Windows Movie Maker file size

Question

I'm using ShareX to make x.264/MP4 tutorial videos in which there is very little motion. Most of the time I'm just typing and highlighting text. I'm getting reasonable file sizes.

I edit the videos in Windows Movie Maker. There don't seem to be settings that preserve quality without multiplying the file size by about 3. These are the settings I'm using.

FFmpeg:

-y -rtbufsize 100M -f gdigrab -framerate 8 -offset_x 0 -offset_y 0
-video_size 1920x1080 -draw_mouse 1 -i desktop -f dshow -i
audio="Microphone (Realtek High Defini" -c:v libx264 -r 8 -preset
faster -tune zerolatency -crf 30 -pix_fmt yuv420p -c:a libvo_aacenc
-ac 2 -b:a 96k "output.mp4"

Movie Maker:

Width: 1920 pixels
Height: 1080 pixels
Bit rate: 800 kbps
Frame rate: 8 fps

If I set the bit rate much less than this, I get terrible artifacts.

What can I do? I have no choice about the output format, by the way.