Caption Size

Sets the font size for burn-in captions.

video-caption-size accepts either:

• An integer in pixels — the absolute font size in pixels, applied to the output video at its encoded resolution.
• A fraction of the video height — a decimal value between 0.0 and 1.0 that sets the font size relative to the output frame height. For example, 0.05 sets the font size to 5% of the video height.

Using a fractional value ensures captions remain proportionally sized regardless of the output resolution.