Subtitle positioning: help required!

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carl
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Subtitle positioning: help required!

Post by carl »

In recent versions of DCP-o-matic there have been some misunderstandings and bugs about the vertical positioning of subtitles. I'm working on some changes to fix these problems. If you make DCPs with subtitles it would be very much appreciated if you could test these changes.

I will post test builds of DCP-o-matic to try out. I am interested in whether subtitles are displayed in the correct position in DCP-o-matic, and on the cinema screen in DCPs made by DCP-o-matic.

There are also some test DCPs if that is easier for you to test.

Do post in this thread or let me know by email to carl@dcpomatic.com if you have any questions or bug reports.
Carsten
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Location: Germany

Re: Subtitle positioning: help required!

Post by Carsten »

I read about this issues on the forum, but as I rarely use subtitles, am not fluent in all aspects of typical problems. I understand it is mostly about positioning references.
As some of the errors with positioning may be small, I am wondering wether one could create a bitmap based positioning template that one could use to evaluate burn-in and timed text positioning. That is, create a background bitmap to be encoded as J2K, where the burn-in and timed text SHOULD go, and then see wether they actually go in the final DCP playout and compare e.g. DCP-o-matic player and various projectors. Guess it's easier to check positioning against a visual positioning template than against a non-dedicated background.
carl
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Re: Subtitle positioning: help required!

Post by carl »

That's a good idea!
HaroldHallikainen
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Re: Subtitle positioning: help required!

Post by HaroldHallikainen »

In the SMPTE tests, the main picture had a grid with lines every 5% (I think!). It was pretty easy to tell where the subtitle landed.
barber
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Joined: Fri Apr 15, 2016 4:03 pm

Re: Subtitle positioning: help required!

Post by barber »

Hi, I made a quick test following Carsten and Harold suggestions (didn't find the SMPTE test though) :
  1. I created a standard SMPTE xml subtitle (attached) with Arial, black border, 42pt, 7% height from bottom.
  2. I burned that file into a 2K Flat grid (attached) using easyDCP. That gives me a DCP with the "target" subtitles at the right place.
  3. Using DOM test build 8e72274 I made a VF of this DCP with the original sub and another OV with the sub re-burnt-in.
With Open subtitles :
DOM preview has a slight shift (zoom?) which remains the same when I resize the window : https://i.imgur.com/wMte8AD.jpg
The resulting VF DCP is OK on easyDCP Player : https://i.imgur.com/9DvS1ek.jpg
DOM Player shows the shift : https://i.imgur.com/q9yCZFh.jpg

With burnt-in subtitles :
The shift is visible in both easyDCP and DOM Player : https://i.imgur.com/salLTXa.jpg

Still have to check on our NEC (I would assume that the VF is OK there too) and with other alignment values.

Best,
Dan
Attachments
EMPTYGRID_2KFLAT.tif
EMPTYGRID_2KFLAT.tif (12.37 MiB) Viewed 3431 times
TestSub_SMPTE.xml
(1.35 KiB) Downloaded 405 times
Kewl
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Location: Montreal, Canada
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Re: Subtitle positioning: help required!

Post by Kewl »

Maybe it's related or not, but when making a DCP from a Blu-ray, PGS subtitles are not following the cropping set in the Content/Video tab. Adjustments have to be done in the Content/Timed text tab to match what is seen when watching the Blu-ray source.
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Capture d’écran, le 2023-02-20 à 12.57.36.png
Capture d’écran, le 2023-02-20 à 12.57.36.png (4.05 MiB) Viewed 3416 times
carl
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Re: Subtitle positioning: help required!

Post by carl »

Maybe it's related or not, but when making a DCP from a Blu-ray, PGS subtitles are not following the cropping set in the Content/Video tab. Adjustments have to be done in the Content/Timed text tab to match what is seen when watching the Blu-ray source.
Thanks for the note. I think that's separate to what I'm interested in here (the weird/wrong alignment of DCP subs) so I made a separate bug report.
carl
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Re: Subtitle positioning: help required!

Post by carl »

Hi, I made a quick test following Carsten and Harold suggestions (didn't find the SMPTE test though) :
Thank you very much! I'll investigate that small error. Is it possible to export a full-size single frame image showing the original subtitle in EasyDCP player?
carl
Site Admin
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Re: Subtitle positioning: help required!

Post by carl »

I added some test DCPs to the first message.
barber
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Joined: Fri Apr 15, 2016 4:03 pm

Re: Subtitle positioning: help required!

Post by barber »

carl wrote: Mon Feb 20, 2023 10:47 pm Thank you very much! I'll investigate that small error. Is it possible to export a full-size single frame image showing the original subtitle in EasyDCP player?
Here it is : https://gofile.io/d/6DsH1W
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