PAL to NTSC telecining

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Sharc
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PAL to NTSC telecining

Post by Sharc »

Converting 24 (23.976)fps film to 30 (29.97)fps NTSC is normally done with soft or hard-telecining 3:2 pulldown.
Is there a similar (standardized) conversion process (pulldown pattern) for 25 => 29.97fps? Or would one normally slowdown the 25p to 24p and apply standard 3:2 telecine (+stretch the audio accordingly)?
For mpeg2 we could convert 25 => 29.97 with DGpulldown (soft pulldown or subsequent hard-encode), a similar tool does however not exist for AVC/mpeg4 as far as I know.
I am aware that the issue is probably no longer very relavant, as most (all?) AVC players will handle 25fps footage directly. Nevertheless one still finds ugly (field) blended or poorly interpolated crap from "PAL => NTSC" conversions.
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admin
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Re: PAL to NTSC telecining

Post by admin »

It would not be very difficult to make a DGPulldown for AVC (I already have a utility DGAVCPulldown that does pure 3:2). I am not aware of any implementation. It's hard to get excited about doing it. Lacking that, the slowdown trick you mentioned is the way to go if you must have NTSC.
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Sharc
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Re: PAL to NTSC telecining

Post by Sharc »

I will take the slowdown route, no problem. Good to know that there is no simpler or better way of doing it.
And it would definitely not make much sense to put efforts in a new tool which hardly anyone would use.
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Re: PAL to NTSC telecining

Post by admin »

Sharc wrote:And it would definitely not make much sense to put efforts in a new tool which hardly anyone would use.
Great minds...
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Aleron Ives
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Re: PAL to NTSC telecining

Post by Aleron Ives »

I actually encountered the "other" way of doing it some years ago. You can tell it's not very common, because mkvtoolnix wasn't able to handle it properly by default, but Moritz Bunkus was able to fix the bug after I reported it to him. What you do is slow 25 fps down to 25000 / 10001 (24.975) fps, then add one duplicate frame every 5 frames, so if your normal frame pattern is a b c d e f g h i j, you change it to a b c d e a f g h i j f. A normal second contains 25 frames, but by duplicating every 5th frame, you convert to 30 (~29.97) fps. Using DG's tools, you can convert a 29.97 fps clip back to 24.975 fps this way:

Code: Select all

Telecide(guide=3,post=2,vthresh=180)
Decimate(cycle=6)
Pattern guidance is optional, and you'll need to adjust the vthresh for your clip, of course.

This is IMO the better way to do the conversion, because slowing the clip from 25 -> 24 fps creates a much larger pitch shift in the audio that is more likely to be audible than the pitch shift caused by going from 25 -> 24.975 fps. The tradeoff is that you'll still get smooth motion by slowing the clip, whereas using duplicate frames will create judder that didn't exist in the original video. As always, YMMV.
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Re: PAL to NTSC telecining

Post by admin »

For sure it's an option. However, judder from frame repeats is very conspicuous. Is it worse than an audio slow-down? Choose your poison.
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Aleron Ives
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Re: PAL to NTSC telecining

Post by Aleron Ives »

Yep. The audio matter is more complicated these days, too. In the past you could usually assume that the audio had just been slowed down from 25 -> 24 fps, thus changing the pitch and tempo, so you could simply speed it up to 25 fps again to restore the pitch and tempo. These days it's possible to fix the pitch of an audio clip to compensate for tempo changes, so you can't tell if the audio just needs to be sped up again, or if you need to perform a second pitch correction to undo the first one. Without a reference clip, it can be impossible to tell what the correct processing method is. :wow:
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Sharc
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Re: PAL to NTSC telecining

Post by Sharc »

I tried the frame repeats option as well to minimize audio pitch shift. Although the judder is less for 6/5 (24.975=>29.97) than it would be for 5/4 (23.976=>29.97) it's still noticable for "PAL spoiled viewers" when playing it at 29.97. Possibly some smart HW players/TVs can restore the progressive sequence and display it at 24.975 (25), but as I am not sure what options and settings are available for my relatives in NTSC country I preferred the slowdown with 2:3 telecining option to minimize the judder. In my case the original audio is natively 25 fps (from my videocam) so I am comfortable with the 1 x pitch shift which can be compensated.
Thanks for sharing experience.
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Re: PAL to NTSC telecining

Post by admin »

Hey Sharc, a bit OT but great work supporting pinterf with testing on Avisynth+. Great contribution to the video community. :hat:
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jpsdr
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Re: PAL to NTSC telecining

Post by jpsdr »

