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3:2 on laserdisc question

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Alright, maybe I'm too used to modern eletronics to solve analog problems.... Is laserdisc encoded 24fps and applies 3:2 on the fly? Or is the disc encoded 29.97. The reason I ask, is I've captured quite a chunk of ANH from the Faces set, and my pulldown is not consistent. It holds for the duration of a scene, but then it switches. (I.E. from WWWSS to WWSSW).
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It's good ol' NTSC encoded at 29.97 - Pal at 25.

Gotta love that analogue goodness.

As far as your trouble is concerned, I have no clue. It could be due to the fact that the program is not getting the right fields into their correct frames.

Edit: Crap, I should read posts more carefully before I reply. Sorry for the redundant/useless answer. I'm actually clueless as to why this is happening. I'm not very experienced.

maybe this'll help: http://www.doom9.org/ivtc-tut.htm

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The changing 3:2 pulldown setting throughout the film is unfortunately normal for film on NTSC laserdisc (and VHS), I have yet to find an NTSC film on laserdisc where I can apply a single setting that'll undo the a whole side, you have to manually go through the captured video finding out what sections need what undo settings to fully undo the 3:2 pulldown with no glitches (as you get with any automatic 3:2 pulldown filters)
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***Citizen's NTSC DVD/PAL DVD/XviD Info and Feedback Thread***
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grrrr... well that's a royal pain in the ass. Thanks for the feedback. I wonder why that is? I mean normally you'd have a 24fps master of the film on which you applied an even 3:2 the whole way down. It's almost like they had pieces and parts which were telecined at different times, and then they edited them together. What do you suppose they made Faces from? A 2" master?
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It might be that when it was being "encoded" (as far as the word holds for Laserdisc), they made sure that any scene changes would only happen on a complete frame ("frames" in this sense usually start, I think, with the bottom field first). There's also the time compression issue - sometimes a percentage of the repeated fields are removed in order to fit the film on two sides.

If only you guys had gone with a 50Hz electrical supply...

DE
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Originally posted by: Darth Editous

If only you guys had gone with a 50Hz electrical supply...

DE



double grrrr.... every day is a new adventure in NTSC land. 25=25=25. simple. here it's 24=23.98=29.97. Wha? It's hard for me to watch PAL because that scan rate looks shimmery to my Amercanized cortex. I've been ruined.

So I haven't yet found a plugin for Shake that allows automatic 3:2 detection (with scene detection). And even for After Effects there's a plugin that's Windoze only. Anyone know of something like this for Mac?
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Ok here's a spanner for the "3:2 pulldown on LD" works:

The definitive set and the Criterion Blade Runner are both 24fps film on NTSC CAV, which means when you play them back you get 29.97fps 3:2 pulldown footage, if I play them on my Pioneer CLD-D515 and press pause during playback I get a still picture because the discs are CAV, if I then advance or go back frame by frame there's no sign of any 3:2 pulldown...

Does anyone have an answer to that one? I asked on a laserdisc newsgroup but nobody bit.
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***Citizen's NTSC DVD/PAL DVD/XviD Info and Feedback Thread***
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25=25=25. simple. here it's 24=23.98=29.97.


Actually it's more like 24=25=25, which means us PAL watchers are used to watching almost every imported movie or filmed TV show at a higher pitch. Enterprise, for example - T'Pol sounds a lot lower on the downloads than she does on TV. But we do get a 1:1 ratio of film frames to video frames.

Recent showings of Stargate sound like they've tried to squeeze the audio rather than simply resampling it - it sounds the right pitch but has the occasional glitch. None of which helps you, CharlieX, but I think it's interesting

I could probably knock something up in C that could strip out repeated frames/fields (depending on how it was captured) but you'd have to feed it an image sequence (one Targa file per frame), and at 1mb per frame you'd need a lot of storage.

DE
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Does anyone have an answer to that one? I asked on a laserdisc newsgroup but nobody bit.


Any sign of any fully repeated frames? When I grabbed some of my NTSC laserdiscs I found they repeated every fifth frame, not every fifth field, but I don't know if that's down the capture card or the laserdisc.

