Origins of the 405 line system.

[ppppenguin]

Flyback time with a CRT will always be a compromise. The pioneers had to find out what worked by a mixture of theory and experiment. Electrostatic CRTs can do flyback very swiftly without expending much power. Magnetic deflection can't. There's that old V = 0.5 * L^2 at work to stop you. As for why magnetic deflection became universal that's easy to answer. If you want wider deflection angles and hence shorter CRTs then the deflection plate geometry becomes impossible very quickly. The beam just hits the plates. Perhaps even more important is when you increase the EHT to get higher brightness the ES deflection voltage increases linearly with EHT while the current for EM scanning only goes up as the square root of EHT. For small 'scope tubes they developed PDA (Post Deflection Acceleration) but I doubt that was feasible for big CRTs.

Coming right up to date with the assortment of HD standards the 1.5GHz serial digital interface can carry about 15 different formats. From 1080/60i and 1080/30p right down to to 720/24p. The last of these has H blanking several times longer than active line.