What is the subtitle frame rate when making a VF DCP?

[dhl]

Hello,

We're making VF DCPs for intentional distribution with local subtitles.

Our OV DCP is 24fps converted from the 23.97 master
Our VF subtitles file was made with the 23.97 master and is 23.97fps

What is the frame rate of our VF subtitle DCP if we use the 24fps DCP as OV? Does DOM automatically rate convert the VF file to match?

I ask because when I check subtitles in DOM and DOM player, I see perfect sync at the beginning, but if I stop and go later in the film, the subtitles are out of sync. I can't tell if this is the fault of DOM playback or if there is a sync issue. What is going on and how can I verify VF subtitle sync is correct?

Thanks for your help!
--David

[carl]

I think in your case you need to right-click on the subtitle file that you prepared for 23.97 and set "video frame rate that content was prepared for" to 23.97.

Once you made a 24fps DCP out of a 23.97 source you are running the video fast, so the subtitles must be sped up also. Most subtitle formats don't allow you to specify what rate they were prepared for, so DCP-o-matic just has to assume that the subtitles were prepared for the video that they are alongside.

This is all in theory, mind you, and it's a tricky area, so there could be bugs.

Having said all that, if you are seeing subtitle sync errors in the player I would be almost certain that it's a fault in the DCP.

[gunnar]

I ask because when I check subtitles in DOM and DOM player, I see perfect sync at the beginning, but if I stop and go later in the film, the subtitles are out of sync. I can't tell if this is the fault of DOM playback or if there is a sync issue. What is going on and how can I verify VF subtitle sync is correct?

This is a sync issue, just convert the subtitle to 24fps in a subtitle software and use that newly converted file for the VF.

[dhl]

I think in your case you need to right-click on the subtitle file that you prepared for 23.97 and set "video frame rate that content was prepared for" to 23.97.

Carl - Thank you. I set "video frame rate that content was prepared for" to 23.976 and made a new VF. Sync was perfect this time, both in DOM and the player.

Question - what's going on under the hood? I'm telling DOM that my subtitles are 23.97 but my OV is 24. How and where is the speedup of the subtitles happening?

This seems like an area where things could be clarified in UI. I assumed the the subs would be automatically converted to 24 like my source video was but I guess that's not the case without specifying the frame rate of the SRT first.

Thanks!
--David

[carl]

Carl - Thank you. I set "video frame rate that content was prepared for" to 23.976 and made a new VF. Sync was perfect this time, both in DOM and the player.

Great!

Question - what's going on under the hood? I'm telling DOM that my subtitles are 23.97 but my OV is 24. How and where is the speedup of the subtitles happening?

DCP-o-matic is adjusting them. As it converts from the time in the file to the time in the DCP it applies the required scaling.

This seems like an area where things could be clarified in UI. I assumed the the subs would be automatically converted to 24 like my source video was but I guess that's not the case without specifying the frame rate of the SRT first.

I'm certainly interested in suggestions for how to make this clearer. Though I can't see any way in which DCP-o-matic should know or guess that you have a 24fps video but have decided to import some 23.976fps subtitles. It might be worth having a dialog box on the import, perhaps...? At the moment if you import some image files it asks you what frame rate they are at, but with subs it just assumes they are the same as the video they are alongside.

[dhl]

It might be worth having a dialog box on the import, perhaps...? At the moment if you import some image files it asks you what frame rate they are at, but with subs it just assumes they are the same as the video they are alongside.

Yes, that sounds very reasonable to me, please consider it for a future version. In my case, subs were initially made for a BluRay release which is being made with the 23.97 master. We were asked to provide them for an international DCP and I forgot about the frame rate difference until my translator reminded me. In any event, I'm happy DOM does the right thing once it knows the SRT frame rate.

Thanks again for your help!

--David

[carl]

I will give it some thought, but it makes sense to me, at least today! Here's a note in the tracker.