Add ability to restream birdseye (#4761)

* Try using RTSP for restream

* Add ability to get snapshot of birdseye when birdseye restream is enabled

* Write to pipe instead of encoding mpeg1

* Write to cache instead

* Use const for location

* Formatting

* Add hardware encoding for birdseye based on ffmpeg preset

* Provide framerate

* Adjust args

* Fix order

* Delete pipe file if it exists

* Cleanup spacing

* Fix spacing

docs/docs/configuration/restream.md

@@ -7,6 +7,14 @@ title: Restream
 
 Frigate can restream your video feed as an RTSP feed for other applications such as Home Assistant to utilize it at `rtsp://<frigate_host>:8554/<camera_name>`. Port 8554 must be open. [This allows you to use a video feed for detection in frigate and Home Assistant live view at the same time without having to make two separate connections to the camera](#reduce-connections-to-camera). The video feed is copied from the original video feed directly to avoid re-encoding. This feed does not include any annotation by Frigate.
 
+#### Force Audio
+
+Different live view technologies (ex: MSE, WebRTC) support different audio codecs. The `restream -> force_audio` flag tells the restream to make multiple streams available so that all live view technologies are supported. Some camera streams don't work well with this, in which case `restream -> force_audio` should be disabled.
+
+#### Birdseye Restream
+
+Birdseye RTSP restream can be enabled at `restream -> birdseye` and accessed at `rtsp://<frigate_host>:8554/birdseye`. Enabling the restream will cause birdseye to run 24/7 which may increase CPU usage somewhat.
+
 ### RTMP (Deprecated)
 
 In previous Frigate versions RTMP was used for re-streaming. RTMP has disadvantages however including being incompatible with H.265, high bitrates, and certain audio codecs. RTMP is deprecated and it is recommended to move to the new restream role.