659. Teaching during the pandemic, part 2: Recording with two cameras (on linux)

This is a very short post. What if you need to set up two (web)cameras that capture from e.g. different whiteboards?

I had a look at OBS studio, and it's not stable for me. Sometimes I get a cam image, and sometimes I don't. I also had issues with getting two cameras to work. I also looked at webcamoid and cheese. The frame rates were too bad.

What does work for me is guvcview. This is available in the debian repos.

I'll also show you how to sync the sound using KDENLive

1. Install guvcview
sudo apt-get install guvcview

2. Start guvcview.
Then go to video controls.

Select a new Device, then select New

Now you've got both feeds showing:

Then you can simply record:

I won't go into how to switch back and forth between angles in KDENLive. I'll just show you how to sync the videos using the audio:

Import both clips into KDENLive and put them in separate channels. Right-click on one of the tracks, and make it the audio reference:

Align the other clip:

They are now aligned:

Note that you could have done this with a pure audio track as well (we'll get to that in the next post).

You can then start cutting away bits you don't want using the x/scissors:

655. Linux for Edu -- creating lecture videos on linux

We're 'encouraged' to save money on teaching. The easiest (laziest?) way of doing this is to reduce teacher-led time. The ultimate time-saver (in terms of creation of content) is to simply record your lectures using screen-casting.

It's not a very good solution though.

From the point of the lecturer it is not very inspiring, recording 40 minutes of voice-over without mistakes in one take is hard, and updating the slides in the future is hard or impossible. Some solve the voice-over and update issue by using synthetic voices, but they are even more monotonous and uninspiring than most lecturers.

From the point of the student it can be hard to focus for 40 minutes, especially if all you're seeing is a series of slides with a droning voice over. There are other aspects that are bad too: you don't get to interact with the lecturer or your peers, and the lecture content/pace etc. can't be adjusted based on the dynamics of the class.

Some of these aspects can be solved or at least amended by using video editing software. The key is to not simply take a lecture and make a video, but to try to make the most of the medium, without having to become an expert at editing.

Key to making videos is to:
* make them short
...so that students don't need set aside a lot of time to watch them, and can maintain their concentration. It also helps you as a lecturer stay enthusiastic about the video project until it's finished. A long video will make you sick of it before you're done.

* cut everything up into small chunks
...so that you can replace slides and sections, and so you can (re-)record the narration is small chunks. This way you can do as many takes as you need to make sure that the voice over is punchy. No droning!

* to make them engaging
...so that it's fun to watch. This latter bit I haven't cracked. I have decided on a gimmick  though, where I put a countdown timer in the videos. I think/hope that it makes the student feel that the video is moving along quickly and feels 'dynamic'.

Received wisdom dictates that you should include a video of yourself lecturing. There's nothing precluding you from doing that in snippets too and using short Dissolve transitions between the video snippets.


Software:
One should use different tools for different purposes, so I use
* EasyScreenCast or OBSStudio for capturing the desktop if necessary
Make sure to record as webm. Note: You need to transcode the VP8 webm files using the following command or they may show up as black when you render the video in kdenlive:
avconv -i in.webm -c:v libvpx -c:a vorbis -quality best -f webm out.webm

* Audacity for recording audio

* Cheese for recording videos of myself

* Synfig for making simple animation

* kdenlive for video editing

So, here's a quick overview of how to make a simple video using static slides (no screen casting):

1. I made slides in google slides, and then exported each one as a PNG file

2. I recorded the narration using audacity. One recording for each slide. Cut and export.

3. I put it together in kdenlive 
Just drag the length of the slide images to match the lengths of the narration. I also put in a countdown timer as video 2, and overlayed it with the 'composite and transform' transition. I could easily have done the same with a video/videos of myself recorded in cheese.

Either way, the point is that it's very easy to do this.


I also tried to make a simple animation in synfig, but it didn't really pan out. Might be a post in the future -- the students are struggling with visualising 3D objects like orbitals and molecules, and creating animations might help here.