<Grid>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="2*"/>
                        <RowDefinition Height="3*" x:Name="bottomRow"/>
                    </Grid.RowDefinitions>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="*"/>
                        <ColumnDefinition Width="250"/>
                    </Grid.ColumnDefinitions>

                    <Grid Width="{Binding ActualHeight, ElementName=bottomRow, Mode=OneWay}" Name="CameraGrid" Margin="20" Grid.Row="1" Grid.Column="0" Background="Green">

                    </Grid>
                </Grid>

<Grid Name="CameraGrid" Margin="20" Grid.Row="1" Grid.Column="0" >
    <Grid Width="{Binding ActualHeight, Mode=OneWay, RelativeSource={RelativeSource Self}}" Background="Green">

    </Grid>
</Grid>