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DF vs NDF

Published : 11th July 2004


>I'm from the school (not necessarily the correct school) of you shoot DF >if you are doing TV broadcast and NDF is you are doing all else.

This is a great topic for a new thread!

My understanding is that DF is only necessary if your recorded program is going to exceed 30 mins. in length and it's going to be broadcast because broadcast needs to be time specific and it's critical for post to know exactly how long the recorded material is. Right around 30 mins is where the time starts to drift from actual time in NDF mode.

I've also heard that this is less of an issue with non-linear edit systems.

Of course, this is all "my understanding" which should be taken with a grain of salt.

Anyone care to support/clarify?

Dan Coplan
Cinematographer/Editor/DVD Authoring
www.dancoplan.com



Dan Coplan writes:

>Right around 30 mins. is where the time starts to drift from actual time >in NDF mode.

Huh? The difference is progressive, so you're a percentage off after a single second and it continues from there. You might not notice it much, but it's always there.

I've always understood it as DF for news gathering, as that is handled very quickly and accurate time is very important, and NDF for long-form work such as docs.

Mitch Gross
NYC DP



>Huh? The difference is progressive, so you're a percentage off after a >single second and it continues from there. You might not notice it much, >but it's always there.

My mistake. What I meant to say was not that the timecode doesn't drift until you hit 30 mins. (the time is recorded differently after the first minute*), but that it doesn't become a significant issue until you hit that 30 min. mark. This is something I heard, not something I preach so I was looking for clarification on this issue myself.

In fact, at the 30 min. mark, a program recorded in NDF is approximately 2 seconds shorter than the timecode it displays.

*DF numbering scheme - For every minute that passes, :00 and :01 are skipped except for minutes ending in 0 (00, 10, 20, etc.)

Dan "Confusing Myself" Coplan
Cinematographer/Editor/DVD Authoring



>In fact, at the 30 min. mark, a program recorded in NDF is >approximately 2 seconds shorter than the timecode it displays.

I think you meant longer.

Mitch Gross
NYC DP



No, I meant shorter.

The signal is recorded at 29.97, a smidge less than how we count comparable clock time which would be 30. As an example, 100 seconds = 3000 frames, clock time, but 100 seconds = 2997 frames NDF time, therefore in NDF, the recorded material (starting after one minute) is less than what the timecode indicates.

Dan Coplan
Cinematographer/Editor/DVD Authoring



Well, it takes an old fart like me who saw it all happen, to teach you DF vs. NDF...

Way back when B&W TV was invented, TV signals in North America were broadcast at 60 interlaced scans per second to create 30 complete frames per second. This was very convenient because the transmitters and home receivers could use the available 60 cycle AC power to keep everything in sync. Then along came colour (or color) as the Yankees call it. It was then discovered that a 30 fps color picture when received on a B&W set had an annoying hummm.

So the politicians of the day, being politicians, and not wanting to offend their aged voters by telling them to chuck their old B&W sets and buy colour, decreed that the new color signals had to be broadcast in such a way that grandpa could see a B&W picture of a young Johnny Carson on his 12 inch TV set with the round picture tube. So came into being the FCC law that color programs would have to be broadcast at 29.97 frames per sec. which eliminated the audio hummm. We have been burdened with the immense consequences of this stupidity ever since.

For example a one hour production recorded at 30 fps would contain 30(frames) x 60(seconds) x 60(minutes) or 108,000 frames. The problem was that if this tape was broadcast at just 29.97 fps, at the end of the hour only 107,892 of the 108,000 frames would have been broadcast - with the last 108 frames or 3.6 seconds never seeing the light of day. While missing the last 3.6 seconds of credits would not have been the end of the world, the points at which commercials and station breaks were to be inserted would be a mess because they would be out of sync from anywhere from 0 to 3.6 seconds depending where in the hour show they were placed.

The solution was to skip certain frame numbers (NOT TO DELETE OR DROP THE ACTUAL FRAMES) so at the end of the hour as the 107,892nd frame was being broadcast, the time code would read exactly one hour, zero minutes, zero seconds and zero frames. (01:00:00:00), and if in editing, you fast forwarded the tape to the 15 min. or 30 min. point as shown by the time code, then you would have reached the 15 min. or 30 min. point in the show that the real broadcast would be at as seen by grandpa on his B&W set and by the affiliate stations who were inserting local commercials at these points.

