Re: [Avid-L2] 29.97 and HD / RANT

Sorry for my long rant, but as a finishing editor and colorist, frame rates are at the core of my work… and I believe is the essence of moving images, the illusion of movement… needless to say!

I have worked on projects for both broadcast television and movie theater release in Europe and the USA mostly, and consistent frame rates is critical in any post-production workflow, which usually is defined by the main delivery market. Especially today, with the numerous digital cameras which allow you to shoot in your preferred frame rate, from interval timer (ie 1 frame every 30sec for timelapse) to high speed frame rate (ie Phantom camera at 1.600fps), all of these will have to be conformed for creative and delivery specs requirement.

I think it is important to differentiate frame rates for acquisition and delivery. More and more digital professional cameras allow you to select frame rates up to 220fps (see the recent release of the BMD Ursa Mini Pro 12K). From wanting to get slow motion footage, timelapse, film look or special purposes for visual FX, I believe they are a lot of good reasons not to stick to delivery frame rates when filming.

For delivery, I believe most of us are concerned with international standards for the targeted markets. ITU, EBU and SMPTE are the main organisations working on these standards. Some of us who worked with video analog standard definition, we had to follow BT.601 standard for a long time. For HD broadcast delivery, until now we had to follow BT.709 standard  if we wanted to have our show accepted with most networks. For UHD 4K delivery (mostly streaming services) the actual standard is defined with BT. 2100 (an extension from BT.2020) which also specifies specs for SDR and HDR.

I agree with Mark, productions need to make sure all the players from shooting to delivery talk about the same numbers. And there is a reason for these numbers, that we like it or not!😉

In the 80s/90s when software were developed to help transition from film/analog video to digital in the USA, many software companies with no video experience, started using some rounding numbers for coding frame rates (30fps (instead of 30/1.001), or 24fps, or 23.98fps (instead of 24/1.001) which had a negative impact on how the video was interpreted in real production when digitized.

I hope the historian/engineer among us won't give me grief for my short summary. For the USA, the TV NTSC color encoded system devised in the late 1930s had to make sure video and audio frequency signals did not interfere with each others when transmitted (ie audio creating a visual pattern). Hence the engineers decided to adjust the video carrier by a factor of 0.1% to avoid intermodulation between video and audio signals. The NTSC frame rate was created: 30fps/1.001 = 29.97002997fps (accepted round up to 29.97fps)

Because of film conversion to US television system, 24fps frame rate had to be adjusted the same way: 24fps/1.001 = 23.976023976fps (accepted round up to 23.976fps)

When shooting it is important that all devices work with all the same frame rates including audio, video, external recorders… otherwise out of sync issues will raise. Same for post. You don't want your Protools audio mixer working in 24fps when you edited @ 23.976fps!

With 29.97fps frame rate, drop frames still need to be apply for long form in order to get accurate timecode (in post, a frame is a frame, but we still need to accommodate the NTSC standard for transmission)

For a long time USA television sets could only playback a 29.97fps interlaced signal. Any 23.976fps had to be converted to 29.97fps using a the 3:2 pulldown techniques. At some point, most DVD and Blu-ray players were able to convert on the fly 23.976fps to 29.97fps to accommodate television displays. I tried to match the master movie frame rates as much as possible when authoring disks from that time on.

Regarding digital theater projection, today we are dealing with 2 main digital cinema package (DCP) standards: Interop and SMPTE. Interop is the original standard before SMPTE came up with a new standard. Interop only accept 24fps. SMPTE DCP accepts 24, 25, 30, 48, 50 & 60fps @ 2K

Today I see no reasons for shooting interlaced video when you have a choice. Most broadcasters, if they have to transmit interlaced video signal, will convert progressive to interlaced with no problem (or they shouldn't). If the network requires an interlaced master (ie 59.94i), I would still recommend production to create a progressive master and then make your interlaced deliverable.

My 2 cents,

David Baud

Colorist & Finishing Editor

david at kosmos-productions.com

On Aug 3, 2020, at 8:02 PM, Mark Spano <cutandcover@gmail.com> wrote:

Neither 24.00hz or 30.00hz exists in video. 

Please don't spread this. It's false. It might have been true at some point long before the HD days, but I guarantee you can have all of the following frame rates in video without blinking.

23.976

24.0

25.0

29.97

30.0

59.94

60.0

And many more!

 

On Mon, Aug 3, 2020 at 9:54 PM hoplist <hoplist@hillmanncarr.com> wrote:

Very interesting, and in hindsight, it's obvious why I am wrong about 24 versus 25. The world has changed since I last dealt with international shooting. It makes perfect sense to me that in 50hz countries, people shoot at 25fps for domestic consumption. But I do have a question. If I were shooting for international distribution, should I consider 25fps instead of 24fps? Or are we still shooting 24fps for international?

Now let me deal with my 24 vs. 23.976 and 30 versus 29.97 pet peeve. Outside of an engineering context, the distinction has no meaning. It's merely a display of technical prowess, like quoting pi to six digits instead of 2 just because you can. You don't need to say 23.976 because, if you are talking about video, we all know that's what you mean. In video 24fps is 23.976hz. 30fps is 29.97hz. Neither 24.00hz or 30.00hz exists in video. If you set your DSLR or your iPhone to "30fps," you've set it to 29.97hz. Sure, you can shoot film at 24.00hz and 30.00hz, but when you convert your film to video, it will be 23.976hz or 59.94hz when you are done and no one will know the difference. 

By the way, if you are shooting 24.00hz in film, why?

Cheers,

                 tod

On Aug 2, 2020, at 1:03 AM, luca_gazzolo via groups.io <luca_gazzolo=yahoo.com@groups.io> wrote:

Tod, despite the historic american hegemony, more people shoot at 25 fps than 24 (I assume You mean 23.976) or 30 fps, simply because the majority of the countries in the world are on 50 hertz power rather than 60. While I do not mind shortening 29.976 as 30 fps, I think that 23.976 fps should be referred to as such, or shortened as 23.98, to avoid confusion with true 24 fps, as shot outside the US.

Regards, Luca