preload video poster upon page load

lib/veloroute_web/endpoint.ex

@@ -16,7 +16,8 @@ defmodule VelorouteWeb.Endpoint do
     websocket: true,
     longpoll: false
 
-  socket "/live", Phoenix.LiveView.Socket, websocket: [connect_info: [session: @session_options]]
+  socket "/live", Phoenix.LiveView.Socket,
+    websocket: [connect_info: [:user_agent, session: @session_options]]
 
   plug Video.ServePlug
   plug Esri.Tiles

lib/veloroute_web/live/frame_live.ex

@@ -249,6 +249,7 @@ defmodule VelorouteWeb.FrameLive do
           socket
           |> update_map_bounds(params)
           |> VelorouteWeb.Live.VideoState.maybe_update_video(article, params)
+          |> VelorouteWeb.Live.VideoState.maybe_preload_video_poster()
           |> maybe_autoplay(params["autoplay"] == "true")
 
     socket =

lib/veloroute_web/live/video_state.ex

@@ -266,6 +266,35 @@ defmodule VelorouteWeb.Live.VideoState do
     end
   end
 
+  def maybe_preload_video_poster(%{assigns: %{video_hash: hash, video_start: start_ms}} = socket) do
+    if !test_env?() && !Phoenix.LiveView.connected?(socket) && valid_hash(hash) &&
+         start_ms != nil && !probably_robot?(socket) do
+      Logger.debug("video poster async load start #{hash} #{start_ms}")
+
+      Task.start(VelorouteWeb.ImageExtractController, :extract, [
+        hash,
+        start_ms,
+        start_ms,
+        :webp
+      ])
+    end
+
+    socket
+  end
+
+  def maybe_preload_video_poster(socket), do: socket
+
+  defp test_env?() do
+    Application.get_env(:veloroute, :env) == :test
+  end
+
+  defp probably_robot?(socket) do
+    ua = Phoenix.LiveView.get_connect_info(socket, :user_agent) |> String.downcase()
+
+    ["http://", "https://", "bot", "ows.eu/owler", "python-requests", "okhttp"]
+    |> Enum.any?(&String.contains?(ua, &1))
+  end
+
   @spec position_from_time(Phoenix.LiveView.Socket.t(), %{binary() => binary()}) ::
           Video.Rendered.indicator() | nil
   defp position_from_time(%{assigns: %{video: state}}, params) do

lib/warmup.ex

@@ -44,7 +44,7 @@ defmodule Warmup do
   end
 
   defp initial_video_poster() do
-    Task.start_link(fn ->
+    Task.start(fn ->
       with {hash, ts} <- VelorouteWeb.Live.VideoState.default_video_poster() do
         VelorouteWeb.ImageExtractController.extract(hash, ts, ts, :webp)
       end