<Grid>

        <Border BorderThickness="" BorderBrush="#3c4d72"

                 CornerRadius="" Background="LightBlue"  Width="" Height="" >

            <MediaElement Name="mainMediaElement"   Volume=""

                       Stretch="Fill"  Width="" Height=""  >

                <MediaElement.Clip>

                    <!--矩形裁剪-->

                    <RectangleGeometry RadiusX="" RadiusY=""

                                       Rect="0,0,600,350" />

                </MediaElement.Clip>

                <MediaElement.Triggers>

                    <EventTrigger RoutedEvent="MediaElement.Loaded">

                        <EventTrigger.Actions>

                            <BeginStoryboard>

                                <Storyboard>

                                    <MediaTimeline Storyboard.TargetName="mainMediaElement"

                                                 Source="font/TestMedia.mp4"  RepeatBehavior="Forever" />

                                </Storyboard>

                            </BeginStoryboard>

                        </EventTrigger.Actions>

                    </EventTrigger>

                </MediaElement.Triggers>

            </MediaElement>

        </Border>

    </Grid>