ADOBE PREMIERE PRO: Tutorials Forum Articles Creative Cloud Debate

Closed Caption issue on Timeline

COW Forums : Adobe Premiere Pro

<< PREVIOUS   •   FAQ   •   VIEW ALL   •   PRINT   •   NEXT >>
David Bowen
Closed Caption issue on Timeline
on Jul 8, 2020 at 5:32:10 pm

Hi Forums,

I am trying to pair .srt files with video on the timeline. Both .srt and video files are timed to 23.976 but there is significant drift in the captions -- at minute 20, the captions are six seconds late.

Does anyone know what might be causing this? According to the file descriptions, they are both 2398 so there should be no drift.

Any help is appreciated. Thanks!


Return to posts index

Blaise Douros
Re: Closed Caption issue on Timeline
on Jul 8, 2020 at 11:57:26 pm

Is the .srt timed to 23.976, or 23.98? If my math is right, a 23.98 .srt on a 23.976 timeline would have drift of 4.8 seconds over 20 minutes. If the .srt is reading as 23.98, try interpreting it as 23.976.


Return to posts index

Andy Ford
Re: Closed Caption issue on Timeline
on Jul 9, 2020 at 3:31:22 am

Blaise, as usual, seems to be on the right track here. Also, the difference in 23.98 vs 24fps over 20 minutes is exactly 1.2 seconds. This plus Blaise's 4.8 seconds equals your 6 second difference in 20 minutes. So let's double check the frame rate things are actually being played at (or interpolated at).

-------------------------------------------------
Video Producer / Digital Marketer / Reviewer / Author
http://www.AndyFordVideo.com
-------------------------------------------------


Return to posts index


Andreas Kiel
Re: Closed Caption issue on Timeline
on Jul 9, 2020 at 10:03:20 am

SRT is a time based format - not a frame based one.
Therefore there is no 23.98, 23.976, 23.976023976023976, 24, 25, 29.97 DF etc.
Time resolution is 1/1000 and should be timed at real world time and not NTSC time.
There is no difference between 23.98, 23.976 or 24/(1001/1000) - at least not with professional tools.

So PPro will interpret the SRT at a given frame rate for a given TC type for display TC - time doesn't change.

So Andy Ford is somehow correct to say the difference between real world time and NTSC time is about 1.2 seconds off - but that's displayed TC.
Means a "00:20:00:00" real world TC will be displayed as "00:19:58:19" NTSC, but that would only matter if you got a frame based source and it won't be "too late".

So your SRT is wrong.
If there of a 6 second off within 1200 seconds there is a 0.5 percent drift - that's severe

Spherico
http://www.spherico.com/filmtools

"He who fights with monsters should be careful lest he thereby
become a monster. And if thou gaze long into an abyss, the abyss will
also gaze into thee." - Friedrich Nietzsche, Beyond Good and Evil


Return to posts index

Andy Ford
Re: Closed Caption issue on Timeline
on Jul 9, 2020 at 4:22:58 pm

Good point, Andreas. I know you are well-versed in captioning, so a question I have off of this is as follows: SRT is not frame based, it's time based. But it was created based off a video. If that video is now playing at a slightly different rate based on the fact that it could be in a sequence with a slightly different frame rate, it seems that could make the captioning seem off. Is that possible? Or, is it always an error with the SRT file?

-------------------------------------------------
Video Producer / Digital Marketer / Reviewer / Author
http://www.AndyFordVideo.com
-------------------------------------------------


Return to posts index

Blaise Douros
Re: Closed Caption issue on Timeline
on Jul 9, 2020 at 7:53:52 pm

Andreas--you're right, I'd forgotten that quirk about .srt. Could the problem, then, simply be an improperly interpreted video file (i.e. the srt is "correct" but the video's framerate is the real problem)? If the video is 23.98, on a 23.976 sequence, perhaps the answer is to interpret the footage to 23.976.


Return to posts index


Andreas Kiel
Re: Closed Caption issue on Timeline
on Jul 10, 2020 at 11:56:11 am

Andy, Blaise,

It's difficult to give any analysis from the distance without seeing both SRT and video.
I can only guess how the SRT was created and have no idea which 'base video' with what application/service was used.

Andy's point could be a reason. As an example in PAL - or better Non-NTSC - world it is common practice to switch between 24 and 25 just by 'playing' the movie faster or slower for the other way round. Pitch has to be adjusted.

The calculation for the example:
Cinema 24 to broadcast 25 with the given 20 min we get
20 min -> 20 x 60 (s) -> 1200 (s)
1200 (s) x 24 (frames/s) -> 28800 (frames)
These will be played faster
28800 (frames) / 25 (frames/s) = 19.2 (min) or 1152 seconds
means an SRT sub at 00:20:00,000 will be way too late.

So in this case the movie's timing/duration has changed.
But if somebody would resample the movie from 24 to 25 the SRT sub at 00:20:00,000 will fit.
It still would fit if the movie is resampled to 50 or 29.97 DF - if the used software can handle.

NTSC makes it more complicated - especially with its drop modes.
23.976 or lets call it 24 NTSC displayed TC of 00:20:00:00 doesn't mean the 'wall clock time' is the same: 00:20:01:05.

Spherico
http://www.spherico.com/filmtools

"He who fights with monsters should be careful lest he thereby
become a monster. And if thou gaze long into an abyss, the abyss will
also gaze into thee." - Friedrich Nietzsche, Beyond Good and Evil


Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2020 CreativeCOW.net All Rights Reserved
[TOP]