--- a/trunk/tubetutor/ffmpeg.py
+++ b/trunk/tubetutor/ffmpeg.py
@@ -20,8 +20,10 @@
 
 if platform.system() == "Linux":
     grabber="-video_size 1920x1080 -f x11grab -framerate 20 -i :0.0 -f pulse -i 1"
+    audio=True
 else:
     grabber="-f gdigrab -framerate 20 -i desktop"
+    audio=False
 
 #
 # The following helper functions will retrieve the pathnames for the ffmpeg tools
@@ -200,12 +202,15 @@
         start(filename, params)
         wait()
 
-    def mux(self, filename, audiofile):
+    def mux(self, filename, audiofile, replace=False):
         print("*** mux(%s, %s)" % (filename, audiofile))
         duration = video_duration(self.lastfilename)
         params = " -i %s -i %s -y" % (self.lastfilename, audiofile)
         params += " -t %d" % (int(duration)+1)
-        params += " -filter_complex \"[0:a][1:a]amerge,afade=out:st=%f:d=3\"" % (duration-3.0)
+        if replace:
+            params += " -af \"afade=out:st=%f:d=3\"" % (duration-3.0)
+        else:
+            params += " -filter_complex \"[0:a][1:a]amerge,afade=out:st=%f:d=3\"" % (duration-3.0)
         params += " -map 0:v:0 -map 1:a:0"
         params += self.qfilter
         self.lastfilename = filename