The approach is fundamentally bad. You're using split, but you don't have a separated list of things to split on.

Either option you choose, you need to

  1. Parse the HTML
  2. Locate the elements
  3. Modify the elements
  4. Regenerate the HTML

In this case, that can all be done by one substitution. 

s/
   (<iframe
   [ ]title="YouTube[ ]video[ ]player"
   [ ]width=")([0-9]+)("
   [ ]height=")([0-9]+)("
   )
/
   $1 . "320" . $3 . ( (320/$2)*$4 ) . $5
/xeg

[download]

In reply to Re^3: Grabbing url from iframe by ikegami
in thread Grabbing url from iframe by htmanning

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