diff --git a/openbsc/contrib/rtp/rtp_replay.st b/openbsc/contrib/rtp/rtp_replay.st
index 7fa9a4c9d..e26d07388 100644
--- a/openbsc/contrib/rtp/rtp_replay.st
+++ b/openbsc/contrib/rtp/rtp_replay.st
@@ -7,11 +7,15 @@ FileStream fileIn: 'rtp_replay_shared.st'.
 
 
 Eval [
-    | replay |
+    | replay file host dport |
 
+    file := Smalltalk arguments at: 1 ifAbsent: [ 'rtpstream.state' ].
+    host := Smalltalk arguments at: 2 ifAbsent: [ '127.0.0.1' ].
+    dport := (Smalltalk arguments at: 3 ifAbsent: [ '4000' ]) asInteger.
+    sport := (Smalltalk arguments at: 4 ifAbsent: [ '0' ]) asInteger.
 
-    replay := RTPReplay on: Smalltalk arguments first.
+    replay := RTPReplay on: file fromPort: sport.
 
     Transcript nextPutAll: 'Going to stream now'; nl.
-    replay streamAudio: '127.0.0.1' port: 4000.
+    replay streamAudio: host port: dport.
 ]
diff --git a/openbsc/contrib/rtp/rtp_replay_shared.st b/openbsc/contrib/rtp/rtp_replay_shared.st
index dd32aed7a..7b68c0f5e 100644
--- a/openbsc/contrib/rtp/rtp_replay_shared.st
+++ b/openbsc/contrib/rtp/rtp_replay_shared.st
@@ -42,8 +42,18 @@ Object subclass: RTPReplay [
             file: aFile; yourself
     ]
 
+    RTPReplay class >> on: aFile fromPort: aPort [
+        ^ self new
+            initialize: aPort;
+            file: aFile; yourself
+    ]
+
     initialize [
-        socket := Sockets.DatagramSocket new.
+        self initialize: 0.
+    ]
+
+    initialize: aPort [
+        socket := Sockets.DatagramSocket local: '0.0.0.0' port: aPort.
     ]
 
     file: aFile [ 
@@ -59,7 +69,7 @@ Object subclass: RTPReplay [
 
         last_time := nil.
         last_image := nil.
-        file := FileStream open: filename.
+        file := FileStream open: filename mode: #read.
 
         "Send the payload"
         dest := Sockets.SocketAddress byName: aHost.