Export Video Directly from Powerpoint (Macro)

Sub MkVideo()
If ActivePresentation.CreateVideoStatus <> ppMediaTaskStatusInProgress Then
ActivePresentation.CreateVideo FileName:=Environ("USERPROFILE") & "\Desktop\test.mp4", _
UseTimingsAndNarrations:=True, _
VertResolution:=1080, _
FramesPerSecond:=25, _
Quality:=100
Else: MsgBox "There is another conversion to video in progress"
End If
End Sub

To have a webm that's shorter than the 5 second minimum:
Transitions Tab > Advance Slide (advance to end, technically), set to After: length of video or presentation

Copy, paste, hit ESC, Go to View > Macros, select the macro named "MkVideo" and then hit "Run"

Regedit 150 DPI trick
https://support.microsoft.com/en-ca/help/827745/how-to-change-the-export-resolution-of-a-powerpoint-slide

Find image
Open in GIMP and change DPI via Image > Print Size
Set DPI to 150 both H and V
Export as PNG
Put in Powerpoint
Caption as normal
Export as PNG, back into GIMP to trim via Wand > White Space > Invert Selection > Fit to Selection
Use crop to content instead, much easier and cleaner, just watch out for white backgrounds where it can trim to letters instead of the white border.

Libreoffice - 96DPI?

Powerpoint Animated Captions

To have text typewriter across screen, click arrow under Effect Options:

Effect:
Sound: No Sound
After Animation: Don't Dim

Timing:
Start: After Previous
Delay: 1.5 seconds
Delay between letters: 0.03
 
Text Animation:
Group text: By 1st Level Paragraphs
Animate attached shape: on


Set timings manually for slide transition after selecting play after or change after