[scene_detector] Make detector interface an ABC and cleanup properties

Author: Breakthrough

scenedetect/detector.py

@@ -25,6 +25,7 @@
 """
 
 import typing as ty
+from abc import ABC, abstractmethod
 from enum import Enum
 
 import numpy
@@ -33,36 +34,18 @@
 from scenedetect.stats_manager import StatsManager
 
 
-class SceneDetector:
+class SceneDetector(ABC):
     """Base class to inherit from when implementing a scene detection algorithm.
 
     This API is not yet stable and subject to change.
     """
 
-    # TODO(v0.7): Make this a proper abstract base class.
+    def __init__(self):
+        self._stats_manager: ty.Optional[StatsManager] = None
 
-    # TODO(v0.7): This should be a property.
-    stats_manager: ty.Optional[StatsManager] = None
-    """Optional :class:`StatsManager <scenedetect.stats_manager.StatsManager>` to
-    use for caching frame metrics to and from."""
-
-    def stats_manager_required(self) -> bool:
-        """Stats Manager Required: Prototype indicating if detector requires stats.
-
-        Returns:
-            True if a StatsManager is required for the detector, False otherwise.
-        """
-        return False
-
-    def get_metrics(self) -> ty.List[str]:
-        """Returns a list of all metric names/keys used by this detector.
-
-        Returns:
-            List of strings of frame metric key names that will be used by
-            the detector when a StatsManager is passed to process_frame.
-        """
-        return []
+    # Required Methods
 
+    @abstractmethod
     def process_frame(
         self, timecode: FrameTimecode, frame_img: numpy.ndarray
     ) -> ty.List[FrameTimecode]:
@@ -75,7 +58,8 @@ def process_frame(
         Returns:
            List of timecodes where scene cuts have been detected, if any.
         """
-        return []
+
+    # Optional Methods
 
     def post_process(self, timecode: int) -> ty.List[FrameTimecode]:
         """Called after there are no more frames to process.
@@ -95,6 +79,30 @@ def event_buffer_length(self) -> int:
         """
         return 0
 
+    # Frame Stats/Metrics
+
+    @property
+    def stats_manager(self) -> ty.Optional[StatsManager]:
+        """Optional :class:`StatsManager <scenedetect.stats_manager.StatsManager>` to use for
+        storing frame metrics. When this detector is added to a parent
+        :class:`SceneManager <scenedetect.scene_manager.SceneManager>`, then this is set to the
+        same :class:`StatsManager <scenedetect.stats_manager.StatsManager>` of the parent - but
+        only if it has one itself."""
+        return self._stats_manager
+
+    @stats_manager.setter
+    def stats_manager(self, value: ty.Optional[StatsManager]):
+        self._stats_manager = value
+
+    def get_metrics(self) -> ty.List[str]:
+        """Returns a list of all metric names/keys used by this detector.
+
+        Returns:
+            List of strings of frame metric key names that will be used by
+            the detector when a StatsManager is passed to process_frame.
+        """
+        return []
+
 
 class FlashFilter:
     """Filters fast-cuts to enforce minimum scene length."""

scenedetect/scene_manager.py

@@ -313,9 +313,6 @@ def add_detector(self, detector: SceneDetector) -> None:
         Arguments:
             detector (SceneDetector): Scene detector to add to the SceneManager.
         """
-        if self._stats_manager is None and detector.stats_manager_required():
-            assert not self._detector_list
-            self._stats_manager = StatsManager()
 
         detector.stats_manager = self._stats_manager
         if self._stats_manager is not None:

website/pages/changelog.md

@@ -703,6 +703,8 @@ Although there have been minimal changes to most API examples, there are several
  * Remove deprecated `AdaptiveDetector.get_content_val()` method (the same information can be obtained using a `StatsManager`)
  * Remove deprecated `AdaptiveDetector` constructor argument `min_delta_hsv` (use `min_content_val` instead)
  * Remove `advance` parameter from `VideoStream.read()` (was always set to `True`, callers should handle caching frames now if required)
+ * Remove `SceneDetector.stats_manager_required` property as it is no longer required
+ * Remove `SceneDetector` is now a Python abstract class (`abc.ABC`) but all method names remain the same
 
  #### General