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Seeking DF/NDF enlightenment…
Hi
Can you offer clarification on seemingly incompatible statements by two experts?
Here’s a quote from a colleague:
“I’ll say it all again, 23.98 MUST be DF or the TC doesn’t agree with real time, and since the only reason for ever shooting 23.98 is to get a 2:3 or 2:3:3:2 pulldown to 59.94, the TC MUST be DF or the 59.94 is wrong. There’s no way round this, it’s a fact of life.”
https://forums.dvdoctor.net/showthread.php?p=283592#post283592This was in response to two Gary Adcock posts this in this forum in January:
“24p in all formats is NonDrop, not just 720, but 1080 and SD are all non drop in 24.
“So if I shoot 24p it is 24p and not 23.976, is this right?”
NO, NO, NO, 24p video is 23.98. The HVX 200 only has the ability to shoot at 24.0 fps with the EU version of the camera (and the camera needs the ability to be set to 60 hrz , not 59.94)
24p content in video is considered / expected @ 23.98 so that it can directly downconvert to 29.97,
24.0 content needs custom conversion tools not found in most suites to make the video playable in NTSC at 29.97Frame Rates below 30hrz are only NDF
Frame Rates at 30hrz or above can be either drop or non drop.
720p60 (as 60hrz or as 59.94hrz) can be drop or non drop.”
https://forums.creativecow.net/readpost/193/863332?univpostid=863306&pview=t -
8 Replies
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Editors in the UK do not regularly deal with DF timecode, as 25 is NDF.
While I do a lot of work in the UK and the EU, I am based in the US and deal with these issues daily
Just because the TC Looks like DF does not mean that it is, the recording is actually slowed down at the tape head during recording and playback so that we are able to do realtime downconvert to NTSC.
gary adcock
Technical Chair for HD Solutions and the Director of Photography Track
NAB 2007 Post Production Conferencesgary adcock
Studio37
HD & Film Consultation
Post and Production Workflows -
[PaulD] “Here’s a quote from a colleague:
“I’ll say it all again, 23.98 MUST be DF or the TC doesn’t agree with real time, and since the only reason for ever shooting 23.98 is to get a 2:3 or 2:3:3:2 pulldown to 59.94, the TC MUST be DF or the 59.94 is wrong. There’s no way round this, it’s a fact of life.””I am afraid your colleague is VERY WRONG on this point. In a 60hz camera such as the HVX200, the 24p modes (23.98) timecode is ALWAYS NDF there is no way to set it to DF. Regardless of what it may have been previously set to, when switched to 24p mode it will automatically record NDF timecode.
A lot of people seem to be of the understanding that because a frame rate is not a whole number, eg. 23.98, 29.97, 59.94, that it is DF timecode but that is not the case. For instance with 29.97, you could have NDF or DF timcode. -
Yeah, this is pretty confusing, is this true only in the HD world. In SD 29.97 and 23.98 are in fact always DF?
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The original B+W signal in the US was 30 frames per second (60 Hz). My understanding is that when the color subcarrier they changed the signal to 29.97; something to do with adding the color burst, I’d have to go look it up. PAL already had color, so it is a true 25 (50 Hz) frames per second. Don’t confuse Drop Frame and Non Drop Frame with the cycles per second. PAL has no NDF or DF mode as it is timed perfectly. In NTSC though, 30 frames come in 29.97 seconds or 24 frames come in 23.98 seconds. NDF is just letting this run as is. You can see what happens 30 frames occur slightly faster than 30 seconds so over a half hour or hour show your video clock has run ahead of your real time clock. DF time code drops a couple of frames per minute to slow the video clock back down and make video time equal to real time. This is only really important when you are doing broadcast work. We used to do everything in DF, but then found we had more DVD errors in DF than NDF. Now we do everything in NDF and just convert it if we need to sent it out for broadcast, which is only a small amount of our work anyway. This is my overly simplified understanding of the issue and it may not be exactly correct, but it gives you some idea that there are two distinct issues regarding NTSC Time code.
Aloha,
Ken
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[ken hon] “DF time code drops a couple of frames per minute to slow the video clock back down and make video time equal to real time.”
This is another reason people get confused on this issue. DF timecode DOES NOT DROP FRAMES!
It just drops the count of the frames. This is a very simplified explanation. Look at these two counts and you will see what I mean.
1,2,3,4,5,6,7,8,9.
1,2,3,4,5,7,8,9,10.
There are still 9 frames in each of these counts, however you will notice that the number 6 is not in the second count. That is kind of how drop frame timecode works. It just skips numbers in the counting process. It doesn’t skip or drop frames. Maybe it’s the name that really confuses people. -
[msacci] “Yeah, this is pretty confusing, is this true only in the HD world. In SD 29.97 and 23.98 are in fact always DF?”
No! In SD 29.97 can be either DF or NDF. 23.98 is NDF.
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Aloha Frank,
You are of course correct, sorry about my sloppy wording. As you state only the frame count in the time code is dropped, not any frames.
Thanks Frank.
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my head hurts.
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