Questions on framerates in film

Author: Adamwankenobi
Time: 28-Sep-2005 7:06 PM
Post link

This is for the video experts: Why are films shot at 24 fps? Also, how do you convert 29.970 fps video to that framerate, while keeping all audio in sync with the video?

Author: GundarkHunter
Time: 29-Sep-2005 11:37 AM
Post link

Films have been shot @ 24fps since the beginning of the sound era. It may have had something to do with Vitaphone synce issues, but I think it was that engineers found they got the best sound quality (of the time) at that frame rate.

Video transfers are done in North America according to a 3:2 ratio. That is, one frame is recorded for 3 fields, and the next is recorded for 2, with contiunuing alternation, resulting in a frame rate of 29.97fps with no noticeable flicker. Prior to DVD, this used to result in some goofy-looking artifacts, but they were only visible in slow-motion. You would have fields interlace that weren't supposed to, and the frame would jitter. DVD has a flagging system built in so that progressive scan displays 'drop' the redundant field. Some problem DVDs have crept through the system, but most are true to what I have said. 3:2 pulldown has its quirks, but generally works well, and is infitely preferable to PAL speedup.

Princess Leia: I happen to like nice men.
Han Solo: I'm a nice man.

Author: GundarkHunter
Time: 29-Sep-2005 11:39 AM
Post link

I think I misunderstood your question. If you're converting the other way (video to film) I'm not sure how it works. I know that some companies do specialty 24fps video rigs for the film iundustry, but have no idea how exactly they work.

Princess Leia: I happen to like nice men.
Han Solo: I'm a nice man.