Subsync is a command line filter to synchronise the timeline of subtitles. It can shift, scale and non-linearly edit the timeline. It's simple, fast and easy to be integrated to Shell scripts. It supports .srt, .ass and .ssa formats. It's written in C and standard libraries so is able to be compiled in most of Posix systems like Linux, BSD, Cygwin, etc.
I had a couple of old TV shows and out-of-sync .srt files searched from websites. I knew the structure of .srt was quite simple so theoretically a small filter program can do the trick: filter out the time stamps, do some primary school-time mathematics, output back to the stream. To my surprise I couldn't find a command line tool to do it properly. Something were either too fancy with a heavy GUI interface, or too poor written by Shell scripts to do the basic calculation, especially to scale the timeline. Finally I decided to write one for my own needs. It might be reinventing the wheels. But come on, it costs only a handful hundred lines and a Sunday morning.
To install subsync, simply:
git clone https://github.com/xuminic/subsync.git
cd subsync
make
When successful, it will build the executable file subsync.
You may have it moved to anywhere accessible for you.
If no file was specified, subsync will read from stdin and write to stdout,
such as:
subsync +12000 < source.ass > target.ass
Otherwise it reads from the first non-option argument.
The output file can be specified by -w option.
For example, the above command is same to
subsync +12000 -w target.ass source.ass
Other options are:
- -c, --chop N:M
chop off the specified number of subtitles. You may use Vi to do the same thing.
- -o, --overwrite
overwrite the original file. It's useful in batch processing, but be wisely backing up your files before doing so.
- -r, --reorder [NUM]
reorder the serial number from NUM. It can be tidy up a little bit
when splitting or merging .srt files.
- -s, --span TIME
specifies the range of the time for processing. Used in non-linear editing.
- -w, --write FILENAME
specifies the output file.
- -/+OFFSET
specifies the offset of the timeline.
The prefix + or - defines postpone or bring forward.
It is defined by milliseconds like +19700, by HH:MM:SS.MS form,
such as -0:0:10,199, or by subtraction statement like
+01:44:31,660-01:44:36,290.
See "HOWTO: Shift Timeline".
- -SCALE
specifies the scaling ratio of the timeline.
It is defined by real number like 1.1988, by predefined identifiers
like N-P, or by dividing statement like -01:44:30,290/01:44:31,660.
The predefined identifiers are N-P which is same to 1.1988, P-N,
same to 0.83417, N-C, same to 1.25, C-N, same to 0.8, P-C, same
to 1.04271, and C-P, same to 0.95904.
See "HOWTO: Scale Timeline"
Timeline shifting means a fixed piece of time will be added up to, or taken away from the original time stamp in the subtitles. Timeline shifting is commonly used because most of the out-of-sync scenario were caused by the prefaces of different video sources.
For example, this command
subsync +12000 < source.ass > target.ass
will add 12000 milliseconds to all time stamps in source.ass, and pipe to the
new file target.ass, which is equal to delay all subtitles 12 seconds.
Whereas the + means add-up, the - would be read as taken-way, so
subsync -12000 < source.ass > target.ass
will bring forward all subtitles 12 seconds. The time stamp of offset can be an integer, which is in unit of millisecond, or a more readable form HH:MM:SS.MS which is also used in the subtitle files. For example:
subsync -00:10:07,570 source.ass > target.ass
To simplify the calculation, subsync supports subtraction statement
by the expected time stamp subtracting the misaligned time stamp.
For example, you randomly pick up a line of subtitle in the subtitle file.
The time stamp was written 0:11:00,140. It's the misaligned time stamp.
The corresponding line in the video actually sounds at 00:00:52,570.
It's the expected time stamp. You don't have to calculate the time difference
but simply using the formula expected-time-stamp - misaligned-time-stamp:
subsync +00:00:52,570-0:11:00,140 source.ass > target.ass
subsync will do the calculating itself.
Never mind the + character in the expression.
It's just an option switch. You may also use
subsync -00:00:52,570-0:11:00,140 source.ass > target.ass
because they are practically the same.
Note that there is a minor difference of the time stamps between .srt
and .ass. The .srt format is like 00:10:07,570, where the 570
after comma is milliseconds. On the other hand the .ass format is like
00:10:07.57, where the 57 after dot is in unit of 10 milliseconds.
Subsync accepts any of them.
In some scenario shifting timeline won't have it synchronised. You may find some videos had synchronised subtitle in the beginning but drifted away in the end. The offset can vary from seconds to minutes. It mostly caused by different frame rates. Such as your subtitle was ripped from a PAL based video but is about to match a NTSC video. Obviously the frame rate is 25 against 30 fps. Sometimes it became more subtle, like video was 24 fps but subtitle was 23.976. They are all practically 24 fps but you will find some seconds apart, which is quite annoying.
The cure is to scale the timeline, which is simply multiplying a ratio to every time stamps in the subtitle file. For example:
subsync -1.000955 source.ass > target.ass
When the ratio is greater than 1, the timeline prolongs.
When the ratio is less than 1, the timeline shortens.
The ratio is always a positive real number so here the - is
just a switch; +1.000955 do the same trick.
The ratio can be manually found by this formula:
expected-time-stamp / misaligned-time-stamp.
Assuming your video and subtitle are synchronised in the beginning,
but the last subtitle line, for example, was found 1:35:26,690.
Yet the scene was actually 01:35:32,160 so the subtitle was drifting forwards.
The expected time stamp is 01:35:32,160, equal to 5732160 milliseconds.
The misaligned time stamp is 1:35:26,690, equal to 5726690 milliseconds.
