Add optional idle heartbeat for Birdseye (#20453)

* Add optional idle heartbeat for Birdseye (periodic frame emission when idle)

birdseye: add optional idle heartbeat and FFmpeg tuning envs (default off)

This adds an optional configuration field `birdseye.idle_heartbeat_fps` to
enable a lightweight idle heartbeat mechanism in Birdseye. When set to a value
greater than 0, Birdseye periodically re-sends the last composed frame during
idle periods (no motion or active updates).

This helps downstream consumers such as go2rtc, Alexa, or Scrypted to attach
faster and maintain a low-latency RTSP stream when the system is idle.

Key details:
- Config-based (`birdseye.idle_heartbeat_fps`), default `0` (disabled).
- Uses existing Birdseye rendering pipeline; minimal performance impact.
- Does not alter behavior when unset.

Documentation: added tip section in docs/configuration/restream.md.

* Update docs/docs/configuration/restream.md

Co-authored-by: Nicolas Mowen <nickmowen213@gmail.com>

* Update docs/docs/configuration/reference.md

Co-authored-by: Nicolas Mowen <nickmowen213@gmail.com>

* Refactors Birdseye idle frame broadcasting

Simplifies the idle frame broadcasting logic by removing the dedicated thread.

The idle frame is now resent directly within the main loop,
improving efficiency and reducing complexity.  Also, limits the idle
heartbeat FPS to a maximum of 10 since the framebuffer is limited to 10 anyway

* ruff fix

---------

Co-authored-by: Nicolas Mowen <nickmowen213@gmail.com>
Co-authored-by: Francesco Durighetto <francesco.durighetto@subbyx.com>
Co-authored-by: duri <duri@homelabubuntu.durihome.unifi>

docs/docs/configuration/reference.md

@@ -240,6 +240,8 @@ birdseye:
     scaling_factor: 2.0
     # Optional: Maximum number of cameras to show at one time, showing the most recent (default: show all cameras)
     max_cameras: 1
+  # Optional: Frames-per-second to re-send the last composed Birdseye frame when idle (no motion or active updates). (default: shown below)
+  idle_heartbeat_fps: 0.0
 
 # Optional: ffmpeg configuration
 # More information about presets at https://docs.frigate.video/configuration/ffmpeg_presets

docs/docs/configuration/restream.md

@@ -24,6 +24,11 @@ birdseye:
   restream: True
 ```
 
+:::tip 
+
+To improve connection speed when using Birdseye via restream you can enable a small idle heartbeat by setting `birdseye.idle_heartbeat_fps` to a low value (e.g. `1–2`).  This makes Frigate periodically push the last frame even when no motion is detected, reducing initial connection latency.
+
+:::
 ### Securing Restream With Authentication
 
 The go2rtc restream can be secured with RTSP based username / password authentication. Ex:
@@ -164,4 +169,4 @@ NOTE: The output will need to be passed with two curly braces `{{output}}`
 go2rtc:
   streams:
     stream1: exec:ffmpeg -hide_banner -re -stream_loop -1 -i /media/BigBuckBunny.mp4 -c copy -rtsp_transport tcp -f rtsp {{output}}
-```
+```

frigate/config/camera/birdseye.py

@@ -55,6 +55,12 @@ class BirdseyeConfig(FrigateBaseModel):
     layout: BirdseyeLayoutConfig = Field(
         default_factory=BirdseyeLayoutConfig, title="Birdseye Layout Config"
     )
+    idle_heartbeat_fps: float = Field(
+        default=0.0,
+        ge=0.0,
+        le=10.0,
+        title="Idle heartbeat FPS (0 disables, max 10)",
+    )
 
 
 # uses BaseModel because some global attributes are not available at the camera level

frigate/output/birdseye.py

@@ -9,6 +9,7 @@ import os
 import queue
 import subprocess as sp
 import threading
+import time
 import traceback
 from typing import Any, Optional
 
@@ -791,6 +792,10 @@ class Birdseye:
         self.frame_manager = SharedMemoryFrameManager()
         self.stop_event = stop_event
         self.requestor = InterProcessRequestor()
+        self.idle_fps: float = self.config.birdseye.idle_heartbeat_fps
+        self._idle_interval: Optional[float] = (
+            (1.0 / self.idle_fps) if self.idle_fps > 0 else None
+        )
 
         if config.birdseye.restream:
             self.birdseye_buffer = self.frame_manager.create(
@@ -848,6 +853,15 @@ class Birdseye:
             if frame_layout_changed:
                 coordinates = self.birdseye_manager.get_camera_coordinates()
                 self.requestor.send_data(UPDATE_BIRDSEYE_LAYOUT, coordinates)
+        if self._idle_interval:
+            now = time.monotonic()
+            is_idle = len(self.birdseye_manager.camera_layout) == 0
+            if (
+                is_idle
+                and (now - self.birdseye_manager.last_output_time)
+                >= self._idle_interval
+            ):
+                self.__send_new_frame()
 
     def stop(self) -> None:
         self.converter.join()