mine got worse when hot.. head was warped. leakdown test will rule out allot but yes you have one cylder failing. take out the new plugs and see which one looks different. have you done a compression test?
oh there plenty out there like any tutorial search, i find some are excellent most are obvious stuff and some are bad. looking for people specifically to watch, like a series which is really on point and worth saving.
i know mine only records when it has power which is when the car is on. you could hardwire it to run 24/7 but your would just record over everything in a short period of time. i thin ksome more pricey ones can record after a gforce sensor triggers and runs from battery for a short time.