The exact formula as to which frame numbers (not actual picture frames) to drop so you would end up with a 107,892 frame tape that would last a full broadcast hour is as follows :

Two frame numbers - "00" and "01" - are dropped every minute ( 2 x 60 = 120 frame numbers ) EXCEPT for
minute points that have a "0" number - 00, 10, 20, 30, 40 and 50 minutes - ( 2 x 6 = 12 frames). This results in 120-12 or 108 frame numbers (not frames) being skipped.

Hope you all got it now...

Robert Rouveroy csc
The Hague, Holland

I plan to live forever. So far, so good.



Dan Coplan writes :

>No, I meant shorter. The signal is recorded at 29.97, a smidge less >than how we count comparable clock time which would be 30. As an >example, 100 seconds = 3000 frames, clock time, but 100 seconds = >2997 frames NDF time.

Yes but we deal in frames, and 3000 frames (actually 2 fields per frame) of NTSC is longer than 100 seconds, which is where all the confusion comes from.

Should have been called skip number

Steven Gladstone
Cinematographer
Gladstone Films
Brooklyn, N.Y. U.S.A.
East Coast List administrator - Cinematography Mailing list



Robert --

Thanks for the history lesson for those who did not know. Clear and concise. But I think the original question is geared towards the settings on a video camera. In which situations should one use timecode in drop frame mode and in which situations in non-drop frame mode?

I say news gathering gets drop frame because the material is often handled quickly and they need accurate running times. Longform doc. work and certainly any film transfers that are meant for EDL's that will have a film matchback should use non-drop for simple clarity in the numbers.

Mitch Gross
NYC DP



Mitch Gross wrote :

>I say news gathering gets drop frame because the material is often >handled quickly and they need accurate running times. Longform doc. >work and certainly any film transfers that are meant for EDL's that will >have a film matchback should use non-drop for simple clarity in the >numbers.

That's a pretty good way of looking at it. I would add that anything destined for broadcast must be in drop frame. That's both for real time accuracy and the fact that the broadcasters require it. Note that in terms of television series, this does not mean that post production is in drop frame, for a number of reasons. Primary is the simple fact that most series production (whether film or HD tape) is done at 24fps. Editing systems that can cut at 24 frames (Avids, Final Cut systems properly equipped for capture and output) operate under the assumption that all "A" frames fall on time codes ending in 0 or 5 - but this assumption can only be made if the time code is non-drop frame.

In the case of NTSC finishing, a drop frame recording can be made for network delivery after post production is complete. In the case of HD finishing, there is no drop frame mode for 24p, so once again, network delivery elements are made with drop frame, but the masters are not.

Mike Most
VFX Supervisor
IATSE Local 600
Los Angeles



Many thanks to our Dutch friend Robert Rouveroy csc for that explanation concerning DF vs. NDF in timecode world.

So I have been kind of right all theses years to shoot DF for broadcast and NDF for non broadcast and I'm assuming, filmout video.

Which brings the thread full circle since I mentioned a week or so ago that when you switch the DVX100 to progressive and you were shooting 60i DF, the timecode will default to NDF.

I'm not sure if you can menu set back to DF because my brand new DVX is in Elgin, IL because the machine doesn't like our southern humidity, I guess.

Thanks Mr. Robert!

Allen S. Facemire
DP/Director
SaltRun Productions,inc.
Atlanta
www.saltrunproductions.com



Mitch Gross says :

>I say news gathering gets drop frame because the material is often >handled quickly and they need accurate running times......

I would say that while some of us still shoot network news and magazine pieces, I’m doing a 22:30 TV show every week which I supply DV and Beta originals with DF TC but my editor is changing everything to NDF. We then supply SP masters to Turner who in turn bump them over or up to Digi Beta for air.

I’m wondering what TC format they’re using?

I guess since we’re in our 3rd season I should ask!

I think I will!

Allen S. Face mire
DP/Director
SaltRun Productions,inc.
Atlanta



Robert Rouveroy wrote :

>The solution was to skip certain frame numbers (NOT TO DELETE OR >DROP THE ACTUAL FRAMES)

Thanks...

I've been gritting my teeth on this one for a while...glad to know there's some folks out there who do, indeed, understand / appreciate the reasons / differences, etc.

I still encounter folks who think the video's affected--that it's something other than a system of counting...

