Scripting FFmpeg to move text in y co-ordinate by

Question

I'm using the basic drawtext command like this

ffmpeg -i output.mp4 -vf \
'drawtext=textfile='textfile.txt':x=0:y=0 \
:fontsize=30:fontcolor=white:borderw=3 \
:bordercolor=black:box=0' output.mp4"

which puts stationary text at location (x, y) = (0,0)

What I want to do is move this text by 10 points in y plane at certain time codes.

at 00:00:10, y would be 0
at 00:00:11, y would be 10
at 00:00:43, y would be 20
...
...
at 00:10:44, y would be 30

so the 'y' co-ordinate has a fix increment of 10 at 'keytimes'

Is there a way to do that?

Answer 1

Basic method is to use an expression of the form,

y='lte(t,10.99)*0+between(t,11,42.99)*10+between(t,43,643.99)*20+gte(t,644)*30'

Each sub-expression is of the form of time-qualification * position and only one time-qualification evaluates to 1 for any segment of the timeline.