I am working on an application that has to be tight control of time flow during a movie recording.
Apple says the iPhone 5 can capture HD video up to 30 fps. If shoot a video and play it on quicktime I see a variable FPS, that reaches 30 fps at some moments, but at the same time quicktime reports the video as being 29.75 fps.
As far as I understand, for each second of video, an integer number of frames should be displayed, not a fractional number. I first thought that could be related to drop frames. Then I decided to design an method to measure drop frames and realized that for every second of video, the iPhone drops from 1 to 4 frames. Also discovered that every time a frame is dropped iPhone simply copies the last frame again to fill the gap. So in theory, dropping a frame would make no difference in the total number of frames a move would have.
So, this is my problem. What this 29.75 fps is telling? How this number is obtained?
It’s not so much that x number of frames are shown per second, but each frame is shown for 1/x seconds. NTSC (the TV standard in US, Japan and others), runs at 29.97fps. So, each frame is shown for a bit more than 3/100ths of a second before the next frame is drawn. So, in your case, each frame is displayed for roughly .0336 of a second before the next one is shown.