660. Teaching in the pandemic, part 3: What I'll be doing to capture live lectures. Audio.

I've looked at a few different solutions, but I've basically settled on recording video and audio separately. The downside of this is that I won't stream. The advantage is that I can do post-processing to add clearer pictures of slides etc.

The video part is pretty straight forward. See e.g. http://verahill.blogspot.com/2020/07/659-teaching-during-pandemic-part-2.html

When it comes to audio I've explored a range of solutions:

* Bluetooth headset -- this would've allowed me to stream, but the sound quality is just too poor with bluetooth (I tried Blueparrot B350-XT). For an example of how bad it can be, check out this corporate(!) video:

Advantage: wireless, can stream, only covers one ear
Disadvantage: Sound quality

* 2.4 GHz Wireless headset -- I tested Logitech G930. The sound quality is OK, but it covers both ears, and makes it hard/ uncomfortable to deal with a live audience.
Advantage: sound quality, wireless, can stream
Disadvantage: shuts out the live audience

* 'Normal' microphones -- I have a number of microphones, including Blue Yeti. Many of them are wired (USB), and none of them will work in capturing a moving (i.e. mobile) lecturer.
Advantage: superior audio -- when very close, streaming
Disadvantage: poor audio unless you're right in front of the mic

* Mobile phone lavalier mic -- See here for how to do that: http://verahill.blogspot.com/2020/07/658-teaching-during-pandemic-part-1-how.html.
Advantage: great sound, mobile, can potentially stream
Disadvantage: drains phone battery, can be tricky to set up LAN, if using receiving device (laptop) as hotspot you may not be able to connect to the internet (i.e. can't stream)

My chosen solution:
* Using a portable audio recorder (e.g. dictaphone) --  I've got a Zoom H1n, and a lavalier microphone. I love this microphone. It's lightweight, portable, not too expensive, and the internal XY microphone is great (to my ears). The amplifier for external mics is a bit weak, but it works for my purposes, especially if you post-process in Audacity. But that leaves you having to sync your video and your audio in post. I've already showed you how easy it is to do that here: http://verahill.blogspot.com/2020/07/659-teaching-during-pandemic-part-2.html

Note that you need to invest in a decent lavalier microphone as well. Also note that most these days seem to come with a 3.5 mm TRRS connector (good for mobile phones), and the Zoom needs 3.5 mm TRS (the old standard). Many of the cheap/affordable lavalier mics that you find on e.g. Amazon come with TRS/TRRS adapters, so it's not much of an issue.

Advantage: potentially great sound, great battery life
Disadvantage: you can't stream live, needs a lavalier microphone

So there we are -- I'll set up a single webcam to record video directly to my laptop. I'll capture the sound using it as well, but mostly to help me sync the audio later. I'll record my voice using a dictaphone and a lavalier microphone, post-process the sound in Audacity, then import video and audio in KDENLive, where I'll sync everything. I can then add pictures of my slides as well, and don't have to worry about the image quality during recording.

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.

654. Screen-casting on linux (debian 9)

Minipost:
I'm interested in making course videos where I show my desktop (I might have a full-screen presentation going), but where I also want to show my face.

I'm using debian.

Solution:
To screen-cast the desktop I'm using EasyScreenCast, which is a Gnome Extension: https://extensions.gnome.org/extension/690/easyscreencast/

Not much to say about it really, other than that it works very well.

To get my face on the desktop I use guvcview, which is in the repos.

To make guvcview stay on top even during a full-screen presentation I followed this: https://www.linuxquestions.org/questions/linux-general-1/how-to-make-guvcview-stay-always-on-top-4175541777/

My son's orca lecturing on the importance of experiments in formulating new theories

kdenlive seems like an interesting editor for post-production, but I haven't got that far yet.

492. Briefly: fixing no sound when playing youtube videos in chrome, iceweasel/firefox

Not sure what caused this, but I suddenly had no sound when playing flash videos in the browser.

Playing flv files using e.g. mplayer works fine. I'm using pulseaudio, and have an ~/.asoundrc file:

pcm.!default.type pulse
ctl.!default.type pulse

alsamixer is working fine and the channels are unmuted.

The solution:
I moved ~/.macromedia to ~/.xmacromedia as suggested at the end of this post: https://bbs.archlinux.org/viewtopic.php?id=134892.

Didn't even need to restart the browser -- suddenly everything worked.

The question is why is there a ~/.macromedia folder, and what does it do? Might have a look into that at some later point.