There are a number of videos out there but IMO the sufferfest ones offer the best combination of music, humour and fun. They should especially appeal to those of us who are following the Joe Friel advice about power training and hard intervals!
They started out as pure racing videos but 2 recent ones have been done with the Col collective and feature real countryside and are again IMO less aggressive and more audax style.
You can use the videos in 4 ways:
the video plays and you pedal harder or easier on a scale from 1-10, 1 I have never seen and 10 is death in 30 seconds. Fairly hard to gauge and reproducibility is difficult.
The video plays and you monitor your heart rate on a garmin or similar. problem is that Heart rate lags power and so you can get to the end of a 30 second sprint and your Heart rate barely reaches the limit and then peaks 5 seconds into the rest interval
Most turbos and a computer: using either trainerroad or the sufferfest app and an ANT+ USB stick you record your heart rate, cadence and wheel rpm. You have your turbo set at a single specified resistance which has been tested by trainerroad, etc. The computer can then from cadence, rpm and resistance work out virtual power. This changes almost instantaneously and allows very accurate intervals. You change the difficulty of the workout by altering your gears. So for example I knew on my old trainer that recovery intervals at level 2 was small ring and next to largest cog at a cadence of 85-90. FTP was either little ring and 14 cog at 90 or a bit smaller at 100 cadence. A grind at 60rpm would need big ring and so on. Initially there is some hunting around to get the right settings. It is ideal if you can do the hard interval in big ring and recovery in little ring without changing the cassette position as it allows you to transition from recovery to interval very fast.
There are now 5-7 turbos which will talk to the app, either trainerroad or sufferfest. The first was the Wahoo kickr, I think the second was the Tacx Neo and now there are several more. With these the computer tells the turbo to produce 250W. If you pedal at the cadence specified of 90rpm this will be relatively easy (I lie). If however you have a mid interval fail and your cadence drops to 10 then instead of producing 250W/90 power per revolution you are left producing 250/10 power per revolution which can be soul destroying! With this system you generally leave the bike in a single gear and the turbo changes the resistance for you.
I think people vary. I love my new tacx Neo as it is easier to let the power drop with the older system but these turbos cost an arm and a leg. They will measure cadence as well but I found the cadence side poor and added a cadence sensor as well.
I hope this helps