[QuadList] Why 29.97? (was 'Re: DVD vs Blu-Ray')

Mon Dec 23 13:04:23 CST 2013

It's actually quite a simpler explanation.  The power companies made 
no changes just for the TV industry:

When NTSC was standardized in 1941 the frame rate was 30.00 fps.  As 
you may know, it was also black-and-white, with 525 lines resolution, 
video carrier at 1.25 MHz and the aural carrier at 4.5 MHz.

When the time came for color, the first standard (NTSC-2, aka 'CBS 
color') was completely incompatible with the black-and-white 
standard.  For various practical and political reasons, NTSC-2 did 
not stick (mostly to do with the Korean War usurping the supplies 
needed to manufacture the new TV sets, but also some deft policital 
manuevering by David Sarnoff and RCA at the FCC to give their 
compatible color system a chance to fix the serious technical issues 
it had in 1950).

The compatible color standard, adopted in 1953 and known as NTSC-3, 
aka "RCA compatible color", used exactly the same resolution and 
carrier structure as B+W NTSC did.  To be able to fit a third signal 
in to the same amount of space, something had to give.  That 
something was the frame rate.

RCA had failed in its demonstrations before the FCC in 1950 because 
the color subcarrier (the signal used to transmit the YIQ color 
signal) produced seriously awful moire patterns in the video due to 
the beating of the color subcarrier (3.60 MHz in the 1950 test 
system) with the visual carrier.  By 1953, the engineers at RCA labs 
had solved the problem: lower the subcarrier frequency slightly to 
3.579545  MHz, AND slow down the frame rate just slightly by 1/1000th 
of a second so the subcarrier interleaved correctly in to the visual 
subcarrier and not cause moire patterns.  Since TV sets in 1953 used 
vacuum tubes instead of hard-coded chips, the receiver circuits of 
the era could handle the 1/1000th of a second difference without 
causing serious issues in older existing B+W receivers.

The line frequency of power nationwide stayed at 60Hz.

And THAT is why we have a 29.97 fps frame rate.

James
------------------------------------------------
James Snyder
Senior Systems Administrator
Library of Congress -
   National Audio Visual Conservation Center (NAVCC)
Motion Picture, Broadcasting & Recorded Sound Division (MBRS)
Packard Campus for Audio Visual Conservation
http://www.loc.gov/avconservation/packard/

