Day 11 — reveal-notes + tmux + keylogger = present-notes

Today I spent most of my time recording the talk video for PyConline AU. I wanted to use present and since it doesn't have a speaker notes view right now, I managed to hack together a way to make the reveal.js speaker notes work with present. It worked out surpisingly well!

tmux to the rescue! Since it is configured to use 8 colors by default, I had to set it to use 256 colors (for better images) by adding set -g default-terminal "screen-256color" to the ~/.tmux.conf. After that, I started a new tmux session with tmux new-session -s 1 and ran present in it. I also had to set tmux set-option status off to remove the status bar at the bottom. Post that, I opened the reveal.js speaker notes view in the browser.

Since both present and reveal.js support SPACEBAR to move to the next slide, I needed a way to detect this keypress at a global level, otherwise it would only change the slide on the window that was in focus. So I wrote this keylogger which ran tmux send-keys -t 1 ' ' (whenever SPACEBAR was pressed on the reveal.js speaker notes view) to change the slide in the session where present was running.

  # -*- coding: utf-8 -*-

  import os
  import pyxhook


  def OnKeyPress(event):
      if event.Key.lower() == "space":
          os.system("tmux send-keys -t 1 ' '")


  new_hook = pyxhook.HookManager()
  new_hook.KeyDown = OnKeyPress
  new_hook.HookKeyboard()

  try:
      new_hook.start()
  except KeyboardInterrupt:
      pass

Yes it is a hack, but it worked great. I've finally recorded a talk about terminals and CLIs, in a terminal using a CLI!

I used OBS Studio to record the video, and ffmpeg to crop the two takes and join them. I love open source software!

Here are the ffmpeg cropping commands. I did it in two steps for each take because I didn't want to do the mental math to calculate the -t duration required to crop the videos.

  $ ffmpeg -i 2020-08-25\ 01-31-40.mp4 -ss 00:01:36 -async 1 output1.mp4
  $ ffmpeg -i output1.mp4 -t 00:15:28 -async 1 output2.mp4
  $ ffmpeg -i 2020-08-25\ 02-42-37.mp4 -ss 00:00:33 -async 1 output3.mp4
  $ ffmpeg -i output3.mp4 -t 00:07:28 -async 1 output4.mp4

And here is the ffmpeg concat command, which assumes the existence of a file called concat.txt containing a list of all the files that need to be joined. (output2.mp4 and output4.mp4 in this case)

  $ ffmpeg -f concat -i concat.txt -c copy output5.mp4

Tomorrow I want to dig into the Rust book!