NTSC Framerates 24 and 30 WHY TWO?? and Xvid AVI

[pbar]

Two questions which MUST have been answered before, but having spent countless hours searching, I have to ask again! -
1. I have AVI files with a framerate of 24 (well, it's 23.79 or something like that) and when burning to DVD using Ulead VideoStudio with the PAL setting, every second or so there's a slight jerkiness. I understand why this is, NTSC to PAL conversion/framerates. But if I was to choose NTSC in VideoStudio instead I assume the jerkiness will go away?
2. Why are there 2 NTSC framerates????? I understand the differences with Pal and NTSC but cannot understand why there's 2 NTSC framerates.
Thanks!

[manono]

Hi-

There's one NTSC DVD framerate, and it's 29.97fps (really 59.94 fields per second). The images can be stored on the DVD at 29.97fps (or 30fps, with the drop_frame flag set), or they can be stored at 23.976fps (or 24fps with drop_frame) with the flags set to perform the telecine (convert 4 frames into 10 fields) and then also output at 29.97fps.

I don't know anything about VideoStudio, nor anything about your jerkiness. Sorry.

[pbar]

Thanks for your reply. Please forgive my ignorance, but you say that there's only one NTSC framerate and it's the one that I referred to as 30 FPS. Well, that's fair enough, but in that case why and what is the lower frame rate (the one just under 24 FPS). Why does that exist!!!????

[manono]

Hi again-

Now I don't understand. You started by saying you have a 23.976fps AVI, but AVIs can be any old framerate you want. I have them from silent film DVDs that I decimated to as low as 15-16fps. Movies, as shown in a movie theater, are 24fps. When put on DVD, they are usually stored on that DVD at 24fps and telecined so that 29.97fps is output by the player. Telecine is adding redundant fields to the mix so that you achieve 29.97fps. It converts 23.976fps to 29.97fps by adding another frame in every 4. 4->5=24->30. In order to minimize any jerkiness that may result, these are added as fields spaced out more or less evenly. Surely at some point you've seen diagrams that illustrate the process. If not, then go here:

http://www.hometheaterhifi.com/volume_7_4/dvd-benchmark-part-5-progressive-10-2000.html

A little ways down you'll come across the first major set of pictures under the heading, NTSC Telecine (Transfer of 24fps Film to 60Hz NTSC TV). It's commonly called 3:2 pulldown.

When you make an AVI from that 29.97fps DVD, you'll perform what's commonly called an IVTC, Inverse Telecine, and get rid of those extra fields, in order to return it to its original framerate.

[pbar]

Thanks for your help and quick response. It's appreciated and I think I'm beginning to understand a little better. So, in effect, if I was to burn the AVI file in question to DVD but choosing NTSC format, then when a DVD player plays it, it will add those extra frames back in, thereby playing a 23.976fps movie at 29.97fps. Which would get rid of the jerkiness (most noticeable with heavy panning scenes, but occuring every second or so) which I get when I burn the file as a PAL DVD. I am getting warmer???? Probably not!

[manono]

Hi-

Like I said before, I have no idea about your DVD program. If it's adding a frame every second to go from 24->25 fps PAL, then that would account for the jerkiness in panning scenes, as you'd get a slight jerk every second from the duplicate frame. It would keep the film the same length, so the audio could be used without adjusting its length. If I were to do it, I'd just speed it up to 25fps, and then adjust the audio accordingly. That's how most 24fps movies are converted to PAL format DVD.

You can check to see what VideoStudio is doing by opening one of the vobs it creates in VirtualDubMod, scrolling to a scene with movement, and then advancing a frame at a time. If you see a duplicate frame every second, I'd say it's time to find another DVD creation software.

As for making it for NTSC format, properly it should be encoded as 23.976 Progressive, with the flags set to output 29.97fps. But again, it depends on the program you use.

Yes, you're getting warmer.

[pbar]

Hi, and again thanks for your help. You are spot on, I checked the DVD MPEG file which VideoStudio created with AVICodec and the framerate has been converted to 25fps - the added frames being the reason for the jerkiness. So, as a test, I used the same program to output an NTSC format MPEG file. I checked that, and the framerate is 29.970fps. (That's no surprise to you I guess) The jerkiness is worse, as I expect there's even more frames added to the original 23.976fps AVI file. (It's a DVD rip of a movie, an NTSC movie my new found expertise tells me). So, I guess I need to (as you mention) convert the AVI to 25fps first before I author it to DVD. (Unless there's DVD authoring software which does it on the fly, I doubt it). Right, back to the How To Guides for that one. Or is it easier to just live with it?! By the way, what program do you use for this? And how come there's no guides to convert 23.976 AVI files to NTSC DVD??? There's loads to convert the AVI to PAL DVD, but not NTSC, how come????

[johns0]

Theres many guides to convert 23.976 to ntsc,all you need to do is use an encoder such as tmpgenc and select ntscfilm and it will output 23.976 mpg2 with pulldown and be played at 29.97 fps,read more guides,do more searches.