How can I split each PDF page into two pages, using the command line?

I have a few ebooks scanned from originals. They're formatted so that a single *PDF page* contains two *actual pages*: one on the left, and one on the right. I want to programmatically split each PDF page into two, so the left 50% of PDF page 1 becomes page 1 and its right becomes page 2, and so on for all the pages. Does anyone know of a command line utility or script that could help with this? ---------- Output from pdfimages -list -f 1 -l 1 file.pdf: page num type width height color comp bpc enc interp object ID x-ppi y-ppi size ratio -------------------------------------------------------------------------------------------- 1 0 image 1921 1561 rgb 3 8 jpeg no 643 0 200 200 200K 2.3% 1 1 stencil 1 1 - 1 1 image no [inline] 0.692 2 - - 1 2 stencil 1 1 - 1 1 image no [inline] 0.722 0.650 - - 1 3 stencil 1 1 - 1 1 image no [inline] 3 3 - - Second PDF: page num type width height color comp bpc enc interp object ID x-ppi y-ppi size ratio -------------------------------------------------------------------------------------------- 1 0 image 456 625 gray 1 8 jpx yes 251 0 72 72 11.7K 4.2%