Drop or Non_Drop Time Code

[sambat]

Before I start this project, I'd like to ask a general question about creating subtitles for an NTSC DVD (Master and Commander) from a 25fps .ssa file (using MaestroSBT).
In the 'Timing' setting I can elect 25.00 in and 29.97 out.
There is also a setting for 'Drop frame'.
Do I assume that since the DVD is 29.97 that it uses drop frame and output the applicable .sst file to use as input for MuxMan or is it a case of try one and if the timing of the subs is out, try the other.

[aedipuss]

by definition 29.97fps is "drop code". there is no such thing as "drop frame", as no frames are dropped when converting video time code to wall time code.

[edDV]

Can't speak to the rest but can explain drop/non drop timecode.

Video frames are not changed, only the time code. NTSC 29.97 video causes a ~4 sec difference over an hour. This causes problems in broadcast video which runs to a realtime clock. Drop frame time code allows precise insert of commercials and station breaks. If you don't care about sync to a clock, use non-drop-frame.

[manono]

Do I assume that since the DVD is 29.97 that it uses drop frame and output the applicable .sst file to use as input for MuxMan or is it a case of try one and if the timing of the subs is out, try the other.

First, don't assume that because the DVD outputs 29.97fps that you can do such a big framerate change as you're suggesting. Almost certainly you don't want to go from 25 to 29.97fps. If it's a film you've slowed to 23.976fps and are encoding with pulldown, do the slowdown before bringing it into MaestroSBT (using SubStation Alpha or Aegisub or whatever) and then set both input and output to 29.97fps and check the drop frame box.

If you're encoding for 25fps and then applying DGPulldown for 25->29.97fps, you leave it as 25 for both input and output (or 29.97 for both in and out, doesn't make any difference) and I think you also check the box. The reason I say 'think' is because I slow all my PAL sources to 23.976fps and don't mess with 25fps subs. But I might be wrong about that.

It should be easy enough to do a quick mux with Muxman and then check afterwards. That way you'll know for sure in the future. If the subs wind up about 7 seconds late by the end of a 2 hour long movie, then you should have left the box unchecked. Any difference greater than that and you did something much more seriously wrong (like setting 25fps for input and 29.97fps for output).

[manono]

by definition 29.97fps is "drop code". there is no such thing as "drop frame", as no frames are dropped when converting video time code to wall time code.

No frames are dropped, true, but there certainly is something known as drop_frame time code:

Don't get a wrong concept of DROP_FRAME as "FRAMES being REMOVED or DROPPED". In a 30fps Video sequence, a DROP_FRAME time code counts video frames accurately in relationship to real time. DROP_FRAME time code counts each video frame, but, when that .03 finally adds up to a video frame, it skips (or drops) a number. It does not drop a film or video frame, it merely skips a number and continues counting. This allows it to keep accurate time. So if you're cutting a scene using drop frame time code, and the duration reads as, say, 30 minutes and 0 frames, then you can be assured the duration is really 30 minutes. Confusing? Well, to put it in simple term, DROP_FRAME here is in essence EQUAL a SLOWED_DOWN playback from a pure 30fps into the correct NTSC 29.97fps SPEED. In an MPEG-2 domain, this means that the 00 and 01 frames are dropped or SKIPPED from time code, at the start of each minute except minutes which are even multiples of 10.
.
.
When the DROP_FRAME flag value is 1, it will ORDER the player to REMEMBER that the 00 and 01 frames are dropped at the start of each minute except minutes which are even multiples of 10. The result is much the same as applying the 29.97fps value.

http://www.doom9.org/synch.htm

[sambat]

Thank you all for your replies.

I won't be doing anything to the DVD video except demuxing with PgcEdit and muxing with MuxMan (to include a new, re-timed, subtitle).
The new subtitles are from a 25fps source and they will be re-timed to suit.
I was under the impression that the conversion from PAL to NTSC timing (strictly for the subpics) was to opt for 25-->29.97 and whether or not the drop frame box should be checked to further tweak the time (inasmuch as MaestroSBT offers the feature).

I don't suppose that there is a simple method of finding out if a source is using Drop or Non Drop timing?

[sambat]

Doesn't seem to matter about the Drop feature.
The converted subs times are not matching the dialog.
The closest is selecting 25 > 23.976 - but at only four and a half minutes into the movie the new subs are three seconds out.

English dialog 4:33

PAL SRT Sub 4:19
SST 29.97 Sub 3:36
SST 23.976 Sub 4:30

[manono]

OK, at 4 and a half minutes in they're that much off at 23.976fps. How are they at the beginning, at the first sub? How are they at the end? If it's the same three seconds, it's a simple matter of setting a delay in the SSA file.

You take a chance when trying to fit PAL subs to an NTSC DVD. The opening logos might have been different with the PAL DVD. It might have different scenes from the NTSC DVD.

I was under the impression that the conversion from PAL to NTSC timing (strictly for the subpics) was to opt for 25-->29.97...

Your impression was wrong. As you discovered, the 'base' framerate of NTSC movies is 23.976fps, and not 29.97fps. At the encoded 23.976fps and the displayed 29.97fps, the lengths are exactly the same, with 29.97fps being achieved by the addition of duplicated fields.

The new subtitles are from a 25fps source and they will be re-timed to suit.

As I said, I do the retiming before ever getting to MaestroSBT. Your way should work, if both DVD sources have exactly the same number of frames. Otherwise, you'll need either SubStationAlpha or Aegisub (or other programs if you're willing to convert to SRT and then later on back to SSA for MaestroSBT) to check out the timing as compared to the audio or a video file of the movie.

I don't suppose that there is a simple method of finding out if a source is using Drop or Non Drop timing?

Every subtitle I've ever worked with in MaestroSBT (roughly 1000) has required the box to be checked.

[sambat]

The time difference was the same for the start and end subtitles.
I used Subtitle Workshop to adjust the ssa file and generated a new sst file for muxman.
Found the time was still off, so I demuxed the closed captions and used it's settings for the first and last instead of guessing.
The result was better and after the colors were touched up with DVDSubEdit the movie was much easier to watch.
I didn't get anywhere using Drop_Frame, as soon as the box is checked it sets at 29.97 and the times are way off.
Thanks again for the helpful hints.

[manono]

I didn't get anywhere using Drop_Frame, as soon as the box is checked it sets at 29.97 and the times are way off.

Set both the In and the Out for 29.97. It's the same thing - the input framerate is the same as the output framerate.

[sambat]

Basically no difference in the times.



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