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 Post subject: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 05 Dec 2017, 00:57 
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[I'm working with NTSC]. I'm still learning the means and methods of 3:2 pulldown (for film source on video). For years I just transferred my LD's to dvd and called it good, using s-video at that :cry: Had no clue about the necessity of a 3D comb filter. My Sony Wega hd crt has a great 3d comb filter so I never knew (most) capture devices/pci cards do not. Watching on the tv looked great. Just assumed my captures would also look the same.

I'm confused how the audio stays in sync if either:

1) a video processor does the IVTC before the video goes to the capture device
2) you do the pulldown in your video editing program via rendering
3) you manually cut the repeated frames in your NLE (I imagine this method would take forever to cut all the added frames)

The only method of these three options that I fully understand at the moment is manually cutting the repeated frames. And I know when you do that you are also cutting the audio track as well. And depending on the location, it could be a crucial spot in the audio track where the cut would be really noticable.

How do you go from 24fps (original film mag or optical track) to 30 (home video LD/VHS etc), back to 24 (IVTC), where the audio has already been designed to fit at 30fps, then synced in back at 24? But I guess the same question could be asked; how can the audio sync what was originally at 24 now at 30 (for video).
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 Post subject: Re: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 05 Dec 2017, 01:15 
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The short answer is that the audio is played at a constant speed, & the picture is played at a constant speed. One second of audio doesn't care whether it's accompanied by 24 film frames, or 30 video frames. So, when the film is converted to video, 24 frames are mapped to 30, but the running time remains the same ; and undoing that mapping process, likewise, 30 frames become 24, but each of those frames occupies more time. If you were just to cut out the repeated fields, you'd be left with fewer frames & less running time, & then you'd have to stretch them out by 20% to get the correct running time.
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 Post subject: Re: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 05 Dec 2017, 01:51 
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publius wrote:
If you were just to cut out the repeated fields, you'd be left with fewer frames & less running time, & then you'd have to stretch them out by 20% to get the correct running time.


Ok, I think I'm getting my fields and frames mixed up. When you say "if you were to cut the repated fields, you'd be left with fewer frames and shorter running time"...

I thought the repeated images were frames, not fields.
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 Post subject: Re: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 06 Dec 2017, 19:58 
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clashradio wrote:
publius wrote:
If you were just to cut out the repeated fields, you'd be left with fewer frames & less running time, & then you'd have to stretch them out by 20% to get the correct running time.


Ok, I think I'm getting my fields and frames mixed up. When you say "if you were to cut the repated fields, you'd be left with fewer frames and shorter running time"...

I thought the repeated images were frames, not fields.


The repeated images are frames written into fields.
Film frame A is written into Video Frame 1, Fields 1 & 2
Film frame B is written into Video Frame 2, Fields 1 & 2 and Frame 3 Field 1
Film frame C is written into Video Frame 3, Field 2 and Frame 4 Field 1
Film frame D is written into Video Frame 4, Field 2 and Frame 5 Fields 1 & 2

Frame numbers are assigned:
Frame 1 - both fields
Frame 2 - both fields
Frame 3 Even Field + Frame 4 Odd Field
Frame 5 - both fields

During playback all 5 frames play for true 30 (29.97) fps, but during freeze frame, Fields 3 Odd and 4 Even are not displayed.

Of course, this is assuming the Telecine was done properly. LOTS of DiscoVision CAV titles, while running at 24fps still have jitter freeze frames because the incorrect fields were flagged as complete frames.


Last edited by blam1 on 07 Dec 2017, 01:30, edited 1 time in total.
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 Post subject: Re: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 06 Dec 2017, 23:02 
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blam1 wrote:
Of course, this is assuming the Telecine was done properly. LOTS of DiscoVision CAV titles, while running at 24fps still have jitter freeze frames because the incorrect fields were flagged as complete frames.


Thank you for your explanation. I'm having a hard time understading what the definition of "fields" mean. I know it has to do with interlacing. I'll do some more research.
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 Post subject: Re: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 07 Dec 2017, 00:22 
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Shortly put, the whole thing about 3:2 pulldown that makes it work is that, while video runs at 30 frames per second, it does so in two steps. First half the lines are scanned, in 1/60 second, then the remaining lines in the remaining 1/60 second. The two sets of lines are "interlaced" as you do with your fingers, first a line in the first field, then a line in the second field, then back to the first field, & so on.

So, as a result, the easiest way to deal with film running at 24 frames per second and video at 30 is to recognize that both are multiples of 120. Each video frame occupies 4/120 second, & each video field occupies 2/120, while each film frame occupies 5/120. So, your first frame is held in the film gate for the period of two fields or one frame, that is, 4/120, and then "pulled down" to make way for the next one, which is held for three fields or 6/120. Since 4+6=10, the two successive film frames occupy 10/120 second, & two-and-a-half successive video frames occupy 10/120, so everything works out fine.

