It's taken a lot longer than I thought.
Partly, this was due to finding new tricks/plugins that improved the process. Partly, it was due to finding unexpected bugs.
However, the main delay came from me not just wanting to do a "do this, then this' tutorial where you come away with no context whatsoever about what's actually happening. I want people who watch the video to get a good idea of what AVISynth is, and what FFMPEG brings to the process.
So, I'd start recording a tutorial, then get caught up in a tangent. An hour and a half later, I still haven't finished the video.
Plus, I make mistakes. There's a lot of material to cover, and I found myself leaving out crucial points (or ones that clear up confusing areas). I could have tried writing out a script, or just patching over my mistakes. However, it turned out that just repeating the actions so many times that you can practically do them in your sleep eventually got me to the right place. I still had some audio issues to address in post, but my overall presentation quality is much improved from earlier attempts.
I could try adding more production values than just a screencast. But at a certain point, you just have to release a project. So, here without further ado is my first full-length tutorial. Because the total video is around 45 minutes, I will probably add chapter links on the video at a later point. For now, though, here is my work. Constructive criticism is welcome.
Here's a written description of the process, including links: