Limited shm frame count (#12346)

* Only keep 2x detect fps frames in SHM

* Don't delete previous shm frames in output

* Catch case where images do not exist

* Ensure files are closed

* Clear out all frames when shutting down

* Correct the number of frames saved

* Simplify empty shm error handling

* Improve frame safety

frigate/output/output.py

@@ -45,7 +45,6 @@ def output_frames(
     signal.signal(signal.SIGINT, receiveSignal)
 
     frame_manager = SharedMemoryFrameManager()
-    previous_frames = {}
 
     # start a websocket server on 8082
     WebSocketWSGIHandler.http_version = "1.1"
@@ -97,6 +96,9 @@ def output_frames(
 
         frame = frame_manager.get(frame_id, config.cameras[camera].frame_shape_yuv)
 
+        if frame is None:
+            continue
+
         # send camera frame to ffmpeg process if websockets are connected
         if any(
             ws.environ["PATH_INFO"].endswith(camera) for ws in websocket_server.manager
@@ -124,12 +126,7 @@ def output_frames(
         preview_recorders[camera].write_data(
             current_tracked_objects, motion_boxes, frame_time, frame
         )
-
-        # delete frames after they have been used for output
-        if camera in previous_frames:
-            frame_manager.delete(f"{camera}{previous_frames[camera]}")
-
-        previous_frames[camera] = frame_time
+        frame_manager.close(frame_id)
 
     move_preview_frames("clips")
 
@@ -149,7 +146,7 @@ def output_frames(
 
         frame_id = f"{camera}{frame_time}"
         frame = frame_manager.get(frame_id, config.cameras[camera].frame_shape_yuv)
-        frame_manager.delete(frame_id)
+        frame_manager.close(frame_id)
 
     detection_subscriber.stop()