The main thing to realize is that each & every film frame is represented either by two or by three successive video fields. In other words, either a complete picture in two halves, or a complete picture plus a half of a picture repeating the first half of the previous picture. It is, therefore, possible to recover the original film frames. The only exception occurs when video editing has been done after the film-to-video transfer step, in which case you may be left with occasional partial frames. This is, however, rare. Much more common are "cadence shifts", in which the regular 3:2:3:2:3:2 sequence of fields stutters, giving 3:2:2:3 or 2:3:3:2 sequences. These cause no problems to the viewer, but schemes which rely on detecting the sequence of fields often react badly.
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 Post subject: Re: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 07 Dec 2017, 00:29 
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Isn't this just another question about how to make copies of films that have a copyright on them????
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 Post subject: Re: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 07 Dec 2017, 14:38 
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rein-o wrote:
Isn't this just another question about how to make copies of films that have a copyright on them????


It's got nothing to do with copyrights at all. Some tv's have built in 3d comb filters, and auto 3:2 mode. My Sony Wega has this Cinemotion mode: "provides an optimized display by automatically detecting film content and applying a reverse 3/2 pulldown process. Moving pictures will appear clearer and more natural looking".
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 Post subject: Re: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 07 Dec 2017, 16:03 
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Copy is copying and is copyright infringement.
Words kind of go together.

And correct me if i'm wrong, all of your issues are due to the fact that you are copying something, right????
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 Post subject: Re: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 07 Dec 2017, 23:16 
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rein-o wrote:
Copy is copying and is copyright infringement.
Words kind of go together.

And correct me if i'm wrong, all of your issues are due to the fact that you are copying something, right????


Yes, I guess you're right. Am I wrong to transfer my vinyl to cd? My cd's to my I-Pod, my laserdisc's to BD?
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 Post subject: Re: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 07 Dec 2017, 23:21 
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publius wrote:
Shortly put, the whole thing about 3:2 pulldown that makes it work is that, while video runs at 30 frames per second, it does so in two steps. First half the lines are scanned, in 1/60 second, then the remaining lines in the remaining 1/60 second. The two sets of lines are "interlaced" as you do with your fingers, first a line in the first field, then a line in the second field, then back to the first field, & so on.

So, as a result, the easiest way to deal with film running at 24 frames per second and video at 30 is to recognize that both are multiples of 120. Each video frame occupies 4/120 second, & each video field occupies 2/120, while each film frame occupies 5/120. So, your first frame is held in the film gate for the period of two fields or one frame, that is, 4/120, and then "pulled down" to make way for the next one, which is held for three fields or 6/120. Since 4+6=10, the two successive film frames occupy 10/120 second, & two-and-a-half successive video frames occupy 10/120, so everything works out fine.

The main thing to realize is that each & every film frame is represented either by two or by three successive video fields. In other words, either a complete picture in two halves, or a complete picture plus a half of a picture repeating the first half of the previous picture. It is, therefore, possible to recover the original film frames. The only exception occurs when video editing has been done after the film-to-video transfer step, in which case you may be left with occasional partial frames. This is, however, rare. Much more common are "cadence shifts", in which the regular 3:2:3:2:3:2 sequence of fields stutters, giving 3:2:2:3 or 2:3:3:2 sequences. These cause no problems to the viewer, but schemes which rely on detecting the sequence of fields often react badly.


Thank you publius for your explanation.
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 Post subject: Re: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 09 Dec 2017, 19:27 
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clashradio wrote:
rein-o wrote:
Copy is copying and is copyright infringement.
Words kind of go together.

And correct me if i'm wrong, all of your issues are due to the fact that you are copying something, right????


Yes, I guess you're right. Am I wrong to transfer my vinyl to cd? My cd's to my I-Pod, my laserdisc's to BD?

I don't know, what do you think.

And if you are just getting LD to transfer to BD you technically aren't really wanting to "collect" LDs you just want to capture the footage. Right??
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 Post subject: Re: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 09 Dec 2017, 20:31 
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rein-o wrote:
clashradio wrote:
rein-o wrote:
Copy is copying and is copyright infringement.
Words kind of go together.

And correct me if i'm wrong, all of your issues are due to the fact that you are copying something, right????


Yes, I guess you're right. Am I wrong to transfer my vinyl to cd? My cd's to my I-Pod, my laserdisc's to BD?

I don't know, what do you think.

And if you are just getting LD to transfer to BD you technically aren't really wanting to "collect" LDs you just want to capture the footage. Right??


If I understand correctly, as long as I keep the original medium it's ok to transfer. How do you explain people putting their music on their mobile devices? And most of those Hipster's sell their original cd's once ripped.

Who said anything about selling my LD's? I've had some for 15 years. Some I just got (Japanese Special Collection). Even if these were put to BD officially
I wouldn't sell my LD's.
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 Post subject: Re: audio sync after 3:2 pull-down?/transfering to BD
PostPosted: 10 Dec 2017, 01:09 
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Just found this, pretty funny.
Don't judge me, the judge will judge you.
According to this no monies were exchanged :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol:
http://www.imdb.com/title/tt0120915/trivia?item=tr2015576

A few USC students took the Japanese LaserDisc and made their own edit of the movie. Contrary to popular belief, it does NOT cut out all scenes featuring Jar-Jar Binks, but does remove many of his sillier and more distracting moments, and makes many other minor tweaks. It became known as the "Phantom Edit". George Lucas requested to see a copy, and then Lucasfilm issued a press release reiterating that it is illegal to copy and/or edit a Lucasfilm property.
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