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Author Topic: Cross-conversion - 29.97 to 24fps  (Read 14654 times)

hdvprojection

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Cross-conversion - 29.97 to 24fps
« on: May 11, 2014, 03:39:36 AM »
Hello everyone. There is a theater I am regularly producing DCPs for which cannot play 30fps. The problem is obvious for anyone who's done a few of these: simply dropping frames looks awful if there are panning shots in them. But given how many young filmmakers come from TV, where everything is outputted at 29.97, it's a tricky business. The solution would seem to be cross-converting the source file to 23.98fps and then working from that. The question is, what's the best way to do that? Is there a basic command line solution in ffmpeg to get this done? TIA.

liloneum

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Re: Cross-conversion - 29.97 to 24fps
« Reply #1 on: May 30, 2014, 03:35:28 AM »
Hi,

Is your 29.97 fps source interlaced or not?

I am using -vf "fieldmatch=order=auto:combmatch=none, decimate" or -vf "fieldmatch=order=auto:combmatch=full, yadif=deint=interlaced, decimate" or -vf pullup -r 24000/1001

Never tried for HD source, just using to convert NTSC DVD to PAL.

Any feedback of your results are welcome.

hdvprojection

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Re: Cross-conversion - 29.97 to 24fps
« Reply #2 on: June 01, 2014, 04:33:47 AM »
Most of what I'm getting for source is progressive.

drmrr

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Re: Cross-conversion - 29.97 to 24fps
« Reply #3 on: June 02, 2014, 10:51:06 PM »
Any conversion is visible, be it blend or motion-compensated. Frameblending looks strange (but absolutely acceptable for documentary material) and motion-compensated conversion usually looks fantastic if you have the guts to go frame-by-frame through the entire feature to exclude all motion-prediction errors and artifacts (sometimes whole scenes look wrong).

Just shoot in 24p. Plain and simple. It looks nice on TV, too.

hdvprojection

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Re: Cross-conversion - 29.97 to 24fps
« Reply #4 on: June 03, 2014, 11:43:58 AM »
Any conversion is visible, be it blend or motion-compensated. Frameblending looks strange (but absolutely acceptable for documentary material) and motion-compensated conversion usually looks fantastic if you have the guts to go frame-by-frame through the entire feature to exclude all motion-prediction errors and artifacts (sometimes whole scenes look wrong).

Just shoot in 24p. Plain and simple. It looks nice on TV, too.

Yes and no. When my company has 29.97fps source files cross-converted by Fotokem, the resulting DCPs are fairly pristine. I guess my question is simply whether there is a way to do this without going to a lab. From what I can tell the process involves telecining/de-telecining 3/2 pull-downs. Not sure how that can be done with open source tools, if at all.

liloneum

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Re: Cross-conversion - 29.97 to 24fps
« Reply #5 on: June 03, 2014, 11:49:50 AM »
As far as I know, telecine / pulldown is a process to create interleaved 29.97 from progressive 23.976 (24 fps slower).
https://en.wikipedia.org/wiki/Telecine
ffmpeg can do the process with the video filters I mentioned for interleave source.
The results for SD source is perfect for my use.

In the case of progressive 29.97, each image has to be recalculated.

hdvprojection

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Re: Cross-conversion - 29.97 to 24fps
« Reply #6 on: June 03, 2014, 12:04:23 PM »
As far as I know, telecine / pulldown is a process to create interleaved 29.97 from progressive 23.976 (24 fps slower).
https://en.wikipedia.org/wiki/Telecine
ffmpeg can do the process with the video filters I mentioned for interleave source.
The results for SD source is perfect for my use.

In the case of progressive 29.97, each image has to be recalculated.

The best results I've been able to achieve thus far involved frame-blending with Adobe Premiere Pro. Still looks somewhat odd on panning shots, but much less headache inducing to watch than frame dropping. And it's not an option on my Linux machines, of course.

borjis

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Re: Cross-conversion - 29.97 to 24fps
« Reply #7 on: August 06, 2014, 05:29:48 PM »
I just had to deal with this issue.

We tried using premiere cc to do the 29.97 to 24.  It looked REALLY bad during wide panning vista shots.
So bad the producer and I both agreed this was unacceptable.

The solution was to pay to have it converted to 24 with a Terranex.  That made a HUGE improvement,
about 70% better.  any scenes with objects (cars or trucks for example) moving horizontally across
the scene were perfectly smooth.

The wide panning vista shots were much improved but a bit stuttery.

actpower

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Re: Cross-conversion - 29.97 to 24fps
« Reply #8 on: August 07, 2014, 04:10:22 AM »
Premiere pro donĀ“t make real Pulldown 3:2, as After Effects does.

Teranex is the best thing that you can use, and still cause artifacts.

Fix: make 30fps DCPs in SMPTE mode. It will be fail at some servers, but DCI want to push SMPTE mode to all cinemas, and I think is the way to go.

drmrr

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Re: Cross-conversion - 29.97 to 24fps
« Reply #9 on: August 07, 2014, 09:19:32 AM »
If the material initially was 24p (usually film-based) and then field-converted into 29.97i, this is called "3:2 pulldown" or "telecine". When you later reconvert the material to 24p, you are "removing the pulldown" or doing the "reverse telecine (IVTC)". This is how NTSC film transfers worked for many years. Outside of film-origination world the 3:2 pulldown is not of a much help.

If the material source is 29.97p (or 29.97i) (usually camera-based) and the frame-blending looks not good for you, you pay studio guys and they convert this for you using the motion-compensation process. Usually this involves hardware converters that are more (Shell & Wilcox's Alchemist) or less (For-A FRC or Blackmagic Teranex) sophisticated. Such hardware is expensive.

There are much cheaper software-only solutions (Twixtor is the most widely known) that are OK but even with careful tweaking you get some number of shots that exhibit motion artifacts like getting parts of the moving objects badly morphed or titles getting weid deformations. Most of those defects only last for a few frames so even without thorough manual fixing of the bad bits the converted material usually looks OK for projection 90% of the time.

Be prepared for long processing times (3 seconds per frame or so).

(Hardware converters also have problems with some shots but they are using post-processing to conceal the artifacts better.)

« Last Edit: August 07, 2014, 09:28:59 AM by drmrr »

Carsten

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Re: Cross-conversion - 29.97 to 24fps
« Reply #10 on: October 17, 2014, 03:01:30 PM »
Let's not forget that NTSC is actually 59,94 interlaced, and the telecine/pulldown process is based on interlaced signals to work properly. The inverse also works only if the source/intermediate signal is interlaced as well.

With progressive 29,97fps material, there is no other way than to use the best motion flow software or the teranex. 24/25fps to 29,97fps or the inverse is still the most challenging conversion in the media world, I suppose.

I would prefer all means to keep the footage on that frame rate, that means, conform to 30fps for DCP. For those few machines not supporting it, one could prepare a 24 fps version.

- Carsten


dcinemaforum.com

Re: Cross-conversion - 29.97 to 24fps
« Reply #10 on: October 17, 2014, 03:01:30 PM »