How to add subtitles in other places

The zoompan filter expressions are evaluated each frame. The variables referenced in the expressions contain the last calculated value, or the default if it's the first frame.

The value of the evaluated zoom expression represents the ratio of the resulting dimensions to the original dimensions i.e. zoom = 3 means the zoom window has a third of the width and height of the input.

x and y represent where the top-left corner of the zoom window is placed within the input image.

d is the duration in frames that the zoom is evaluated and applied.

You should, as a matter of course, specify the output framerate fps and size s of the filter (see its documentation), else the filter will apply its defaults of 25 fps and 1280x720, which may not be what you want.

For smooth zooms, you may need to upscale the image beforehand.