I’ve just published a series of video of a one-day Kubernetes tutorial that I recently delivered in London. I would like to share the method and tools that I used, because although the result is far from perfect, I believe it can be useful for other speakers who want to share their work to a wide audience without a huge investment (in time and equipment).
What are we talking about?
I regularly deliver workshops, tutorials, and other training sessions. The main topics are containers and Kubernetes. Sometimes it is a half-day or full-day workshop at a conference; sometimes a longer tutorial; I also deliver public and private training for various companies.
Speaking of which … Here is a message from our sponsor (i.e. myself)!
In April, I will deliver three training sessions in Paris (in French). There will be getting started with containers, deploying apps with Kubernetes, and Kubernetes administration and operations. French is not your thing? I got you covered with Kubernetes for administrators and operators, a two-day tutorial in June, at the O’Reilly Velocity conference in San Jose (CA). If you know someone who might be interested … I’d love if you could let them know! Thanks ♥
But in-person training doesn’t scale, and I’ve always wanted to reach a wider audience. A lot of high-quality courses are now available online through various platforms. Producing such a course is a lot of work; and for now, I (unfortunately) don’t have the resources to do that.
However, I thought that it should be easier to do a live recording of a workshop, and then make the recording available online. The result wouldn’t be as good as a real online course, but it would be better than nothing (and it would get me one step in the right direction if I ever decide to make such a course after all).
When I was working at Docker Inc., I started recording the workshops I delivered at conferences. To keep things simple, I decided that I would just do a screen recording. Of course, having a camera is better (it’s more engaging to see the speaker) but it’s also way more complex.
When using a Mac, I used Quicktime in “screen recording” mode; when using a Linux machine, I used vokoscreen. I would stop the recording at each break (for coffee and lunch) and start it again before resuming. As a result, at the end of a one-day workshop, I would typically have 4 files, each about 90 minutes long.
These files were a good start, and they were pretty helpful for me to improve my workshops. I don’t know how it is for other speakers, but for me, during the workshop, I always feel like there is one thousand little things that I want to improve (for instance, in the slides) but it’s impossible to take good notes while delivering the workshop at the same time. The video helped me a lot with that.
However, I thought that nobody would want to sit through a 90 minutes video. It’s too long. People probably want to know what’s in the video, and they want to go straight to the part that interests them.
So I wrote a Python script called decoup to help me slice and dice these video files. It works as follows:
- first, I watch the video and write down the start/stop times of each section that I want to isolate, as well as the name of that section;
- then, I run the script, which uses ffmpeg to do the actual cuts, and spit out a number of separate short files.
I use MPlayer to zoom through the video content and write down the start/stop times. It’s pretty efficient, and it typically takes me a few hours to go through one day of content and break it down in sections of about 5 minutes. (The shorter the sections, the more breaks you make, the longer it takes to write down the timestamps.)
If you want to see details about that process, you can check the decoup repository on GitHub.
After getting a bunch of short video files, I upload them to YouTube, and put them all in a playlist.
Here is the result for a Docker Orchestration Workshop that I delivered in December 2016.
It was a good start! But the sound wasn’t great. I was recording using my laptop’s built-in microphone, so the sound would go up and down when I moved around the podium; and when I typed on the keyboard, the keystrokes were really loud. A lot of people brought that up, and I have to admit that it can quickly get on your nerves; even more so when you listen with headphones.
So, I wanted to improve the sound quality.
Improving the sound quality
Spoiler alert: I tried a number of microphones. (No, not the Propellerheads song😎)
The Blue Yeti is a really nice USB mic
I asked around what people were using to record podcasts and similar things, and I was suggested to try the Blue Yeti. I got one, and I recorded myself delivering a very short segment, featuring slides and demos (and therefore, some fast keyboard action). I compared the sound obtained with the internal microphone of a Macbook Air 12, the internal microphone of a Thinkpad T440s, and the Blue Yeti. The Blue Yeti has various modes (mono/omni directional, etc), I tried them all.