PAL telecine has always (or 99% of the time) been done by speeding 24fps to 25fps.
Living in a 25fps country for several decades, i've never been bothered by all the "speeded" film i've watched on TV at the old times.
The reason is that the pitch is only noticeable in relative, not asbolute. I mean :
If you speed to much, when you listen, you imediately notice it's speeded up.
if you speed very few, you even don't notice difference with the original.
24 to 25 is intermediate. You'll notice the difference with the original, but if you don't listen to the original, you will not notice it.
Now, if your 25fps footage is already a telecine PAL, reduce to 24fps will give you the original speed.
If original speed is 25fps, the basic "and one frame each 5 frame" and after reduce to 29.97 will produce the same default than 3:2 pulldown : stuttering on... (never know the english world for "traveling".... argh).
As far as i know, the audio part of the PAL telecine was never "pitch corrected", the audio was just speeded up.
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Sharc
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Re: PAL to NTSC telecining

Post by Sharc »

Yes, I am familiar with the usual film-to-PAL (24 => 25) DVD speedup and pitch shift issues. (The speedup can be a godsend for certain movies, when it's a relief to finish watching a couple of minutes earlier...... ;) ) .
Pitch shift can be an annoyance though with concert DVDs, especially for the few people (not me) with an "absolute hearing" (I don't know the correct term in English).

In my case the native footage is 25 fps, and so is the audio. So I actually had to slowdown it to 23.976 and eventually apply audio pitch correction for the sensitive listener. Then apply 2:3 telecine to 29.97. No big deal, I was just wondering whether there exists a special (or standardized) telecine pulldown pattern for direct 25 => 29.97 (NTSC). Apparently not.

By the way, from the wiki for PAL to NTSC:
http://avisynth.nl/index.php/Interlacin ... nterlacing

Code: Select all

....
Video = SeparateFields (Video) # So that you may deal with the individual fields.
Video = SelectEvery (Video, 8, 0,1, 2,3,2, 4,5, 7,6,7) 
.....
Shouldn't this be
Video = SelectEvery (Video, 8, 0,1, 2,3,2, 5,4, 7,6,7) in order not to break the Top-Bottom sequence?
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Re: PAL to NTSC telecining

Post by admin »

Sharc wrote: Shouldn't this be
Video = SelectEvery (Video, 8, 0,1, 2,3,2, 5,4, 7,6,7) in order not to break the Top-Bottom sequence?
Seems you are correct. Well spotted!

This gives a ratio of 10 output fields per 8 input fields. That converts 25 to 31.25. Why wouldn't they use a correct ratio such as 12 per 10. I must be missing something. :scratch:
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Sharc
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Re: PAL to NTSC telecining

Post by Sharc »

admin wrote:
Sharc wrote: Shouldn't this be
Video = SelectEvery (Video, 8, 0,1, 2,3,2, 5,4, 7,6,7) in order not to break the Top-Bottom sequence?
Seems you are correct. Well spotted!

This is giving a ratio of 10 output fields per 8 input fields. That converts 25 to 31.25. Why wouldn't they use a correct ratio such as 12 per 10. I must be missing something. :scratch:
That's the standard 2:3 telecining which is used for converting 23.976 to 29.97 (or 24 to 30, or 25 to 31.5).
How would a 12 per 10 pulldown look like? Would the usual playback HW understand it and IVTC it correctly? :scratch:

Edit:
I'll try
Selectevery(10, 0,1, 2,3,2, 5,4, 7,6,7,8,9) and see how it plays back (2 combed + 4 progressive frames)
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Re: PAL to NTSC telecining

Post by admin »

The spec for repeat flag handling does not require that the pattern is 3:2 or any other fixed pattern. However, I don't know what players will do with the 6/5 pattern. Please let us know. Do these players even do IVTC with hard telecine?
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Sharc
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Re: PAL to NTSC telecining

Post by Sharc »

Hard-telecine 6/5 was exactly my concern. I'll run an encode and report back how it behaves ....

Edit:
Here some results:

PC: The 12/10 telecined stream can be perfectly IVTCed with script+PC, as expected. Audio adjustment is minimum 24.75/25=0.99 (1% slowdown only, same as mentioned by Aleron Ives for the frame repeat method). It's a bit of a surprise to me that this method has not gained more attention in the past compared to the usual 2:3 method (24 <=> 25) with much stronger audio adjust.

TV: When streaming the 12/10 hard-telecined file to my TV I noticed the pulldown judder, hence my TV does not do IVTC. I assume it is just bobbing the fields, possibly even in combination with some interpolation. Still, the judder is acceptable and definitely less annoying compared to the more simple frame repeat approach.

HW standalone players: I didn't do any tests, but for mpeg2/DVD I think to remember that there existed 2 classes of DVD players: Flag reading players doing IVTC based on the RFF/TFF flags (the vast majority I believe), and some (more expensive) cadence reading DVD players performing IVTC based on the discovery of the fields cadence, with a fallback mode to flag reading. I don't know (I have actually some doubts) whether the cadence reading players were capable to track anything else but the standard 2:3 cadence.

