Difference bet NTSC and PAL subs?

[kikker]

If I have an x264 or xvid encoded film at the normal 23.976 fps, and I pair it with either a NTSC- or PAL- ripped .srt or .sub, what is the outcome?

Must the PAL-ripped .srt be converted from 25 fps to 23.976 fps in subtitle workshop to be in sync? What must be done to the NTSC-ripped .srt to be in sync?

[manusse]

In srt files, the timings are given in absolute time. In sub files, they are given in frames.

There is a direct relationship between NTSC (59.97 fps) and 23.976 fps. The ratio is 2.5. So the NTSC srt subs may be used directly in my opinion because the movie total duration must be exactly the same in NTSC and in x264 23.976.

Regarding a PAL sub, it is being played at 50 Hz. So the movie is a bit accelerated (25/23.976). So you must convert your srt from 25fps to 23.976fps. The converted srt will have its last sub later than the original one.

Cheers
Manusse

[kikker]

OK, thanks for the explanation. So, if .srt subtitles are constrained by time stamps, then a PAL-ripped .srt would have to be slowed down a bit. But, if I have a .sub subtitle file, which is displayed according to the actual video frame number, then it wouldn't matter if the .sub were ripped from a NTSC disc or PAL disc, as both discs contain the same number of frames, correct?

[burfadel]

OK, thanks for the explanation. So, if .srt subtitles are constrained by time stamps, then a PAL-ripped .srt would have to be slowed down a bit. But, if I have a .sub subtitle file, which is displayed according to the actual video frame number, then it wouldn't matter if the .sub were ripped from a NTSC disc or PAL disc, as both discs contain the same number of frames, correct?

Wrong way around! Subtitles that use timestamps can be interchanged freely as they are based on the same thing! 20 minutes into the movie is the same point regardless of where its pal, ntsc etc. Subtitles that use frame number cannot be interchanged, as ntsc has a different number of frames per second than pal. The 'framestamps'! can be readjusted using the appropriate programme.

[manusse]

Subtitles that use timestamps can be interchanged freely as they are based on the same thing! 20 minutes into the movie is the same point regardless of where its pal, ntsc etc

Sorry but it is not true. Let me try to explain it below.

*PAL - A 24fps movie is played at 50Hz on a PAL system. So 1 hour of movie is 24 x 3600 = 86400 frames. Which are played at 50Hz (25 fps because it's interlaced) a bit faster: duration = 86400/25 = 3456 sec = 57 min 36 seconds.
*NTSC - The same 24fps movie is played at 60Hz on a PAL system using what's called 3-2 pulldown. The first frame is played during the first 3 fields, then the second during 2 fields.... 3-2-3-2. As 60/24 is 2.5, this playing scheme will lead to the same exact duration for the 24Hz movie and its 60 Hz version. If the movie is 24Hz and the system NTSC, (59.97) there is a 1000/1001 timing difference. In you case 23.976 and 59.97, the timings must be identical.

So this means that the srt files for NTSC and PAL are a bit different.

You can find well detailed explanations on the web like for example this one: http://www.paradiso-design.net/videostandards_en.html

Also, people in PAL/SECAM countries know very well that films that they see on TV are a few minutes shorter than when they see them at Theaters.

Cheer
Manusse

[burfadel]

Ah yes. but when I said 20 minutes into the movie, I didn't mean sitting there with a stopwatch and timing it 20 minutes in! The 20 minute timestamp on Pal or NTSC is in the same spot! Such that if you play it at twice the speed, the 20 minute timestamp is still at the 20 minute mark, you just get there twice as fast!

Now with a subtitle file that has its own timestamp it will become out of sync, ideally it would be linked to the timestamps of the video itself.

[kikker]

...which is precisely why the timestamps of a .SRT file ripped from a PAL disc are a bit shorter than those from a NTSC-disc to compensate for the slight difference in fps of the film, correct? Therefore, the 2 .srt files are NOT interchangeable when paired with a 23.976 encoded film - only the NTSC .srt will be timed accurately.

Also, for the same film, it would seem to me based on the above explanation that a NTSC-ripped .sub and a PAL-ripped .sub ARE indeed interchangeable for the 23.976 encoded xvid because they are based on the actual video frame number, which would be the same for both .sub files.

Does that sound correct to both of you? You two seem to be disagreeing regarding my second post above.

[manusse]

a NTSC-ripped .sub and a PAL-ripped .sub ARE indeed interchangeable for the 23.976 encoded xvid because they are based on the actual video frame number

I am not sure about that.

Because the frame number for the last frame of a 1 hour NTSC movie would be 3599 x 59.97=215832 whereas for PAL it will be 3455 (see above why) x 50 = 172750.

I didn't mean sitting there with a stopwatch and timing it 20 minutes in! The 20 minute timestamp on Pal or NTSC is in the same spot!
The time difference between a PAL srt and the AVI you will be playing will be in the same spot... but with a difference of 1/25*20*60=48 seconds. Maybe 48 seconds of difference doesn't hurt you when you watch a movie but for me it's a huge difference although it's in the same spot. No need for a stopwatch to notice it.

Cheers
Manusse