Alas, this microphone didn’t help to isolate the sound of my keyboard. Don’t get me wrong: this microphone is amazing. At some point, I set it to stereo and recorded myself walking around the room while talking; and when I played back the recording with my headphones, I could locate myself in space, and it was able to capture faint remote sounds that I hadn’t otherwise noticed. Really impressive! But it also captured my keyboard really well, unfortunately.
Hiring a pro
In September 2018, I delivered a bunch of Kubernetes training sessions with Enix SAS and we hired a pro to capture one session. He also interviewed some of the students.
We had a high-quality camera filming both speakers (there was me, but also Alexandre Buisine), wireless lapel mics, and I was also recording my screen like before.
The videos that we got out of this are of very high quality. Here are just a couple of examples. They are in French, but it will give you an idea of the result:
- a promo video to show the training venue and atmosphere;
- an explanation about declarative and imperative models.
The result is definitely worth it, but it’s a lot of work: you need an extra person during the workshop to film, and then it’s many, many, many hours of work after the workshop to produce the videos.
So I wanted to find something that I could do and re-do without having to hire a pro each time.
Quick aparté: delivering with a co-speaker can make things really tricky if each speaker presents with their own laptop. Now we need the recording from both computers; and if a speaker can intervene while the other is presenting, capturing their voice is another added challenge.
I asked for advice to the best A/V tech I know, Joe Laha. Joe has done A/V for countless conferences and tech events; including recording all the sessions from multiple editions of DevopsDays Minneapolis. Alas, his verdict was loud and clear: if I want to record multiple HDMI sources (and multiple audio inputs) reliably, I need equipment that is (a) expensive (b) bulky. (OK, to be fair, it’s not that bulky, but bigger than I want to fit in my suitcase when traveling.)
Of course, I should have listened to the pro. But I wanted to see for myself, so I bought a tiny, cheap HDMI recorder. Honestly, it’s a nice little gadget, especially for that price. I connected it between my laptop and the videoprojector, inserted an USB key, and voilà, it records my HDMI output.
I thought that I could combine it with a cheap HDMI switcher, and that would give me a way to record two presenters.
Problem: sometimes, the recording would stop. It’s not completely random; I think it happens when the output device (the videoprojector) shuts down. And I think that the projector shuts down when my computer screen saver is on for too long. The recorder has a LED indicating when it is recording, but it’s easy to forget about it.
And, it still doesn’t solve the annoying keyboard noise.
Get more microphones
We did a brief interview with Bret Fisher at a conference, and he used a couple of lapel mics connected to his phone. I thought it was a good idea, so I ordered a pair of cheap lapel mics and gave them a try.
Good news: with these, the noise of the keyboard is almost gone!
There are some downsides, though.
Wires. These are wired mics, meaning that I have to remove or unplug them each time I want to walk away from the podium (during the breaks, for instance). I found that it was only a minor inconvenience. However …
No signal indicator. Obviously, these are just
simple mics, so they don’t have a LED or vu-meter
indicating the strength of the signal. This caused
me two problems. One time, when coming back from the
break, I didn’t plug the mic correctly (the plug wasn’t
all the way in). As a result, on the corresponding
video segment, there is no sound. Oops. Second problem,
since there is no vu-meter, it’s hard to know if you’re
recording at a correct level.
On some videos, my voice is clearly too
loud and saturates the input. It’s not horrible, but
it could have been easily avoided. (By doing a quick
check with a program like
pavucontrol or something
Hum. This problem doesn’t come from the mics themselves, but rather from the mic input on the laptop. On most laptops, these inputs are not properly isolated. As a result, the recording has a 50 Hz (60 Hz in the US) low frequency hum. Unfortunately, disconnecting the laptop AC power didn’t help; it turns out that each time I got a hum, it came from the HDMI, and since the HDMI goes to the projector, disconnecting it is not really an option!
