ffmpeg: Make letters appear one at the time, like a typewriter
Typewriter effect on ffmpeg using an .ass file, I generated this gif using the following line:
ffmpeg -f lavfi -i color=size=640x480:rate=30:color=black -vf &quot;subtitles=typewriter.ass&quot; -t 8 ffmpeg_typewriter.gif


I used the Eagisub program to get the parameters used in karaoke !! I created two styles (style1 and style2) both with different fonts, background etc. The shadow colors, background colors were chosen transparent because they appear however transparent, and the time of {\Kn} defines the character display time or time of the word or phrase, just change the n as long as you want !!! Too simple !! follow the file generated on Eagisub that can be easily edited by hand !! That's it thanks !!
    [Script Info]
; Script generated by Aegisub 3.2.2
; http://www.aegisub.org/
Title: Default Aegisub file
ScriptType: v4.00+

[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
Style: style1,Ubuntu Mono,100,&amp;H00FFFFFF,&amp;HFF0000FF,&amp;HFF000000,&amp;H00000000,0,0,0,0,100,100,0,0,1,0,0,4,10,10,10,1
Style: style2,DejaVu Sans Mono,37,&amp;H00FFFFFF,&amp;HFF0000FF,&amp;HFF000000,&amp;H00000000,0,0,0,0,100,100,0,0,1,0,0,4,10,10,10,1

[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:01.10,0:00:12.00,style1,,0,0,0,,{\pos(109,187.5)}{\k25}H{\k25}e{\k25}l{\k25}l{\k10}o{\k15}!{\k15}\NI{\k15}'{\k15}m{\k15} D{\k15}i{\k15}v{\k15}e{\k15}r{\k15}s{\k15}a{\k15}l{\k15}i{\k15}z{\k15}a{\k15}n{\k15}d{\k15}o{\k15}!{\k15}!
Dialogue: 0,0:00:05.50,0:00:09.40,style2,,0,0,0,,{\k15\pos(108,374)}Editing{\k15} a {\k15}.ass {\k15}with {\k15}Aegisub {\k15}to\N {\k15}generate {\k15}the {\k15}typewriter {\k15}effect.