Now you come to mention it, I ran my Mission: Impossible side 3 (NTSC CAV) at 1/30th speed and couldn't spot any repeated frames either... spooky.

DE
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There MUST be time compression in NTSC Faces. There's a scene up front with the soldiers running through the halls of the blockade runner, just before you cut to the 2nd time we see 3PO/R2. The 3:2 is going along evenly....and then BLAM there's a repeated frame. After that the 3:2 has shifted. What FUBAR.

But that would actually be time EXPANSION. . .
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This is what Laserman posted in another thread; you may find it useful:
3:2 Pulldown. This is where it gets frankly amazing. You all know that for NTSC they do the perverse 3:2 pulldown, wherin you use a film frame for the first 3 fields, then grab the next frame and use it for 2 fields, and then start again. (Grabbing the next frame is referred to as 'pulling it down' hence the 3:2 pulldown name. They used to just repeat the 4th frame which gives the awful juddering you can see on some early telecines.
Now to do this on Laserdisc, they player has to know which two adjacent fields actually make up the frame (othewise you might get one field from one frame of film, and the other field from a diferent frame - not good). So how does an analogue system cope with this? Easy, encode the required information in the VBI (the vertical blank interval). When making the disc, you store the info in the VBI, its often referred to as a 'white flag'. When you hit the pause button on a CAV disc, it reads the flag, and the laser assembly actually does a one track reversal (i.e. 2 fields) and can then redisplay the current frame. It is set in the VBI area outside of picture info, or CC info (its at line 11 or 274 depending on the field). If you get it wrong, the pause feature will have a 'jiggling' frame for 40% of the frames! You can see this on some discs. Sometimes just the 'picture number' is used instead, which is also encoded into the VIL.

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What it comes down to is that the pulldown can change anytime they needed a reel change when encoding the laserdisc. When making the disc, they had no concern if half a frame was interlaced incorrectly, since you won't notice it while watching. So no attempt was made to sync up the frames when reels were changed.

It's quite common for laserdiscs to alter the pulldown frames many times per disc. You can usually find the spot where it changes by scanning through cuts. Just be careful, sometimes it'll change back to the original settings by the end of the disc, making it easy to miss the change.
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I didn't want to hijack Farsight's thread any more, so I've dragged this into a more appropriate thread:
Originally posted by: THX
How does on-the-fly PAL to NTSC conversion work? Are PAL DVDs generally encoded at 24fps progressive, with the PAL player converting to 25fps? If so, does the PAL/NTSC player apply 3:2 pulldown to get to 29.97 at true speed, or is it somehow still played at PAL's 104% speed?
Originally posted by: Laserman
All decent film DVDs are stored as 24fps on the disc itself. No DVDs store anything as progressive, it is an interlaced system - but the two fields stored make up exactly one film frame, so the end result is the same really.
Originally posted by: Citizen
PAL films are generally stored progressive but at 25fps instead of 24fps (no framerate conversion, just plays back faster) with the audio sped up to match the faster playback rate.
First of all, thank you Laserman and Citizen for your answers. I don't think either of you answered my second question, probably because I phrased it badly, so I'll try to get at what I mean a different way, informed by your previous answers:

Does a PAL/NTSC DVD player play PAL discs on NTSC displays at true speed or PAL speed?
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Originally posted by: THX
Does a PAL/NTSC DVD player play PAL discs on NTSC displays at true speed or PAL speed?

PAL speed. The only 'DVD player' I know of that can play PAL DVDs at true speed is the latest WinDVD, it has an option called "PAL truspeed", using this means you have the added benefit of the higher PAL resolution coupled with the correct playback speed.
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***Citizen's NTSC DVD/PAL DVD/XviD Info and Feedback Thread***
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Does a PAL/NTSC DVD player play PAL discs on NTSC displays at true speed or PAL speed?


I've only ever come across one standards-converting DVD player, and that only converted from NTSC to PAL by dropping every nth frame.

If there is a player than converts from PAL to NTSC (and I doubt there is), if it didn't stick to PAL speed it would have to decode and resample the audio.

