Streaming my PhD defense on YouTube

Jun 10, 2021

In this post, I describe the setup I used for my PhD defense. The jury and I were in a video-conference with BigBlueButton (BBB) software, the defense was also live-streamed on YouTube for the public. The resulting video can be found here.

My system

Some steps may differ, depending on your hardware and operating system. I used my laptop, a Dell Latitude 5480 with an Intel i7-7820HQ CPU and 16 GB of memory. The operating system was Debian 10, with Linux kernel 4.19.0-16-amd64.

The defense was streamed with the OBS software. I installed it with the usual apt install and got the package version 22.0.3+dfsg1-1.

What to stream?

Initially, I wanted to directly stream the BBB window, for convenience. In BBB you can upload the PDF of your slides and make your entire presentation within BBB, with a nice dot pointer.

When I uploaded my slides however, BBB did not render them properly, the font was wrong. My slides were done using LaTeX and Beamer, with the Metropolis theme, which uses Fira font. I fixed this by rasterizing the slides, as follows (based on this post): 

convert -density 600 +antialias slides.pdf output.pdf
gs -q -dNOPAUSE -dBATCH -dPDFSETTINGS=/prepress -sDEVICE=pdfwrite -sOutputFile=slides_rasterized.pdf output.pdf && rm output.pdf

However, I was unhappy about the result, I found the slides in the YouTube stream not so pretty. In the end, I changed my setup. Instead of uploading the slides to BBB I shared my screen, and instead of streaming the BBB window I streamed the PDF viewer window.

I was used to the default PDF viewer on my system, evince. Thanks to my advisor, I discovered the impressive viewer, which is much better for a presentation. I launched it with this command: 

impressive --noquit --tracking -T 100 -t Crossfade --fake-fullscreen -g 1920x1080 slides.pdf

Pro-tip: in impressive, use Enter to focus on something and Z to zoom. Also, read the man-page, it has a lot of very nice features.

OBS setup

I describe here how I configured OBS itself.

General settings

In File then Parameter, I changed a few things.

  • In the Stream tab, I selected YouTube/YouTube Gaming. Here, I entered the stream key (obtained from YouTube Studio).
  • In the Output tab, I changed the bitrate to 6000 (the default one was too low, YouTube gave a warning).
  • In the Video tab, I changed both the base resolution and the output resolution to 1920x1080. I also changed the FPS to 30.

Scenes

As I said, the defense was carried on BigBlueButton and streamed on YouTube. I created four different scenes in OBS with various layouts.

  1. Welcome scene, used at the very start of the stream. I used an image (my first slide), with no camera and no audio.
  2. Deliberation scene, used while the jury is deliberating. I used a different image (a photo with a written text), with no camera and no audio.
  3. Discussion scene, used during the questions of the jury. I used a window capture (Xcomposite) of my Firefox window with BBB, cropped by 150px at the top to remove the URL.
  4. Presentation scene, used during my talk. I used a window capture (Xcomposite) of my PDF viewer and I added my webcam on the side (video capture V4L2). Important: I needed to disable video buffering for the camera, otherwise it was not properly synchronized with the rest (double-click on the source, then scroll down and untick the box).

In both the scenes 3 and 4, I also had two audio sources. I had the audio output of my laptop (PulseAudio) to hear the jury and my microphone (Alsa).

In all scenes I needed to mute the two default audio sources that appear in the audio mixer, to truly have no audio in the first two scenes and only the audio I selected in the two last scenes.

Using the webcam on several applications simultaneously

As described above, I needed to use my webcam in two different applications, Firefox (for BBB) and OBS. This is not possible natively. To fix that, I found this tutorial and this question.

First, install the kernel module: 

sudo apt install v4l2loopback-dkms v4l2loopback-utils ffmpeg

Load the kernel module and create /dev/video5: 

sudo modprobe v4l2loopback exclusive_caps=1 video_nr=5  # creates `/dev/video5`

Send the webcam to the virtual device: 

ffmpeg -i /dev/video0 -f v4l2 -codec:v rawvideo -pix_fmt yuv420p /dev/video5

Then, we can choose the "dummy device" instead of the default camera in BBB and OBS.

Note: sometimes, when I started Firefox with BBB, for some reason it used the hardware device for the webcam instead of asking me or using the dummy device. Here the solution was to revoke the authorization to use the camera, so that it asks again.

Reduce the microphone noise

I used a good microphone (see next section), but still had some white noise in the background. To fix this, we can process the audio with pulseaudio.

I used two links, this question and this documentation.

I simply added this line in the file /etc/pulse/default.pa: 

load-module module-echo-cancel source_name=noise_cancelled source_properties=device.description=noise_cancelled

Note that we can pass several arguments to the module. This line was enough for me, but more fancy configurations are possible.

Then, simply go to the OS parameters to change the audio input source and choose noise_cancelled.

Audio hardware

In my very first rehearsals, I used the integrated microphone of my laptop. As expected, the sound was terrible.

I have at home a nice little microphone for my camera (the Rode VideoMicro), so I started to use it, which gave much better results.

My laptop had only one jack entry and I needed to plug both the microphone and the earphone (I could not use the speakers of the laptop, to avoid any echo). Hence, I bought a cheap adapter.

With this setup, the sound of my microphone was not very good, I could hear some echo. My guess is that the cheap adapter is crappy and we have signal interferences between the input and the output. Fortunately, I had at home a USB DAC headphone amplifier (the FiiO Olympus 2 E10K). Thus, I could plug my earphones on this amplifier and my microphone directly on the laptop jack entry, without using the adapter. This is obviously an overkill solution, but this worked well.

An easy alternative would be to use a headset with an integrated microphone, but I did not have this at home.