fps vs. fps

[Larry Asbell]

Darn good question, I too have been bewildered that people trying to be so precise can casually mix up frames per second and fields per second when things are confusing enough already! I asked the same question as you at an HD seminar and got a partially satisfying answer that progressive formats are described in frames per second while interlaced formats are (sometimes) described in fields per second. Personally I see no reason to use different yardsticks, but I’d like to hear what others have to say. Anyway thanks alot for asking this question.

[John Foley]

Frames per second and fields per second are only relevant when using interlaced video.

One might understand that once the frames per second is locked, fields per second is 2x that. DV, SD are two standard interlaced (NTSC) formats. While they are 29.97 frames per second, they really have 30 fields per second because the timecode generated for Drop Frame is missing some counts to virtually lessen the playout time.

In HD land we have mostly progressive frames of video 24 Frames per second with 24 fields. Except for 1080i which is again interlaced but Non Drop Frame 30 Frames per second but 60 fields per second

Most assuredly can be confusing cause this is the grand USA (ATSC)

Please visit http://www.thefinalcutstore.com for all your Final Cut needs.

[Graeme Nattress]

I’m sorry, but do you have any idea what you’re talking about?

29.97fps is exactly that – it runs at 29.97, or more accurately 30 * 1000 / 1001 frames per second, the field rate for interlaced video at that speed is 59.94 fields per second.

Drop frame timecode misses some numbers (doesn’t drop frames, doesn’t play at a different speed than 29.97fps) so that the timings of a clip of video match real world time as timecode cannot otherwise cope with the fractional NTSC framerate of 29.97fps. Remember, timecode, drop frame or otherwise is just a counting scheme.

When you have 24 frames per second, you don’t have any fields at all. You have progressive frames or interlaced fields, not both. (actually, you often have progressive video encoded as interlaced to make it compatible with tape formats designed for interlace and broadcast designed for interlace, but essentially, you either have frames or fields). And when you do have 24 frames a second, more often than not, it’s actually 23.98fps or again, more accurately 24 * 1000 / 1001 frames per second.

https://www.kenstone.net/fcp_homepage/24p_in_FCP_nattress.html explains things in more depth.

The “NTSC” fractional frame rate came about in their transition from black and white to color television, and the need for backwards compatibility. To do this they added color as a subcarrier to the same luma signal that is used for black and white, but the frequency of this beat with the audio subcarrier, so they moved the video frame rate ever so slightly, by the fraction 1000/1001, thus causing no end of problems for the video editor and engineer for many years to come.

– http://www.nattress.com – Film Effects and Standards Conversion for FCP

[Gary Adcock]

[mortimer heathcliff] “something i’ve noticed in the FCP presets. i’m doing a project at DVCPro HD (1080i/60), and have always been a little curious at the “60” vs. “29.97” or “30” nomenclature.””

To add to Graeme’s info..

you can thank Sony for not allowing use to join the future on this subject,even though most people accept that HD delivery is at 60 frame or 60 fields.

Rather than “confuse” people coming to HD production Sony insisted on maintaining the SD convention of using “frame” rate as opposed to what everyone else is doing, as most people understand that 1080 is mostly “i” and 720 is always p for DELIVERY over the air.

< there is not a standard to deliver 1080 24psf to the home - that is an acquisition format -- and that 24sf plays back at 48i to match the rest of the Sony formats>

gary adcock
Studio37
HD & Film Consultation
Post and Production Workflows