diff --git a/tools/motionblur.sh b/tools/motionblur.sh
index ab47916..3f7823b 100755
--- a/tools/motionblur.sh
+++ b/tools/motionblur.sh
@@ -11,6 +11,13 @@
 
 set -e   ;   set -u
 source tools/config.sh
+source tools/fonctions.sh
+
+START=50
+if [ $# == 1 ]
+then
+	START=$1
+fi
 
 NB_SRC=$(ls -1 frames/Spool | wc -l)
 
@@ -19,7 +26,7 @@ printf "%s: %d frames\n" $0 $NB_SRC | tee -a WS/log
 # -------------------------------------------------------
 #		MAIN LOOP
 
-for frame in $(seq 1 $(( $NB_SRC-1 )) )
+for frame in $(seq $START $(( $NB_SRC-1 )) )
 do
 	imgA=$(printf "frames/Spool/%05d.png" $frame)
 	imgB=$(printf "frames/Spool/%05d.png" $((frame-1)))