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/apple_handler.py

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+from .base_handler import VendorHandler
+
+class AppleHandler(VendorHandler):
+    """
+    Handles Apple-specific HEIC features.
+    Apple's motion photos (Live Photos) are stored in a separate MOV file,
+    so we won't find an embedded video here.
+    """
+    # We override the method to make it explicit that Apple files are handled,
+    # even though the result is the same as the base class.
+    def find_motion_photo_offset(self, heic_file) -> int | None:
+        # We could add logic here later to find the ContentIdentifier
+        print("Apple HEIC detected. Motion photo video is in a separate .mov file, not embedded.")
+        return None

handlers/base_handler.py

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+from __future__ import annotations
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from heic_file import HEICFile
+
+class VendorHandler:
+    """
+    Abstract base class for vendor-specific logic.
+    """
+    def find_motion_photo_offset(self, heic_file: HEICFile) -> int | None:
+        """
+        Tries to find the byte offset of the embedded motion photo video.
+        Returns the offset if found, otherwise None.
+        """
+        # Default behavior: no motion photo found.
+        return None

handlers/samsung_handler.py

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+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