APM not rewriting properly

As far as i know, nothing is rewritten per default from the backend.

The cleanest solution would now be that the backend code is changed to something like

document.VXReplay.WaveFileName = "http://" + window.location.hostname + strURL;

If for some reason its not possible to change the backend code or the configuration accordingly, your only chance is to modify the response-stream directly through an iRule.

Wouldnt it be sufficient to just rewrite the http://internalservername:8080 with the current hostname?

So some iRule like this:

 when HTTP_REQUEST {
   Don't allow data to be chunked so we can correctly
   replace payload below
  if { [HTTP::version] eq "1.1" } {
      if { [HTTP::header is_keepalive] } {
         HTTP::header replace "Connection" "Keep-Alive"
      }
      HTTP::version "1.0"
  }

   save host
  set hostname [HTTP::host]
}

when HTTP_RESPONSE {
     collect response data
    if { [HTTP::header exists "Content-Length"] } {
       set content_length [HTTP::header "Content-Length"]
    } else {
       set content_length 4294967295
    }
    if { $content_length > 0 } {
       HTTP::collect $content_length
    }
}

when HTTP_RESPONSE_DATA {
  if { $::patch_apple_and_banana } {
    set find "http://internalservername:8080"
    set replace "https://$hostname"
    set offset 0
    set diff [expr [string length $replace] - [string length $find]]

     Get indices of all instances of find string in the payload
    set indices [regexp -all -inline -indices $find [HTTP::payload]]  
    foreach idx $indices {
      set start [expr [lindex $idx 0] + $offset]
      set end [expr [lindex $idx 1] + $offset]
      set len [expr {$end - $start + 1}]

       replace the instance of find with the contents of replace
      HTTP::payload replace $start $len $replace

       modify offset if the replace string is larger or smaller
       than find.
      incr offset $diff
    }
  }
}

(based on this site)

Though i'm not sure if you really should inspect any response that's coming through; But i guess you get the point.