regex for detecting subtitle errors - regex

Question

I'm having some issues with subtitles, I need a way to detect specific errors. I think regular expressions would help but need help figuring this one out. In this example of SRT formatted subtitle, line #13 ends at 00:01:10,130 and line #14 begins at 00:01:10:129.
13
00:01:05,549 --> 00:01:10,130
some text here.
14
00:01:10,129 --> 00:01:14,109
some other text here.
Problem is that next line can't begin before current one is over - embedding algorithm doesn't work when that happens. I need to check my SRT files and correct this manually, but looking for this manually in about 20 videos each an hour long just isn't an option. Specially since I need it 'yesterday' (:
Format for SRT subtitles is very specific:
XX
START --> END
TEXT
EMPTY LINE
[line number (digits)][new line character]
[start and end times in 00:00:00,000 format, separated by _space__minusSign__minusSign__greaterThenSign__space_][new line character]
[text - can be any character - letter, digit, punctuation sign.. pretty much anything][new line character]
[new line character]
I need to check if END time is greater then START time of the following subtitle. Help would be appreciated.
PS. I can work with Notepad++, Eclipse (Aptana), python or javascript...

Answer 1

Regular expressions can be used to achieve what you want, that being said, they can't do it on their own. Regular expressions are used for matching patterns and not numerical ranges.
If I where you, what I would do would be as following:
Parse the file and place the start-end time in one data structure (call it DS_A) and the text in another (call it DS_B).
Sort DS_A in ascending order. This should guarantee that you will not have overlapping ranges. (This previous SO post should point you in the right direction).
Iterate over and write the following in your file:j DS_A[i] --> DS_A[i + 1] <newline> DS_B[j] where i is a loop counter for DS_A and j is a loop counter for DS_B.

Answer 2

I ended up writing short script to fix this. here it is:
# -*- coding: utf-8 -*-
from datetime import datetime
import getopt, re, sys
count = 0
def fix_srt(inputfile):
global count
parsed_file, errors_file = '', ''
try:
with open( inputfile , 'r') as f:
srt_file = f.read()
parsed_file, errors_file = parse_srt(srt_file)
except:
pass
finally:
outputfile1 = ''.join( inputfile.split('.')[:-1] ) + '_fixed.srt'
outputfile2 = ''.join( inputfile.split('.')[:-1] ) + '_error.srt'
with open( outputfile1 , 'w') as f:
f.write(parsed_file)
with open( outputfile2 , 'w') as f:
f.write(errors_file)
print 'Detected %s errors in "%s". Fixed file saved as "%s"
(Errors only as "%s").' % ( count, inputfile, outputfile1, outputfile2 )
previous_end_time = datetime.strptime("00:00:00,000", "%H:%M:%S,%f")
def parse_times(times):
global previous_end_time
global count
_error = False
_times = []
for time_code in times:
t = datetime.strptime(time_code, "%H:%M:%S,%f")
_times.append(t)
if _times[0] < previous_end_time:
_times[0] = previous_end_time
count += 1
_error = True
previous_end_time = _times[1]
_times[0] = _times[0].strftime("%H:%M:%S,%f")[:12]
_times[1] = _times[1].strftime("%H:%M:%S,%f")[:12]
return _times, _error
def parse_srt(srt_file):
parsed_srt = []
parsed_err = []
for srt_group in re.sub('\r\n', '\n', srt_file).split('\n\n'):
lines = srt_group.split('\n')
if len(lines) >= 3:
times = lines[1].split(' --> ')
correct_times, error = parse_times(times)
if error:
clean_text = map( lambda x: x.strip(' '), lines[2:] )
srt_group = lines[0].strip(' ') + '\n' + ' --> '.join( correct_times ) + '\n' + '\n'.join( clean_text )
parsed_err.append( srt_group )
parsed_srt.append( srt_group )
return '\r\n'.join( parsed_srt ), '\r\n'.join( parsed_err )
def main(argv):
inputfile = None
try:
options, arguments = getopt.getopt(argv, "hi:", ["input="])
except:
print 'Usage: test.py -i <input file>'
for o, a in options:
if o == '-h':
print 'Usage: test.py -i <input file>'
sys.exit()
elif o in ['-i', '--input']:
inputfile = a
fix_srt(inputfile)
if __name__ == '__main__':
main( sys.argv[1:] )
If someone needs it save the code as srtfix.py, for example, and use it from command line:
python srtfix.py -i "my srt subtitle.srt"
I was lazy and used datetime module to process timecodes, so not sure script will work for subtitles longer then 24h (: I'm also not sure when miliseconds were added to Python's datetime module, I'm using version 2.7.5; it's possible script won't work on earlier versions because of this...