Japan, Germany, France, China, and the UK check their tracks at high speed. I don't know if Spain does, but there are news articles about them ordering such an inspection train in 2019: https://www.railjournal.com/infrastructure/adif-orders-high-...

https://de.wikipedia.org/wiki/RAILab

https://en.wikipedia.org/wiki/Doctor_Yellow

https://en.wikipedia.org/wiki/SNCF_TGV_Iris_320

https://en.wikipedia.org/wiki/China_railways_CIT_trains

https://en.wikipedia.org/wiki/New_Measurement_Train

The camera would probably only need to look at a very small section at high speed. They could be specifically made to film the tracks or the wheels of the train. Such cameras exist. Not cheap, but even some YouTubers have similar ones, to film high speed impact videos of things going much faster than trains. Might be worth it for trains.

Not necessarily, no. Train underframes can be quite crowded and this equipment is very industrial.