def __set_prop(self, prop, value):
        assert self.source

        if self.__source_uses_keyframes():
            try:
                position = self._project.pipeline.get_position()
                start = self.source.props.start
                in_point = self.source.props.in_point
                duration = self.source.props.duration
                if position < start or position > start + duration:
                    return
                source_position = position - start + in_point

                with self.app.action_log.started(
                        "Transformation property change",
                        finalizing_action=CommitTimelineFinalizingAction(self._project.pipeline),
                        toplevel=True):
                    self.__control_bindings[prop].props.control_source.set(source_position, value)
            except PipelineError:
                self.warning("Could not get pipeline position")
                return
        else:
            with self.app.action_log.started("Transformation property change",
                                             finalizing_action=CommitTimelineFinalizingAction(self._project.pipeline),
                                             toplevel=True):
                self.source.set_child_property(prop, value)