return = {'user_info':{'userName':current_user,'email':user_obj['email'],'video_num':video_num,'total_sec':total_sec,'left_sec':user_obj['left_time']},'video_info':video_info_list}
-
-    return str(dic_return)
+    str_return = json.dumps(dic_return)
+    return str_return
 
 # login & register page
 @app.get("/login", response_class=HTMLResponse)