How to add looping graphic / progress indicator / lap marker?

[samth]

Perhaps this suits your requirements:

Progress Bar for Video? (Instagram Style)

Since the bulk of the replies were posted before the introduction of keyframes, there is now an easier solution available: Add a video track, which is on top of every other track. Either insert an image or a colour (Open other > Colour) into the track. Use the “Size and Position” filter with “Distort” checked to achieve the right shape. Set the playhead on the desired end time and press on the clock/timer button to enable advanced keyframes. A keyframe will be generated at this position (Visib…

You can match the bar exactly to the clip.
To loop the bar, you could just copy the clip that represents the progress bar as many times as needed.
You could also use an image editing software like GIMP to create a rectangle outline with a transparent background. Export it as a PNG and insert it into a higher track. Now, you fit the bar into the outline. This represents the whole duration of the clip. I can provide detailed instructions if you need them.