Film-Tech Forum ARCHIVE: Timecode on NTSC.

This is topic Timecode on NTSC. in forum Film-Yak at Film-Tech Forum ARCHIVE.

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Posted by Stephen Furley (Member # 1277) on 07-24-2005, 08:30 AM:

On PAL it's simple, the frame count runs from 0 to 24 in each second, but how does timecode work in NTSC, given the fractional number of frames per second?

Posted by Leo Enticknap (Member # 534) on 07-24-2005, 09:39 AM:

When I'm editing NTSC in Adobe Premiere, the frame count just goes from 0 to 29. I presume that the first or last frame is only displayed for 0.97 of second, or that all the frames are very fractionally shorter than a second to bring the overall fps rate down. I don't know the answer for sure, though.

Posted by Andy Summers (Member # 3207) on 07-24-2005, 10:12 AM:

Hallo there all

I’ve just fired up the Pioneer CLD 1750 Laserdisc player, one of two that I have and ran a PAL version of “FAR AND AWAY” PLFEC 35571 side 3 CAV and the frame count came in at 26fps 1sec, then I ran a NTSC version of “RETURN OF THE JEDI” the older version CBS/FOX VIDEO 1478-85 and the frame count came in at 31fps 1sec.

Strange I though it was 25fps 1sec for PAL and 24fps 1sec for NTSC, no mater if I can see the image fine.

As for the image on “FAR AND AWAY” I ran the DVD Region 2 version and noticed the frame area on the Laserdisc had more height too it, and far less on the DVD, however noticed just a little bit more width on the DVD.

Leo, is there any reason for this frame count difference, given that video as differences in these areas, and film playback is 24fps 1sec world wide can’t any one with all this technology make it universal.

Sorry to drift of the topic over to you Stephen….

Posted by Mark Ogden (Member # 43) on 07-24-2005, 10:31 AM:

NTSC, and all US broadcasting, utilizes what's called "drop-frame" time code, but that's actually an inaccurate name as no frames are dropped, just their TC numbers. What happens is that at the top of every minute of running time code, the first two frames have no count (for instance, the first counted frame after TC 1:00:02:29 would be 1:00:03:02). This holds true except when the minutes are multiples of 10 (20, 30, 40 and so on) when each frame has a valid TC. Somehow it all pans out math-wise in the end.

You can also stripe non-drop frame, but because of the fractional NTSC frame rate you will not wind up with an accurate duration at the end of a long program. This is OK for a shorter length item, but you'll wind up with an unaccounted-for 54 frames or so at the end or an hour program.

[ 07-24-2005, 02:19 PM: Message edited by: Mark Ogden ]

Posted by Gordon McLeod (Member # 33) on 07-24-2005, 10:32 AM:

NTSC is claimed to be 30fps since video syncs to the line frequency in our case 60Hz 25fps synces to 50Hz
In fact it is approximately 29.5
Also there is different drop frame systems used as well

Posted by Bernard Tonks (Member # 809) on 07-24-2005, 11:13 AM:

As a former video facilities operator in television, I should know all about this, but don’t have sufficient knowledge to explain. We handled film, and every video format known for Archive, TX and contract work. Except for 2” Quad, which I only had brief training on at Ravensbourne College.

Hope this website is useful:
http://www.amek.com/oldsite/datashee/timecode.htm

Posted by Stephen Furley (Member # 1277) on 07-24-2005, 11:19 AM:

quote: Andy Summers

Strange I though it was 25fps 1sec for PAL and 24fps 1sec for NTSC, no mater if I can see the image fine.

PAL is 25 frames per second and NTSC is 29.97. These frame fates are laid down in the standards for the video systems and do not change. Film is usually 24 frames per second, but other speeds are sometimes used for special purposes. You can run film at any speed you like up to the point where either the film itself or the camera mechanism is damaged. Fairly conventonal camera mechanisms can run at over a hundred frames per second, special ones with a rotating prism and continuously moving film can manage several thousand. If only the television people had adopted one standard world-wide film would probably have been altered to match by now, and there would be one standard speed for everything. As it is now, increasing the film speed to 30 would improve things for NTSC transfers, but make them worse for PAL

quote: Andy Summers
As for the image on “FAR AND AWAY” I ran the DVD Region 2 version and noticed the frame area on the Laserdisc had more height too it, and far less on the DVD, however noticed just a little bit more width on the DVD.

Video transfers are not always accurately made; you quite often see less, or more, than you were intended to in either direction.

Posted by Leo Enticknap (Member # 534) on 07-24-2005, 03:28 PM:

quote: Andy Summers
Leo, is there any reason for this frame count difference, given that video as differences in these areas, and film playback is 24fps 1sec world wide can’t any one with all this technology make it universal.

The reasons for the NTSC and PAL (and PAL's 405-line predecessor) standards becoming established in the form that they now exist, and the reasons for their fundamental incompatibility with 24fps film boil down to a fearsomely complicated mix of engineering, politics and corporate power struggles. This book, in my opinion, is a good place to start. This one explains the history and development of telecine (film to video transfer) technology and the various ways which exist to get round the speed, scanning rate and interlacing compatibility problems.

Posted by Stephen Furley (Member # 1277) on 07-24-2005, 04:50 PM:

I've got a copy of 'Film into Video', but when I'd read the first few chapters somebody borrowed it from me and she hasn't given it back yet. That was a couple of years ago.

It just seems a shame that they couldn't have put aside the political issues, resolved the technical ones, and got everything compatible from the beginning.

Posted by Leo Enticknap (Member # 534) on 07-24-2005, 05:10 PM:

I know the feeling - I've got a hit list of people who borrowed books months or years ago: so much so that I'm now reluctant to lend them to anyone other than colleagues and friends I know I can trust.

Tube is an excellent book, IMHO: the storytelling is done well enough to keep you reading (unlike many academic history books, which cover issues chunk by chunk and leave the reader to work out the links, which can be hard work even the reader knows a bit about the subject to start with) and you're given enough biographical information on the principal characters (especially Baird, Farnsworth, Zworykin & Sarnoff) to bring them to life a bit. But, the authors don't dumb down the technical side and leave out the nitty gritty details. It's a pity this book is no longer in print.

Posted by Bruce Hansen (Member # 281) on 07-25-2005, 11:47 AM:

The reason for the different frame (or field) rates has to do with power line frequency. The power in places like England is 50 Hz, here in the US it is 60 Hz. The field rate was made the same as the power frequency so that any small amount of power "hum" that ended up in the picture would not be moving through the picture, and not be noticeable. Of course, when we added color here in the US, the scanning rates were changed slightly, so that everything would be coherent with the color sub carrier, and that gave us a 59.94 vertical rate. Now you will see hum as dark and light bands moving slowly up the screen, but equipment is better than it was years ago, so the hum problem is not much of a problem any more.

Non-drop frame code is OK for something where you are not concerned about knowing the exact running time, and can be easier to edit with. If you are editing something for broadcast, you should use drop frame. Most edit systems today can handle the two types of code, and even intermix them.