LPR tweaks (#17783)

* clarify docs

* improve debugging messages

* don't run any lpr postprocessing

* wording

docs/docs/configuration/license_plate_recognition.md

@@ -184,7 +184,7 @@ cameras:
     ffmpeg: ... # add your streams
     detect:
       enabled: True
-      fps: 5 # increase to 10 if vehicles move quickly across your frame. Higher than 10 is unnecessary and is not recommended.
+      fps: 5 # increase to 10 if vehicles move quickly across your frame. Higher than 15 is unnecessary and is not recommended.
       min_initialized: 2
       width: 1920
       height: 1080
@@ -267,7 +267,7 @@ With this setup:
 - Review items will always be classified as a `detection`.
 - Snapshots will always be saved.
 - Zones and object masks are **not** used.
-- The `frigate/events` MQTT topic will **not** publish tracked object updates, though `frigate/reviews` will if recordings are enabled.
+- The `frigate/events` MQTT topic will **not** publish tracked object updates with the license plate bounding box and score, though `frigate/reviews` will publish if recordings are enabled. If a plate is recognized as a known plate, publishing will occur with an updated `sub_label` field. If characters are recognized, publishing will occur with an updated `recognized_license_plate` field.
 - License plate snapshots are saved at the highest-scoring moment and appear in Explore.
 - Debug view will not show `license_plate` bounding boxes.
 
@@ -280,7 +280,7 @@ With this setup:
 | Object Detection        | Standard Frigate+ detection applies                    | Bypasses standard object detection                              |
 | Zones & Object Masks    | Supported                                              | Not supported                                                   |
 | Debug View              | May show `license_plate` bounding boxes                | May **not** show `license_plate` bounding boxes                 |
-| MQTT `frigate/events`   | Publishes tracked object updates                       | Does **not** publish tracked object updates                     |
+| MQTT `frigate/events`   | Publishes tracked object updates                       | Publishes limited updates                                       |
 | Explore                 | Recognized plates available in More Filters            | Recognized plates available in More Filters                     |
 
 By selecting the appropriate configuration, users can optimize their dedicated LPR cameras based on whether they are using a Frigate+ model or the secondary LPR pipeline.

frigate/config/config.py

@@ -513,10 +513,14 @@ class FrigateConfig(FrigateBaseModel):
                     )
 
             # Warn if detect fps > 10
-            if camera_config.detect.fps > 10:
+            if camera_config.detect.fps > 10 and camera_config.type != "lpr":
                 logger.warning(
                     f"{camera_config.name} detect fps is set to {camera_config.detect.fps}. This does NOT need to match your camera's frame rate. High values could lead to reduced performance. Recommended value is 5."
                 )
+            if camera_config.detect.fps > 15 and camera_config.type == "lpr":
+                logger.warning(
+                    f"{camera_config.name} detect fps is set to {camera_config.detect.fps}. This does NOT need to match your camera's frame rate. High values could lead to reduced performance. Recommended value for LPR cameras are between 5-15."
+                )
 
             # Default min_initialized configuration
             min_initialized = int(camera_config.detect.fps / 2)

frigate/data_processing/common/license_plate/mixin.py

@@ -490,10 +490,6 @@ class LicensePlateProcessingMixin:
                 merged_boxes.append(current_box)
                 current_box = next_box
 
-            logger.debug(
-                f"Provided plate_width: {plate_width}, max_gap: {max_gap}, horizontal_gap: {horizontal_gap}"
-            )
-
         # Add the last box
         merged_boxes.append(current_box)
 
@@ -1133,7 +1129,7 @@ class LicensePlateProcessingMixin:
         # 4. Log the comparison
         logger.debug(
             f"Plate comparison - Current: {top_plate} (score: {curr_score:.3f}, min_conf: {curr_min_conf:.2f}) vs "
-            f"Previous: {prev_plate} (score: {prev_score:.3f}, min_conf: {prev_min_conf:.2f})\n"
+            f"Previous: {prev_plate} (score: {prev_score:.3f}, min_conf: {prev_min_conf:.2f}) "
             f"Metrics - Length: {len(top_plate)} vs {len(prev_plate)} (scores: {curr_length_score:.2f} vs {prev_length_score:.2f}), "
             f"Area: {top_area} vs {prev_area}, "
             f"Avg Conf: {avg_confidence:.2f} vs {prev_avg_confidence:.2f}, "
@@ -1263,6 +1259,15 @@ class LicensePlateProcessingMixin:
                 )
                 return
 
+            # don't run for objects with no position changes
+            # this is the initial state after registering a new tracked object
+            # LPR will run 2 frames after detect.min_initialized is reached
+            if obj_data.get("position_changes", 0) == 0:
+                logger.debug(
+                    f"{camera}: Plate detected in {self.config.cameras[camera].detect.min_initialized + 1} concurrent frames, LPR frame threshold ({self.config.cameras[camera].detect.min_initialized + 2})"
+                )
+                return
+
             license_plate: Optional[dict[str, any]] = None
 
             if "license_plate" not in self.config.cameras[camera].objects.track:
@@ -1401,6 +1406,8 @@ class LicensePlateProcessingMixin:
                     license_plate_frame,
                 )
 
+        logger.debug(f"{camera}: Running plate recognition.")
+
         # run detection, returns results sorted by confidence, best first
         start = datetime.datetime.now().timestamp()
         license_plates, confidences, areas = self._process_license_plate(

frigate/data_processing/post/license_plate.py

@@ -54,6 +54,9 @@ class LicensePlatePostProcessor(LicensePlateProcessingMixin, PostProcessorApi):
         Returns:
             None.
         """
+        # don't run LPR post processing for now
+        return
+
         event_id = data["event_id"]
         camera_name = data["camera"]
 

frigate/track/tracked_object.py

@@ -138,11 +138,13 @@ class TrackedObject:
 
         if not self.false_positive and has_valid_frame:
             # determine if this frame is a better thumbnail
-            if self.thumbnail_data is None or is_better_thumbnail(
-                self.obj_data["label"],
-                self.thumbnail_data,
-                obj_data,
-                self.camera_config.frame_shape,
+            if self.thumbnail_data is None or (
+                better_thumb := is_better_thumbnail(
+                    self.obj_data["label"],
+                    self.thumbnail_data,
+                    obj_data,
+                    self.camera_config.frame_shape,
+                )
             ):
                 # use the current frame time if the object's frame time isn't in the frame cache
                 selected_frame_time = (
@@ -150,6 +152,13 @@ class TrackedObject:
                     if obj_data["frame_time"] not in self.frame_cache.keys()
                     else obj_data["frame_time"]
                 )
+                if (
+                    obj_data["frame_time"] not in self.frame_cache.keys()
+                    and not better_thumb
+                ):
+                    logger.warning(
+                        f"Frame time {obj_data['frame_time']} not in frame cache, using current frame time {selected_frame_time}"
+                    )
                 self.thumbnail_data = {
                     "frame_time": selected_frame_time,
                     "box": obj_data["box"],