[FFmpeg-user] Filter complex problem

[JULIAN GARDNER]

I have this filter

-filter_complex '[0:#$dvbsPid] scale=1280:720 [sub],[0:v][sub] overlay'

which is taking in a known 1280:720 video, resizing the dvb subtitles to 1280:720 and overlaying the 2.

PROBLEM
I dont want to have this 1280:720 fixed, what i would like is to be able to use some form of [0:v]:iw:[0:v];ih, but this does not work

So is there a way of getting the [0:v] inputs width and height to i can change the filter to be a generic filter

joolz