(Note: when my hands are resting on the keyboard’s palm rest, the hum disappears almost entirely. So perhaps I could work something out with e.g. an ESD bracelet?)
Removing the hum
I thought it should be possible to filter out the hum, since it has always the same level, is always in the same frequency bands …
There are a couple of noise filters in recent versions of ffmpeg, but they are not documented properly (or, if you prefer, I was too stupid to understand the docs) and I wasn’t able to get them to work.
However, sox has much better documentation, and I was able to use it to automatically process all my video files.
Here are the steps if you’re interested:
- Using the “decoup” script mentioned above, isolate a few
seconds of noise (i.e. a moment when I don’t speak, and
nobody speaks, and there is just the loud BZZZZ sound).
Let’s say this is
- Extract the sound track from that file:
# This generates noise.wav ffmpeg -i noise.mp4 -vn noise.wav
- Generate a “noise profile” from that file:
# This generates noise.prof sox noise.wav -n noiseprof noise.prof
- Extract the sound track that I want to process:
# This generates video.wav ffmpeg -i video.mp4 -vn video.wav
- Process it with the noise reduction filter:
# This generates filtered.wav sox video.wav filtered.wav noisered noise.prof
- Merge back the filtered audio track with the video:
# This generates video.avi ffmpeg -i video.mp4 -i filtered.wav \ -vcodec copy -acodec copy \ -map 0:v:0 -map 1:a:0 \ video.avi
- Delete the temporary files:
rm video.wav filtered.wav
- Repeat steps 4-7 for all the other files to process.
I work with
.wav files because sox cannot work directly
with compressed audio (at least, not with the audio format
that I have). At the end, I generate a
.avi file because
it’s a flexible container (it can hold the codec from the
.wav file, whereas a
.mp4 file wouldn’t be able to).
It doesn’t really matter to recompress the audio, since I will upload it to YouTube, and YouTube will recompress it anyway.
Upload to YouTube
The most painful part of the whole process is the upload. I couldn’t find an easy way to sort by name the videos in a playlist. I had scripted it a while ago (using Google Spreadsheets, sic!) but I couldn’t find the script this time. So I had to drag all the videos at the right place, one by one.
Ideally, I would also need to edit descriptions and titles en masse, and this doesn’t seem to be possible. I saw a few products that will do it for $$$. I might end up buying one of these, but I would prefer something that I can script easily.
My friend Sébastien Wacquiez (who helped a lot with the logistics for our training sessions in Paris) strongly recommended that I use high-quality, wireless mics. I agree that it would be nice, but when I deliver a workshop by myself (without anyone to help me), I don’t have much time during the breaks, so I’m not even sure that I would have the time to change the batteries.
I’m considering getting a USB lapel mic (this should get rid of the hum, hopefully), or a nice USB audio interface. The latter would hopefully have vu-meters (making sure that I don’t record silence!), and while it sounds a bit overkill, I also do some music recording and mixing once in a while, so it could serve these purposes as well.
Another option (that I will almost certainly do!) is to display a small vu-meter in a corner of the screen. That would hopefully help me to realize immediately when the recording level is too high, or when something is not plugged properly.
I hope that the end result (this Kubernetes workshop video recording) is helpful to many people who want to learn about Kubernetes. And if you like that kind of content and want it delivered to your team or organization, I can totally make that happen!
This is the perfect opportunity to bring up the training sessions that we’re organizing in the coming months!
There will be three sessions in French in April in Paris, and one in English in June in San Jose (CA).
- Bien démarrer avec les containers, April 15-16th, Paris
- Déployer ses applications avec Kubernetes, April 23-24th, Paris
- Opérer et administrer Kubernetes, April 26th, Paris
- Kubernetes for administrators and operators, June 10-11th, San Jose (CA)
I can also deliver private training, customized to your team. Please get in touch if you’re interested!
If you wonder what these training sessions look like, our slides and other materials are publicly available on http://container.training/. You will also find a few videos taken during previous sessions and workshops. This will help you to figure out if this content is what you need.