I think it's InterVideo's DVD software that has a "PAL Truespeed" option - it slows PAL discs down to 24fps and resamples the audio, but this breaks the outputting of AC3/DTS on a SPDIF output.

DE
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My portable DVD player has a switch on the back saying "PAL* *NTSC" so I can output any DVD as PAL or NTSC without having to go into the player's settings and restart the disc like my standalone player, it doesn't slowdown or speedup films but does do on-the-fly framerate conversion which is pretty good (I've seen terrible results on some expensive non-budget players).
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***Citizen's NTSC DVD/PAL DVD/XviD Info and Feedback Thread***
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Originally posted by: CharlieX
Alright, maybe I'm too used to modern eletronics to solve analog problems.... Is laserdisc encoded 24fps and applies 3:2 on the fly? Or is the disc encoded 29.97. The reason I ask, is I've captured quite a chunk of ANH from the Faces set, and my pulldown is not consistent. It holds for the duration of a scene, but then it switches. (I.E. from WWWSS to WWSSW).


Yes the responses are correct - it is 29.97fps for NTSC LD (and for NTSC VHS)

On the SW Definitive there are pattern changes, not only at the side breaks, but often halfway through the sides.
I have tried a few automatic 3:2 pulldown removal plugins (VDub and even TMPGEnc frame conversion), but by far the best result is to use AVISynth (and send to VDub) and do a reconstruction according to the pattern that you see and see if it changes by scanning through a side at a time. You may need to add frames here and there (be sure to note where you add them) and some of these can be removed later via the script.

If you are interested in a script sample, I can post it here

ntrprs
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Bit off-topic, but whenever I use AVISynth the result is always darker than the input. Anyone else noticed this, or found a way around it?

DE
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Originally posted by: Darth Editous
If there is a player that converts from PAL to NTSC (and I doubt there is), if it didn't stick to PAL speed it would have to decode and resample the audio.
Both my last two budget players were quite happy to play back PAL encoded discs in NTSC .

Anyhow, if PAL films are generally stored progressive but at 25 fps and a PAL/NTSC player plays PAL discs at PAL speed in NTSC, then the player must be doing some kind of pulldown other than 3:2, or dropping a frame every second - or am I missing something?
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PAL is interlaced, just like NTSC. For some reason people confuse interlacing with 3:2 pulldown. It's not the same thing.

Interlacing: a method of "drawing" images on a screen by "sketching" every other scanline first before completing it with the other half.

3:2 Pulldown: a method of converting 24fps material to NTSC framerates.

PAL uses the same interlacing technology as NTSC. They just have different framerates and color encoding. Therefore, PAL material is encoded as interlaced: because each full frame equals each frame of film doesn't make it progressive.

What’s the internal temperature of a TaunTaun? Luke warm.

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Mavimao, thanks for your reply. However, I'm not confused between interlacing and 3:2 pulldown, I just want to know how those 25fps become 29.97fps.
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OK, sorry to sound condecending! :-)

But I don't know that answer. The simple answer would be that they slow it down to 24fps and then do a pulldown....

Let's google.

What’s the internal temperature of a TaunTaun? Luke warm.

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Originally posted by: Mavimao
The simple answer would be that they slow it down to 24fps and then do a pulldown....

Let's google.

I'm thinking along the lines of a real-world test, putting a PAL film disc in my portable DVD player and switching the output to NTSC, capturing the output on my PC and seeing if fields are repeated or blurred to turn 25p into 29.97i.
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***Citizen's NTSC DVD/PAL DVD/XviD Info and Feedback Thread***
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Originally posted by: Mavimao
The simple answer would be that they slow it down to 24fps and then do a pulldown....
Yes, that's what I was thinking when this question began, but then Citizen said that PAL discs play at PAL speed, not true speed. Let me know what you come up with if you do that test, Citizen.
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Originally posted by: Darth Editous
Bit off-topic, but whenever I use AVISynth the result is always darker than the input. Anyone else noticed this, or found a way around it?


If you are using Avisynth for frame rate conversion, there is no change to the composition of the frames, but if using it for smoothing and other functions, then yes, it can change the brightness etc as often this is due to the Y-C conversions done by some filters.

ntrprs