How do I take a video of the ILDA test pattern?

I have an iPhone and I am trying to photograph or take a video of my laser displaying the ILDA test pattern so the pros here can analyze it. If I take a photo, it only captures what was being scanned at the moment the picture was being taken, and if I try to do a video, the flicker is a lot worse in the video than in real life. Back in the day, I would use 100 speed film and keep the shutter open for longer. Can I do this on an iPhone electronically?

There are probably apps that can do this but even then, I think it just overlaps video frames. Also, for any kind of long exposure, you're going to need a tripod. For static images, I use a dSLR and set my exposure to 1/15".

I don't use iPhone but here is something that *might* help. https://www.usatoday.com/story/tech/...one/858794001/. Again, not sure if that is a true long exposure or just stacked video frames.

Thanks for the link! I will try that tomorrow. Live photos take a small burst of pictures and I guess you can stitch them together in one frame is you use the "long exposure" option. Brilliant!