实现 AppleHandler 和 SamsungHandler 类，处理特定于供应商的 HEIC 特性，添加查找嵌入视频的逻辑

handlers/samsung_handler.py

@@ -0,0 +1,17 @@
+from .base_handler import VendorHandler
+
+class SamsungHandler(VendorHandler):
+    """Handles Samsung-specific HEIC features, like the embedded mpvd box."""
+
+    def find_motion_photo_offset(self, heic_file) -> int | None:
+        """
+        Searches for the 'mpvd' box which contains the video data.
+        """
+        for box in heic_file.boxes:
+            if box.type == 'mpvd':
+                print(f"Samsung 'mpvd' box found at offset {box.offset}")
+                # The video data starts right after the box header.
+                return box.offset + 8 
+        
+        print("Samsung HEIC detected, but no 'mpvd' box found.")
+        return None