pitch shifting video rate math in cents

Question

Sorry for my poor math/music knowledge.. Assumed whe want to play a video file at 50% and at 75 % speed how much cent do I have to shift in both situation to keep the same pitch and what would be the formula?

Thanks in advance!!

Answer 1

reducing the frequency by 50% means the sound is one octave lower

one octave is 12 halve-tones

1 halve tone is 100 cents

so if you play it at 50% you need to pitch it up by 1200 cent