Don Daso
ACME Film & Video
Charlotte NC



Don Daso wrote :

>I still encounter folks who think the video's affected--that it's something >other than a system of counting...

There are also many, many people who think that "29.97=Drop Frame," which is also incorrect (the rate has nothing to do with the counting scheme - you can have 30 DF and you can have 29.97 NDF).

Mike Most
VFX Supervisor
IATSE Local 600
Los Angeles



Mike Most writes:

>you can have 30 DF and you can have 29.97 NDF...

Yes, but I have never encountered a use for them. Who uses them and for what?

Mitch Gross
NYC DP



Mitch Gross wrote :

>Yes, but I have never encountered a use for them. Who uses them and >for what?

If you are shooting film and want to post completely in drop frame, and have no concern for matching back to the negative, 30 DF can be useful (for the sound recording). We did that years ago on "Max Headroom," long before matching back to film was an issue. 29.97 NDF is useful if you're shooting 23.98p video, either HD or standard def using one of the Panasonic cameras.

In fact, in these situations, it's almost always what is used.

Mike Most
VFX Supervisor
IATSE Local 600
Los Angeles



While it is true that DF is appropriate for broadcast (due to keeping clock-accurate)...my understanding is that it really does not matter what format you acquire in, DF, or NDF. It only matters what TC format you post in.

When you create a timeline in DF for a network, it doesn't matter what the tape was shot in...it still creates a time-accurate DF EDL.

We used to argue about this when I was in tv news...and the engineers always said that as long as the tape machines were in DF when we edited and went to air, the acquisition TC format did not matter.

BTW -

I can tell you that from very recent personal experience...the NDF/DF issue is HUGE over the course of a 45 min (re: hour) program. Because of a misunderstanding over which symbol was DF (;) and which was NDF (:) my editor put us more than a minute over. For those who struggle...my college proof always said that you can easily tell the difference because the "comma" in DF appears to "drop" in the semi-colon...compared to the colon

Dan Fox



Allen S. Facemire writes :

>Many thanks to our Dutch friend Robert Rouveroy csc for that >explanation concerning DF vs. NDF in timecode world.

Thanks Allan, thanks Mitch, thanks Don for your kind words, but I have to confess I cribbed a great deal of the gist, the gravamen of the DF vs. NDF story from an article my very good friend Jim Mercer csc wrote in an early issue (1986 or so) of the "CSC Newsletter" that I edited and published in that period.

It was the first time I finally understood what it was all about. That was the time that we (in News and Docu) sort of changed over from film to video. It also helped me figure out how to adapt/convert my Arri 16BL to shoot video off a monitor or even computer screens without those strobing bars. That took care of my retirement, sort of...

Michael Most's observation :

>"There are also many, many people who think that "29.97=Drop >Frame" which is also incorrect (the rate has nothing to do with the >counting scheme - you can have 30 DF and you can have 29.97 NDF).", >now confuses the heck out of me.

Care to elaborate, Michael? This is a fascinating thread...

Robert Rouveroy csc
The Hague, Holland

I plan to live forever. So far, so good.



>I would say that while some of us still shoot network news and >magazine pieces, I'm doing a 22:30 TV show every week which I >supply DV and Beta originals with DF TC but my editor is changing >everything to NDF.

I bet they dub it DF - for commercial insertion they will want the time code to be running in "real time." Certainly, the Canadian networks I've dealt with specify DF TC on the master.

I have never shot any video for any television client - be it a magazine show, sports, news, whatever - in anything BUT drop-frame. Most TV folks wonder why the heck all those film guys are always farting around with NDF time code. (Naturally, they've never had to deal with film matchback)

The only time I ever shoot NDF is when I know the video will be intercut with film - I know that editors can now compensate for this, but it does make their lives easier if the source material is at least consistent.

(And I also know that when you send film to TK and ask for a DF transfer, they will almost always assume you don't know what you're talking about and give you NDF anyway)

I would disagree somewhat with Mitch's comment about TV news being DF - for "accurate running times." No one ever times anything to the frame for TV news - you're often lucky if the time is accurate to within a couple of seconds! And on a typical 2-minute news story, a frame here and there isn't going to make much difference.

George Hupka
Director/DP
Downstream Pictures
Saskatoon, Canada



>Care to elaborate, Michael? This is a fascinating thread...

