Background writing frames to disk; put them in a dir; start from 0 to…

… more easily use ffmpeg to create videos from them

lib/ferrum/screencaster.rb

@@ -1,24 +1,45 @@
 # frozen_string_literal: true
+require 'fileutils'
 
+# Combine the resulting frames together into a video with:
+# ffmpeg -y -framerate 30 -i 'frame-%d.jpeg' -c:v libx264 -r 30 -pix_fmt yuv420p try2.mp4
+#
 module Ferrum
   class Screencaster
     def initialize(page)
       @page = page
+      @frame_number = 0
+      @threads = []
+      @base_dir = ""
     end
 
     def add_frame(params)
       warn "frame"
+
       @page.command("Page.screencastFrameAck", sessionId: params["sessionId"])
 
-      ts = (Time.now.to_f * 1000).to_i
-      File.binwrite("img_#{ts}.jpeg", Base64.decode64(params["data"]))
+      t = Thread.new { File.binwrite("#{recordings_dir}/frame-#{@frame_number}.jpeg", Base64.decode64(params["data"])) }
+      @frame_number += 1
+      @threads << t
+      true
+    end
+
+    def recordings_dir
+      return @recordings_dir if defined? @recordings_dir
+
+      session_id = @page.client.session_id
+      @recordings_dir = FileUtils.mkdir_p("#{@base_dir}/screencast_recordings/#{session_id}/").first
+      @recordings_dir
     end
 
-    def start_screencast
+    def start_screencast(base_dir = "")
+      @base_dir = base_dir
       @page.command("Page.startScreencast", format: "jpeg")
     end
 
     def stop_screencast
+      warn "joining threads"
+      @threads.each(&:join)
       warn "stopped"
       @page.command("Page.stopScreencast")
     end