60p and ProRes 422?

[Oliver Peters]

Here’s some reading that might help get you up to speed.

https://digitalfilms.wordpress.com/2009/04/16/what’s-wrong-with-this-picture/

https://digitalfilms.wordpress.com/2003/12/18/a-different-drummer-–-understanding-frame-rates-and-timecode/

Let me try to quickly answer your questions. However, it won’t be short. ☺

Video can be interlaced scan (“i”) or progressive scan (“p”), which goes back to how the image is displayed on a TV or monitor. Older CRT-based TV sets were interlaced, but modern flat panels are progressive. Broadcast SD TV transmission was interlaced, but broadcast HD transmission is both interlaced and/or progressive, depending on the standard used.

In broadcast displays and TVs, the image is display in scanlines. Interlaced divides the whole frame into 2 fields, where each field has half of the scan lines that are typically offset in time. The scanlines alternate vertically between field 1 and field 2. So in NTSC, you have 60 fields/30 interlaced frames within a second, with motion accuracy of 1/60th of a second.

A progressive frame contains the complete information for that frame. In NTSC there are 30 progressive frames with motion accuracy of 1/30th of a second. “FPS” can stand for “fields per second” or “frames per second” depending on the context. The one exception to all of this is the 720p HD standard where frame size is 1280 x 720 and frame rate is 60 progressive frames per second. No broadcast transmission goes higher, so there is no 120fps in broadcast or streaming services (yet).

It is not 23.94, but rather 23.976 – also abbreviated to 23.98. Both are rounded values for a much longer decimal number. True 24fps is generally denoted as 24.0 these days and usually that only applies to true film acquisition and theatrical projection. Because the NTSC TV frequency syncs to 59.94Hz and not to 60Hz, video production uses an offset rate. 29.97 instead of a true 30 and 23.976 instead of a true 24.0.

Film capture is inherently progressive. When all TV transmission was interlaced, 24.0 “progressive” film was transferred at a slightly slower rate (23.976) and converted to 29.97i (60 field per second) using a method called 3:2 pulldown. Once HD and more modern flat panels became the norm, it was possible to work in and display true 23.976p content and to deliver masters and distribution copies in this standard. So we were able to dump the whole interlaced and pulldown methodology.

The PAL color standard was developed later than NTSC and could learn from some of the issues. PAL standards are 25fps (50 fields/25 interlaced frames or 25 progressive frames), synced to a frequency of 50Hz. So 24.0 film was transferred faster at 25fps or PAL used its own particular version of pulldown.

So 23.976, 24.0, 25.0, 29.97, 30.0, 59.94, and 60.0 are all completely different and distinct frame rates. When you mix these standards something is invariably done to the footage to conform it to your base or timeline format. Frames may be repeated or the footage slowed or sped up depending what the source and target rates are and what process you are applying.

Most professional production cameras do not shoot at 120fps with the intent of that being the playback rate. Generally it’s used for slow motion effects. You shoot at 120, but play/edit/deliver at 23.976. Same as shooting high frame rates on film. That sort of thing.

If you are delivering to YouTube, generally upload an H.264 or H.265 codec wrapped in a .mov or .mp4 container.

I hope that all of this helps clear things up.

– Oliver

Oliver Peters – oliverpeters.com