I’ve run into this issue so many times, practically on a weekly basis, so once and for all, 1080i / 60i is NOT 60fps. That is 60 frames per second. Never was, never will be, it’s just not going to happen. Let’s take a look shall we?
First off, the “i” in the number. 1080i / 60. The “i” stands for Interlaced.
With 720p or 1080p the “p” stands for Progressive.
Those two letters make all the difference in the world and that letter “i” is why 1080i / 60 is not 60 frames per second.
A progressive format is made up of a series of full frames. Each Frame is a single image that covers the entire screen. For example, the following is a single Frame of Progressive Video.
There’s the entire image in one frame, it’s not a split image as you will see shortly. So when you see a Progressive frame rate, the second number refers to the amount of FRAMES it takes to make up one second of video. 720p / 60 for example means there are 60 frames for every second of video. 60 images like the one above make up one full second of video.
An interlaced format is made up of two fields per frame of video. Each field is half of the single image. When combined, the two fields make up one frame of video that covers the entire screen. For example, here is the first field of of a single frame of video.
So 1080i / 60 stands for 60 FIELDS per second, divide by 2 gives us 30 FRAMES per second, or as we all know in drop frame timecode, 29.97 FRAMES per second.
Therefore, 1080i / 60 has a framerate of 29.97.
Why is it called 1080i / 60? I have ABSOLUTELY NO IDEA. If anyone has the name and / or phone number of the engineer and / or marketing / sales person at the camera company who coined that format, please pass it along as I would LOVE to have a little chat with them. Calling the format 1080 / 60i has only created confusion where there shouldn’t be any.
I hope this clears everything up.