Virtu/Library/FrameRateCounter.xaml

<UserControl x:Class="Jellyfish.Library.FrameRateCounter" x:Name="frameRateControl"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <TextBlock FontFamily="Consolas" FontSize="12" Foreground="White">
        <TextBlock.Text>
            <Binding Path="FrameRate" ElementName="frameRateControl" StringFormat="{}{0:D} fps"/>
        </TextBlock.Text>
    </TextBlock>
</UserControl>