Simple script to adjust times for subtitles in SRT format

[puppy_apprentice]

I was showing some movies for my family on TV but noticed that subtitles aren't synchronized well with dialogs. So i've made a script:

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#!/bin/sh
# srted.sh by puppy_apprentice
# simple script to adjust times for subtitles in SRT format
# https://matroska.org/technical/specs/subtitles/srt.html
# usage: srted.sh srtfile delta skip

srtfile=$1 # file with subtitles in SRT format
delta=$2   # number of seconds
skip=$3    # start after subtitle number
n=1

# used grep for extra newline for read command
grep "" $srtfile | while read -r line
do
		if [[ $line =~ "-->" ]]
		then
			if [[ $n > $skip ]]
			then
				ft=$(date "+%s" -d "01/01/1970 ${line:0:8}")
				ft=$((ft+delta))
				st=$(date "+%s" -d "01/01/1970 ${line:17:8}")
				st=$((st+delta))
				line=${line/${line:0:8}/$(date +%T -d @$ft)}
				echo "${line/${line:17:8}/$(date +%T -d @$st)}"
			else
				echo "$line"
			fi
			n=$((n+1))
		else
			echo "$line"
		fi
done

Do we have in Puppy Land apps for subtitles editing/converting?

[MochiMoppel]

Doesn't seem to work properly with the srt sample of the matroska.org page

Sample srt text:

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1
00:02:17,440 --> 00:02:20,375
Senator, we're making
our final approach into Coruscant.

2
00:02:20,476 --> 00:02:22,501
Very good, Lieutenant.

With delta=2 and skip=0 it gives me this:

Code: Select all

1
00:02:19,440 --> 00:02:22,375
Senator, we're making
our final approach into Coruscant.

2
00:02:24,476 --> 00:02:22,501
Very good, Lieutenant.

Subtitle 1 is OK, subtitle 2 is not.

[puppy_apprentice]

LOL. For 10 movies and subtitles for them worked fine. I had luck

I think that switching two lines is enough:

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line=${line/${line:17:8}/$(date +%T -d @$st)}
echo "${line/${line:0:8}/$(date +%T -d @$ft)}"

Thx for feedback.

[MochiMoppel]

I also noticed that delta does not accept split seconds. I can imagine that even a delay of 0.5 sec can be annoying, so I tried a quick & dirty variation that allows deltas up to nanosecond level:

Code: Select all

#!/bin/bash
srtfile=$1 # file with subtitles in SRT format 
delta=$2   # number of seconds (min 1, max 9 decimals)
skip=$3    # start after subtitle number

[[ $delta =~ ^[0-9]*$ ]] && delta=${delta}.0	#date command requires delta to be floating-point value
n=1 

while read -r line || [ -n "$line" ] # reads last line even if it does not end with newline
do 
   if [[ $line =~ "-->" ]] 
   then 
	  if [[ $n > $skip ]] 
	  then 
		 ft=${line%% *}
		 st=${line##* }
		 echo "$(date -d"$ft +$delta sec" +"%T,%N") --> $(date -d"$st +$delta sec" +"%T,%N")"
	   else 
		 echo "$line" 
	  fi 
	  n=$((n+1)) 
   else 
	  echo "$line" 
   fi 
done < "$srtfile"

Previous example with delta=2.2 and skip=0 results in

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1
00:02:19,640000000 --> 00:02:22,575000000
Senator, we're making
our final approach into Coruscant.

2
00:02:22,676000000 --> 00:02:24,701000000
Very good, Lieutenant.

I'm not sure if the trailing zeros created by %N cause problems. If so we may trim them.

[puppy_apprentice]

I didn't test it on my TV or any Linux or Windows player, but i think that milli/nano seconds should be rounded to three places after the comma to be consistent with specification.

[Flash]

A nanosecond seems like overkill. Synchronized to within a millisecond will be sufficient for human ears.

[MochiMoppel]

A nanosecond seems like overkill. Synchronized to within a millisecond will be sufficient for human ears.

Human ears are not involved when it comes to subtitles. IMO even milliseconds are overkill and one digit should be sufficient. The date command displays fractions of a second always with 9 digits and there is no straightforward way to limit this number. Question is if the program processing the time value simply ignores excess zeros.

[Flash]

My mistake.

[MochiMoppel]

I didn't test it on my TV or any Linux or Windows player, but i think that milli/nano seconds should be rounded to three places after the comma to be consistent with specification.

Yes, rereading the spec it appears that exactly 3 digits are required.

Cutting instead of rounding should do:

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		 ft=${line%% *}
		 ft_new=$(date -d"$ft +$delta sec" +"%T,%N")
		 ft_new=${ft_new::12}	#cut to milliseconds
		 st=${line##* }
		 st_new=$(date -d"$st +$delta sec" +"%T,%N")
		 st_new=${st_new::12}	#cut to milliseconds
		 echo "$ft_new --> $st_new"

[misko_2083]

I didn't test it on my TV or any Linux or Windows player, but i think that milli/nano seconds should be rounded to three places after the comma to be consistent with specification.

Yes, rereading the spec it appears that exactly 3 digits are required.

Cutting instead of rounding should do:

Code: Select all

		 ft=${line%% *}
		 ft_new=$(date -d"$ft +$delta sec" +"%T,%N")
		 ft_new=${ft_new::12}	#cut to milliseconds
		 st=${line##* }
		 st_new=$(date -d"$st +$delta sec" +"%T,%N")
		 st_new=${st_new::12}	#cut to milliseconds
		 echo "$ft_new --> $st_new"

Or next

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date -d"$ft +$delta sec" +"%T,%3N" 

date +"%T.%3N" --> returns the current time with nanoseconds rounded to the first 3 digits, which is milliseconds.

[MochiMoppel]

date +"%T.%3N" --> returns the current time with nanoseconds rounded to the first 3 digits, which is milliseconds.

Great, thanks!
I've never seen this documented.

[puppy_apprentice]

So the final version is:

Code: Select all

#!/bin/sh
# srted.sh by puppy_apprentice, MochiMoppel, Flash and misko_2083
# simple script to adjust times for subtitles in SRT format
# https://matroska.org/technical/specs/subtitles/srt.html
# usage: srted.sh srtfile delta skip

srtfile=$1 # file with subtitles in SRT format
delta=$2   # number of seconds and/or miliseconds, format: S, 0.M, S.M
skip=$3    # start processing after subtitle number

[[ $delta =~ ^[0-9]*$ ]] && delta=${delta}.0   #date command requires delta to be floating-point value
n=1

while read -r line || [ -n "$line" ] # reads last line even if it does not end with newline
do
   if [[ $line =~ "-->" ]]
   then
     if [[ $n > $skip ]]
     then
       ft=${line%% *}
       st=${line##* }
       echo "$(date -d"$ft +$delta sec" +"%T,%3N") --> $(date -d"$st +$delta sec" +"%T,%3N")"
      else
       echo "$line"
     fi
     n=$((n+1))
   else
     echo "$line"
   fi
done < "$srtfile"

BTW Is it is possible to attach to GtkDialog window a video preview widget to make a visual subtitles maker?

[Flash]

Is it is possible to attach to GtkDialog window a video preview widget to make a visual subtitles maker?

Please start a new thread for this question. Otherwise, no one will ever see it. Thanks.