Recording a conference presentation
2020/06/23 by Armin Pournaki

I recorded a presentation for the IC2S2 2020 and wanted to keep track of the steps for future presentations.

1. Split up the presentation pdf using ImageMagick’s convert:

   % convert -quality 100 -density 600 FILENAME.pdf single%d.png
   

2. In OBS, add an “Image Slideshow” source to your canvas, choosing the freshly created png sequence.
3. Add your camera or webcam as a source.
4. If you only need to record a presentation, you are good to go. If you need to do a showcase like in my example of the twitter explorer, I recommend creating a second scene, where you add the display capture or window. You can just copy-paste the webcam from one scene to the other so it will stay at the exact same position.
5. Set keyboard shortcuts in the OBS settings. I chose the following:
   • N next slide
   • P previous slide
   • Ctrl + Shift + R record
   • Ctrl + Shift + P pause
   • Ctrl + Shift + S stop
   • Ctrl + Shift + N switch to scene 2

I recommend recording in 1080p 60fps mkv if your computer can handle it. While using Image Slideshow, you can overlay any window on your desktop screen from which you can read your notes if needed. If you make a mistake, don’t stop the recording but make a pause, maybe clap and continue from where you left off. The bad parts will be cut out later.

Now that you have your large mkv file, you can cut it in losslesscut. It is nice because you don’t have to re-encode before or after cutting. Typing h displays all the commands you need to know.

In the case of IC2S2 (and maybe other conferences), I had to submit the video file as mp4. Luckily, switching from mkv to mp4 is just a matter of changing the container, which can be achieved using the following ffmpeg-command:

% ffmpeg -i FILENAME.mkv -codec copy FILENAME.mp4