Therefore the ratio is 5732160 / 5726690 = 1.00095517655050299562,
where we only take 1.000955.
To simplify the calculation, subsync also supports dividing statement
by the formula expected-time-stamp / misaligned-time-stamp.
For example by the above arguments:
subsync -01:35:32,160/1:35:26,690 source.ass > target.ass
subsync will do the calculating itself.
Never mind the - character in the expression.
It's just an option switch. You may also use
subsync +01:35:32,160/1:35:26,690 source.ass > target.ass
because they are practically the same.
Subsync only supports limited non-linear editing. Sometimes the subtitle need both shifting and scaling. Sometimes only part of the subtitles need to be adjusted. In extreme situation you may have to use a subtitle editor. However if the situation is not that bad, subsync could speed up the process. Especially like the TV drama, once you figured out the formula of the first episode, it can be quickly applied to other episodes.
The timeline shifting and scaling can be combined in one command. The process order is shifting first, then scaling. Because the offset number is rather small so the error by multiplying the ratio can be ignored. The command line may look like this:
subsync +00:00:52,570-0:11:00,140 -01:35:32,160/1:35:26,690 source.ass > target.ass
Subsync supports a range to process. The option is
-s start-time-stamp [end-time-stamp]
The end-time-stamp is optional. The default is to the end of file if ignored.
For example:
subsync -s 0:01:15.00 1:23:34.00 -00:01:38,880-0:03:02.50 source.ass > target.ass
Which means starting from 1 minute 15 seconds, ending at 1 hour 23 minutes 34 seconds, all subtitle time stamp will be brought forward 83.62 seconds.
You may use Shell script to do the batch process, for example:
for i in *.srt; do subsync +12000 $i > $i.new; done
or by using -o option to override the original file so it looks neat:
subsync -o +12000 *.srt
Please keep in mind that backup your original files before the timeline were totally steins-gated.
The Chinese translation can be found at here.
The video length of EVA3.3 Theatrical Edition is 1:32:52. The subtitle file 00002.v1.11_FINAL.ass looked quite chaos. Looked into the file, the last line is
Dialogue: 0,1:45:42.51,1:45:46.48,Comment,,0,0,0,,♫Peace in time we've never had it so good\N安享和平 生活从未如此美好
which was 10 minute longer than the video.
By the way the 10 minute scene was about the story of 巨神兵.
Anyway found out the first meaningful talk at 00:00:52,570,
Tracking team, report current Eva unit positions.
The corresponding part in subtitle file is
Dialogue: 0,0:11:00.14,0:11:02.98,Default,,0,0,0,,追踪班 报告两机体现在的位置
Using subsync to calculate the difference:
$ subsync --help-sub 00:00:52,570 0:11:00.14
Time difference is -00:10:07,570 (-607570 ms)
Manually delete the 巨神兵 scene in the subtitle file first. Then
$ subsync -00:10:07,570 00002.v1.11_FINAL.ass > 001.ass
Tried this subtitle, it was sync-ed in the beginning then drafted away.
Apparently it was also needed scaling.
Went to the end part of the video, found the last talk at 01:35:32,160,
The Wunder streaks through the sky. The corresponding part in subtitle file is
Dialogue: 0,1:35:26.69,1:35:28.07,Default,,0,0,0,,划破天际的Wunder
Using subsync to calculate the scaling ratio:
$ subsync --help-div 01:35:32,160 1:35:26.69
Time scale factor is 1.000955
This ratio is very closed to 24/23.976, probably that's the reason of drifting.
Anyway using subsync process 001.ass again:
$ subsync -1.000955 001.ass > 002.ass
It works. I'd also tried with one command. The result was same.
subsync +00:00:52,570-0:11:00,140 -01:35:32,160/1:35:26,690 00002.v1.11_FINAL.ass > 002.ass
It's a 39 episode anime. All were out of sync. The video includes English subtitle
so it can be ripped out by ffmepg for reference:
ffmpeg -i "Nadia Ep 01.mkv" -map 0:s:0 subs.srt
The first subtitle was sync-ed:
1
00:00:03,200 --> 00:00:05,900
<font face="InfoDispBoldTf" size="46" color="#fffde1"><i>Are you adventurers,</i></font>
vs the ASS subtitle:
Dialogue: 0,0:00:03.50,0:00:05.50,*Default,,0000,0000,0000,,你是一位冒险家吗
However it went out of sync since No.18 lines:
18 00:01:09,630 --> 00:01:12,460 as the threat of a world war loomed ever closer.
19
00:01:38,880 --> 00:01:41,040
<font face="InfoDispBoldTf" size="46" color="#fffde1">Paris... Paris...</font>
vs the ASS subtitle:
Dialogue: 0,0:01:08.00,0:01:11.80,*Default,,0000,0000,0000,,但是人们生活在 即将来临的世界阴影中
Dialogue: 0,0:03:02.50,0:03:04.90,*Default,,0000,0000,0000,,巴黎…巴黎…
The video had only 30 seconds gap between No.18 and No.19. Yet the subtitle file had 2 minutes. Most likely contributed by different theme song. So tried it with subsync
subsync -s 0:01:15.00 -00:01:38,880-0:03:02.50 "Nadia Ep 01.ass" > 01.ass
The test was good, no need to scaling. However the first episode is different to
other episodes. The first scene only appeared in this episode so I had to process
another episode manually. From episode 2 the first 47 lines, which were 18 subtitle
lines, must be removed. The time difference was -00:00:01,710-00:01:25,510
so it can be done by
subsync -00:00:01,710-00:01:25,510 -r -o *.srt
The -r option was used to regenerate the serial number of SRT file.