I think we have collected all practical options now. Thanks everyone for sharing ideas.
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Re: PAL to NTSC telecining

Post by admin »

Great information, Sharc! Thank you for your testing and analysis. Hopefully we are moving into an era of progressive video at a frame rate supported by all civilized nations.
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Aleron Ives
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Re: PAL to NTSC telecining

Post by Aleron Ives »

Unless you have to target DVD-Video as your output format, I don't think there's any reason to do any of this anymore. HDTVs support all framerates regardless of region, so if you have a Blu-ray player, you can just leave the video as 25 fps and burn it to a DVD-R in a MP4 or MKV container and play the stream without telecining it.
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Sharc
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Re: PAL to NTSC telecining

Post by Sharc »

Aleron Ives wrote:Unless you have to target DVD-Video as your output format, I don't think there's any reason to do any of this anymore. HDTVs support all framerates regardless of region, so if you have a Blu-ray player, you can just leave the video as 25 fps and burn it to a DVD-R in a MP4 or MKV container and play the stream without telecining it.
Basically yes, but I want to add a simple menu and therefore I author the files as a Blu-Ray disc / Blu-ray structure (or DVD in the past). I am aware that the Blu-ray standard includes 25p and 25i (with certain format restrictions), so I should actually be done with it. However, I learned to my very surprise that the support of 25/50 is optional for Blu-Ray standalones, and there seem to exist Blu-ray players which refuse to play 25fps footage even though it is Blu-ray compliant. I have not experienced this myself but there was a discussion about it in another forum (I still try to find it). So for my giveaways I decided to take the safe route and make it all "NTSC" compliant.
(The 25 fps player restriction is perhaps one reason why Blu-ray discs for sale in NTSC countries have original 25 fps productions always(?) converted to 23.976, 24 or 29.97. I have seen very ugly 29.97 converts with interpolation artefacts and blends which could have been avoided with pulldown techniques.)
Oh well, the PAL/NTSC heritage .....
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Aleron Ives
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Re: PAL to NTSC telecining

Post by Aleron Ives »

Yikes, thanks for that bit of information. I always buy the UK DVD/BD for PAL shows, because I'm not confident that the NTSC conversion will be handled properly, and I want the original video format, anyway. I wasn't sure if this was necessary for BD, because the standard should allow them to just use the PAL format for the North/South American release, but I've always played it safe and gotten UK BDs, because I can never find framerate information for BD releases to confirm that they're 25 fps. It seems I was right to be cautious and assume the people who author these discs don't know what they're doing. :wow:
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Sharc
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Re: PAL to NTSC telecining

Post by Sharc »

Doing some more research, I am not really convinced that 25/50fps support for Blu-ray is "mandatory in PAL regions only". It seems to be a quote from the "Blu-ray Demystified" book only, which is NOT a standard. But nevertheless, I would also recommended to avoid 'NTSC editions' of converted 25 fps PAL material. You can't be sure what you get. It's technically playable, but it can be very disappointing.
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jpsdr
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Re: PAL to NTSC telecining

Post by jpsdr »

Sharc wrote: Pitch shift can be an annoyance though with concert DVDs, especially for the few people (not me) with an "absolute hearing" (I don't know the correct term in English).
...
and eventually apply audio pitch correction for the sensitive listener.
I forgot to said that, yes, music can be the exception, when you perfectly know a music/song, you can notice the speedup even in absolute.

The few times i've tried pitch correction, the result was... "howfull", and you'll harm even more a sensitive listener.
But, it was a little time ago (several years), so maybe now it's better... :?:

Otherwise, i've personnaly authored 25p (576 and 1080) Blu-Ray tricking with "fake interlaced" when encoding, and it played on my standalone player perfectly.
After, i didn't try on others players, so...
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Sharc
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Re: PAL to NTSC telecining

Post by Sharc »

Finally (!) I found the document which made me believe that not all Blu-Ray players support 25 fps ("PAL"), and converting 25 to 29.97 ("NTSC") might still be advisable to be on the safe side, even in the global Blu-Ray age.

Search for example for "50Hz" in the document here (e.g. Para. 3.3.1, 3.3.2, 6.2.1):
http://www.blu-raydisc.com/assets/Downl ... -18780.pdf
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Aleron Ives
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Re: PAL to NTSC telecining

Post by Aleron Ives »

What about if you omit menus? BDMV has many arbitrary restrictions that don't apply to stand alone video files, e.g. the low consecutive B-frame cap.
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jpsdr
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Re: PAL to NTSC telecining

Post by jpsdr »

I've read indeed the document, it's... astonashing.
I mean, it's supposed to be a spec. Either a video format is supported, or it's not.
How can you have a spec with a format "wich may not be supported by all players"...?
It's totaly useless.
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Sharc
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Re: PAL to NTSC telecining

Post by Sharc »

No. It is NOT a spec. As the title says, it is just a White Paper (a tutorial if you like). That makes a huge difference.
I don't have access to the Blu-Ray spec. but I think to remember that it is a document of more than 1000 pages.
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