What´s the difference between 30p and 30i frame rates (fps) ?

Answer 1

progressive scan is like movie film, it takes the entire frame at once, 30 times per second. interlace scans the frame twice rasing the effective rate to 60 per second. These half frames are called "fields", and using fields reduces transmission bandwidth and image flicker. Interlace was the system always used for analog television. Digital television, computer displays, and DVDs allow for progressive scan.