Replace green screen with error message and force camera_fps to 0 (#4544)

* Move to images specific folder

* Send error image when camera stream is not available

* Immediately set camera_fps to 0 if camera crashes

* Cache error image so it is not read from file system on each run

* Move camera fps set

frigate/video.py

@@ -242,6 +242,7 @@ class CameraWatchdog(threading.Thread):
             now = datetime.datetime.now().timestamp()
 
             if not self.capture_thread.is_alive():
+                self.camera_fps.value = 0
                 self.logger.error(
                     f"Ffmpeg process crashed unexpectedly for {self.camera_name}."
                 )
@@ -251,6 +252,7 @@ class CameraWatchdog(threading.Thread):
                 self.logpipe.dump()
                 self.start_ffmpeg_detect()
             elif now - self.capture_thread.current_frame.value > 20:
+                self.camera_fps.value = 0
                 self.logger.info(
                     f"No frames received from {self.camera_name} in 20 seconds. Exiting ffmpeg..."
                 )