diff -urNp pitivi-0.13.5.old/pitivi/factories/base.py pitivi-0.13.5/pitivi/factories/base.py
--- pitivi-0.13.5.old/pitivi/factories/base.py	2011-01-30 16:40:27.672000221 +0530
+++ pitivi-0.13.5/pitivi/factories/base.py	2011-01-30 16:41:12.784000223 +0530
@@ -421,7 +421,11 @@ class SourceFactory(ObjectFactory):
                 b.csp = gst.element_factory_make("identity")
 
             b.alpha = gst.element_factory_make("alpha", "internal-alpha")
-            b.alpha.props.prefer_passthrough = True
+            try:
+                b.alpha.props.prefer_passthrough = True
+            except AttributeError:
+                self.warning("User has old version of alpha. "
+                        "prefer-passthrough not enabled")
             b.scale = gst.element_factory_make("videoscale")
             try:
                 b.scale.props.add_borders = True