I'm kind of loathe to, because it will probably add to the confusion.

NTSC time code runs at 29.97 as its native rate. Not 30. However, in order to record double system sound with a film camera running at a crystal 24fps and stay in sync during a telecine transfer, it is necessary to use time code running at 30 fps. This is because all telecines transferring to NTSC are resolved to 23.98, not 24, so in order to stay in sync, the sound must be "pulled down" by the same amount. This is accomplished by resolving the sound to video sync (29.97).

Now, for some reason, many people equate the 29.97 frame rate with drop frame time code. However, the drop frame scheme is a counting scheme - skip two frame numbers every minute except every 10th minute - and has nothing whatsoever to do with the actual frame rate. Thus, you can have either drop frame or non-drop frame counting in either 29.97 or 30 frame code. This has come in handy because when shooting 24p video, you are usually shooting at 23.98. So to stay in sync, the sound must also be recorded at a video rate (29.97) so that it doesn't get pulled down when it's resolved to video sync in post. Hence the need for "29.97 non-drop frame" code.

Have I successfully added to the confusion?

Mike Most
VFX Supervisor
IATSE Local 600
Los Angeles



>Have I successfully added to the confusion?

Yes! Are you talking about shooting film at 30fps or video at 30(true)fps? And if you're talking about shooting video at 30fps, how long has this been an issue and how often is that frame rate used (and for what types of projects) because there aren't that many cameras out there that can shoot a true 30fps, right?

Dan "Opening Cans of Worms" Coplan
Cinematographer/Editor/DVD Authoring



>Are you talking about shooting film at 30fps or video at 30 >(true)fps?...because there aren't that many cameras out there that can >shoot a true 30fps, right?

I wasn't talking about shooting anything at 30fps. I was primarily talking about film shot at 24fps and video shot at either 29.97 (for a standard def camera) or 23.98 (for an HD camera). When I was talking about 30 fps code, I was referring to sound. This all became an issue when electronic post for film television programs began and dailies began to be synched in a video environment.

As for cameras, the only cameras I know of that can shoot "true" 30fps are HD cameras. There are no standard def cameras that shoot 30fps because NTSC is, by definition, a 29.97 (actually 59.94, but let's not get into that) system.

Mike Most
VFX Supervisor
IATSE Local 600
Los Angeles



I've always done stripe & burns for audio post at 29.97 NDF

There's nothing unusual at all about this flavour of timecode.

Sam Wells



>As for cameras, the only cameras I know of that can shoot "true" 30fps >are HD cameras. There are no standard def cameras that shoot 30fps >because NTSC is, by definition, a 29.97 system.

The DVX-100 shoots 30P. I know it gets translated to 29.97, but can you extract the true 30 progressive frames from that mode the way you can extract the true 24 frames in the 24P modes? Would you want to?

I'm sure there's a 'yes' answer in there somewhere, I just don't know what it is. To match to film shot at 30fps?

Dan Coplan
Cinematographer/Editor/DVD Authoring



Dan Coplan

>The DVX-100 shoots 30P. I know it gets translated to 29.97, but can you >extract the true 30 progressive frames from that mode the way you can >extract the true 24 frames in the 24P modes?

True progressive video frames are like film frames or matter - frames are neither created nor destroyed, but you can adjust the length of time each frame is displayed. So, take your 29.97 progressive video into a program like After Effects, set its "frame rate interpretation" to 30 (without deinterlacing), and presto whamo you have 30 fps playback in a 30 fps composition - timeline. In other words, you have "extracted" the true 30 progressive frames. Set the source footage interpretation to 15 fps for the same composition and you have a slow-mo effect, 60 fps will speed it up and so on.

Joseph Kroupa
Cameraman and compositor
Utah



>The DVX-100 shoots 30P. I know it gets translated to 29.97, but can you >extract the true 30 progressive frames from that mode the way you can >extract the true 24 frames in the 24P modes?

"30P" on the DVX100/100A is really 29.97P, and 24P is really 23.976P, and 60I is really 59.94I. All the speeds are off by 1000/1001 and conform to NTSC-compatible rates.

But all those fractional numbers are too big to fit in the menus, grin.

If you want TRUE 30P, 24P, etc., you'll need a Varicam or a CineAlta or the like...or film.

Adam Wilt / Video Geek / Menlo Park CA USA