Retrospectively, I chose the “wrong” option of recording my lectures than simply doing live online teaching when the university asked us in Feb. about the preferred teaching method during the outbreak. It took me much much more time than I expected to record the lectures. The results have not been that great but some students do appreciate the video lectures: at least they can double or triple the playing speed if bored… Respect to all the MOOC teachers…

Anyway, after recording my lectures on Modal Logic for almost the whole semester, below is what I have settled down with… It is perhaps the simplest but easy-to-edit solution for recording (-generated) technical lectures (on a Mac) without requiring any experience in video editing (though see tips below for tricky things).

(The general method of using PPT with exported images of a PDF was recommended to me by my colleague Shengyang Zhong based on a Zhihu post. Many thanks! BTW our university bought group licenses of the relevant Microsoft software mentioned below.)

What you need:

• Powerpoint (Windows version, preferably Office 2019 edition). The latest Mac version (16.35) still lacks features that are crucial for recording a technical lecture (the stared steps below). For Mac users, it perhaps worths installing a Windows 10 virtual machine.
• Preferably a pen tablet or a touch screen (for drawings/writings to explain the technical/mathematical contents). See below the tips for Mac users about the touch screen.

Basic Steps:

1. Prepare your slides in PDF using (usually beamerclass).
2. Export the slides as a collection of JPG image files. You can choose the suitable resolution of the exported JPGs.
3. *Create a new presentation in Powerpoint and import the image files by Insert -> Photo Album (a new page for each picture).
4. Delete the title page of the album, and make the images full-page by adjusting the size of the slides by Design -> Slide Size.
5. *Record your lecture using Slide Show -> Record Slide Show with your drawings (and the camera video of yourself). You can stop at any moment, and redo any slide individually.
6. Export the file as an MP4 video file.
7. Compress (or adjust slightly) the video using some (open-source) software like HandBrake, if needed.

Advantages of this approach:

• No video editing experience/software is required.
• You can record/edit each slide individually. The video camera can be turned on and off as you wish (at a corner of your slides).
• A slide is simply an image thus you don’t have the trouble of converting -generated formulas, compared to methods turning a beamer-generated PDF into a PPT file directly.
• Powerpoint itself can convert the narrated file into a reasonable MP4 video, and the PPT file (much smaller than the video) is also helpful for many since it can be played in Powerpoint.

Important tips:

• There is a short gap in voice recording during the transitions of the slides. This becomes more noticeable if you use lots of \pause for your listed items in the beamer-based PDF slides.
• To overcome the above drawback, you may make serval images appear one after another in one slide by animation upon clicks. However, I do not recommend doing so in general, since the narration in the same slide is recorded as a single file. If you want to just change the recording for one item on the slide, it is basically impossible without recording the whole thing again.
• You can trim the voice recording on each slide by clicking the speaker icon on the slide and use Audio Tools -> Playback. The editing you can do this way is quite limited, and often causes a crash of PPT (at least in my case).
• Using the hotkeys for drawing pen and the “laser” pointer is helpful during recording. You cannot create a white screen during the recording (but you can do so during a live presentation).
• If you want to add something to a recorded slide, the easiest way is to duplicate that slide and make the recorded drawing on the duplicated slide into a picture. Then you can record the additional things on the duplicated slide. In playback of the recording, it looks like you are still on the same slide.
• Don’t forget to save your PPT on a regular basis, the auto-save function might not work properly!

Tips particularly for Mac users:

• The current Mac versions of PPT cannot record drawings but it can open/play/export PPT files with recorded drawings. This means once you finish recording in the Windows virtual machine, you can simply use your Mac PPT to export it as an MP4 video (it is much faster than doing it in a virtual machine).
• Using a (Wacom) pen tablet is OK for drawing (don’t forget to connect the device via your virtual machine), but not perfect, since you may have problems as I do of synchronizing your hands and eyes to make drawings/writings right on the spot on the slides… It is a pity that there is no Mac with a touch screen.
• However, you can connect an external touch screen to a Mac and just write on the screen (also for the Windows virtual machine)! Not sure whether connecting to an iPad Pro (I don’t have one) can help for the virtual machine… After searching for a while, I ended up with a 23.8” NEWTAP touch screen (I believe Dell and Viewsonic also make such screens) which is partially supported by my Macbook pro (select the color profile SD 170M-A for the monitor if it looks purple). However, due to perhaps some driver problem, when I connect it to the Windows virtual machine (I am using VMware fusion), the touch function will be magically switched off after being idle for just one minute…
• Finally, I found a powerful software called UPDD which can drive the external touch screen on a Mac and support multi-touch/gestures for many applications beautifully (you may use a Mac like a Surface). The problem of the one-minute idling thing also went away. However (again and again), it seems that the UPDD driver overrides the default Mac driver, but it cannot work properly with some online whiteboards I am using, such as AWWapp and Shimo (although UPDD does have some patches).
• The final kick was made by the very helpful customer service of UPDD: instead of stoping all the processes of UPDD (which will freeze the touch screen), we can simply stop the UPDD commander, and then the MacOS driver will take over to handle the touches, which works fine with those online whiteboards. Done!