>Hmm,
>
>To answer your Trivia Question:
>
>I believe the color subcarrier frequency selected was almost, but 
>not quite, a function of the nation's power grid then known as 60 
>cycles per second.  What I cannot recall is whether the nation's 
>power companies shifted their actual frequency to match...but think 
>they did.
>
>Steve
>
>On 12/23/13 1:36 PM, James Snyder wrote:
>
>>
>>If the label says "NTSC" it means 29.97, not 30fps.  This may seem 
>>to be splitting hairs, but for those of us who archive video 
>>materials there is a meaningful technical difference between 29.97 
>>fps and 30 fps.  There actually is 30 fps material being produced 
>>today, and it doesn't always play nicely with 29.97 equipment 
>>unless it's slowed down properly.
>>
>>PAL and SECAM (and all 576 line digital video) is 25.00 fps, of course.
>>
>>Then there is the whole Drop Frame vs. Non-drop frame time code 
>>thing.  I can't wait for the day when we no longer need Drop Frame 
>>time code.
>>
>>Additionally, "YUV" is a misnomer as well.  YUV is the term used 
>>for PAL & SECAM variant of YPbPr  component color difference 
>>encoding in the ISO international analog television standards.  YIQ 
>>was NTSC's term.  YPbPr is the proper terminology for component 
>>color difference signals, like those used in MPEG-2 encoded video 
>>on DVDs.  Hence, you CANNOT use the term "YUV" when talking about 
>>NTSC coded video. Oh, the irony.  However, since "YUV" seems to be 
>>easier to use as a term than "YPbPr" to the vendors who write the 
>>manuals, software and documentation (and most of those vendors are 
>>in former YUV countries) the misuse of YUV terminology continues.
>>
>>Trivia question for the group: why does the 29.97 frame rate exist?
>>
>>James
>>
>>------------------------------------------------
>>James Snyder
>>Senior Systems Administrator
>>Library of Congress -
>>   National Audio Visual Conservation Center (NAVCC)
>>Motion Picture, Broadcasting & Recorded Sound Division (MBRS)
>>Packard Campus for Audio Visual Conservation
>><http://www.loc.gov/avconservation/packard/>http://www.loc.gov/avconservation/packard/
>>
>>>Sometimes the NTSC label simple means 30 fps, and PAL 25fps
>>>
>>>Robert
>>>
>>>RMC Media Partnership
>>>
>>>On Mon, Dec 23, 2013 at 5:24 PM, Steve White 
>>><<mailto:Steve.White at 800callnow.com><mailto:Steve.White at 800callnow.com><mailto:Steve.White at 800callnow.com>Steve.White at 800callnow.com> 
>>>wrote:
>>>
>>>
>>>
>>>Fred & Tony,
>>>
>>>Thank you for your replies.  Both are helpful.
>>>
>>>I did not have VLC.  Just downloaded it from cnet.  VLC reports:
>>>
>>>Codec: MPEG-1/2 Video (mpgv)
>>>Resolution: 720x480
>>>Decoded format: Planar 4:2:0 YUV
>>>
>>>Which leaves just one question.  Is it technically correct to 
>>>label this as an NTSC DVD, or should it be labeled something else?
>>>
>>>Warm regards,
>>>Steve
>>>
>>>
>>>On 12/23/13 12:07 PM, Fred Kovach wrote:
>>>
>>>>Hi Steve,
>>>>
>>>
>>>It prob is 480i anamorphic.  Many bluray players will play 
>>>whatever is in them at 1080p. Anamorphic refers to a 16:9 being 
>>>squeezed into a 4:3 picture, which is then stretched out to the 
>>>full 16:9 screen on the monitor.
>>>
>>>That being said, TQ's advice to use VLC is your best between to 
>>>find out what format it's in.
>>>
>>>Take care,
>>>Fred
>>>
>>>Fred and Crystal Kovach,
>>>along with Phillip, Stephen and Hope.
>>>
>>>Your missionaries using media technology to reach our world for Jesus!
>>>Voice: <tel:417.848.8381><tel:417.848.8381>417.848.8381
>>>Main Webpage: 
>>><http://www.fredcrystal.com/><http://www.fredcrystal.com/><http://www.fredcrystal.com>www.fredcrystal.com
>>>Ministry Information: 
>>><http://ministry.fredcrystal.com/><http://ministry.fredcrystal.com/><http://ministry.fredcrystal.com>http://ministry.fredcrystal.com
>>>
>>>Sent from my iPhone
>>>
>>>On Dec 23, 2013, at 10:53 AM, "Steve White" 
>>><<mailto:Steve.White at 800CallNow.com><mailto:Steve.White at 800CallNow.com><mailto:Steve.White at 800CallNow.com>Steve.White at 800CallNow.com> 
>>>wrote:
>>>
>>>>Thanks for the opportunity to ask, can someone help me get a 
>>>>better grasp of DVD vs Blu-Ray formats?
>>>>
>>>>I recently received a video disc labeled as an NTSC DVD of the 
>>>>Garth Brooks "Blame It All On My Roots" performance in Las Vegas. 
>>>>Playback on my Blu-Ray deck displays as full screen on a new 
>>>>Panasonic plasma screen capable of 1080p without obvious aspect 
>>>>ratio distortions.
>>>>
>>>>Garth's performance is incredible; lighting, camera work, audio, 
>>>>direction all are great.  Apparently, there is currently no 
>>>>Blu-Ray disc available.
>>>>
>>>>- Is it technically correct to label the DVD as NTSC when the 
>>>>image displayed is 16:9?
>>>>
>>>>- What's the likely resolution/format?  Any suggestions on how I 
>>>>could have confirmed that without asking you?
>>>>
>>>>Many thanks,
>>>>Steve
>>>>
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