diff --git a/bin/normalize-sweep.sh b/bin/normalize-sweep.sh
index 22c6fa2..c40f550 100755
--- a/bin/normalize-sweep.sh
+++ b/bin/normalize-sweep.sh
@@ -52,10 +52,12 @@ probe() {
   local head; head=$(head -c 2097152 "$f" | grep -aob -m3 -E 'moov|mdat|moof' | tr '\n' ' ')
   if grep -q moof <<<"$head"; then echo "remux fragmented"; return; fi
   # real VFR test: do the gaps between the first ~400 frames vary? (dts is monotonic even with B-frames)
+  # portable awk (Debian's mawk has no asort): deltas -> sort -n -> median + spread
   local vfr; vfr=$(ffprobe -v error -select_streams v:0 -show_entries packet=dts_time -of csv=p=0 -read_intervals '%+#400' "$f" 2>/dev/null |
-    awk 'NF && $1!="N/A" { if (p!="") d[n++]=$1-p; p=$1 }
+    awk 'NF && $1!="N/A" { if (p!="") print $1-p; p=$1 }' | sort -n |
+    awk '{ d[n++]=$1 }
          END { if (n<20) { print "cfr"; exit }
-               for(i=0;i<n;i++) a[i]=d[i]; asort(a); med=a[int(n/2)]; if (med<=0) { print "cfr"; exit }
+               med=d[int(n/2)]; if (med<=0) { print "cfr"; exit }
                bad=0; for(i=0;i<n;i++){ x=d[i]-med; if(x<0)x=-x; if (x > med*0.25) bad++ }
                print (bad > n*0.02) ? "vfr" : "cfr" }')
   [[ $vfr == vfr ]] && { echo "encode vfr"; return; }