merge.py

import argparse
from pysrt import SubRipFile, SubRipItem, SubRipTime

parser = argparse.ArgumentParser(description='Merge 2 srt files.')

parser.add_argument('fin', type=str, nargs=2,
                  help='input file')
parser.add_argument(dest='fout', type=str, nargs=1,
                  help='the output file')

args = parser.parse_args() 
master = args.fin[0]
slave = args.fin[1]
result = args.fout[0]

msubs = SubRipFile.open (master, encoding='iso-8859-1')
ssubs = SubRipFile.open (slave, encoding='iso-8859-1')
rsubs = SubRipFile.from_string ("", encoding='iso-8859-1')
tp = SubRipTime()

for msub in msubs:
   #"start before, ends before"
   for ssub in ssubs.slice (starts_after=tp, ends_before=msub.start):
       rsubs.append (SubRipItem(index=len(rsubs), start=ssub.start, end=ssub.end, text=ssub.text))
       ssubs.remove (ssub) # remove as completely handled.

   tp = msub.start

   #"start before; ends before end of master sub"
   for ssub in ssubs.slice (starts_before=msub.start, ends_after=msub.start):
       rsubs.append (SubRipItem(index=len(rsubs), start=ssub.start, end=msub.start, text=ssub.text))
       rsubs.append (SubRipItem(index=len(rsubs), start=msub.start, end=ssub.end, text=ssub.text))
       rsubs.append (SubRipItem(index=len(rsubs), start=msub.start, end=ssub.end, text=msub.text))        
       ssubs.remove (ssub) # remove as completely handled.
       tp = ssub.end

   #"start during; ends before master"
   for ssub in ssubs.slice (starts_after=msub.start, ends_before=msub.end):
       if (tp != ssub.start):
           rsubs.append (SubRipItem(index=len(rsubs), start=tp, end=ssub.start, text=msub.text))            
       rsubs.append (SubRipItem(index=len(rsubs), start=ssub.start, end=ssub.end, text=ssub.text))
       rsubs.append (SubRipItem(index=len(rsubs), start=ssub.start, end=ssub.end, text=msub.text))
       tp = ssub.end
       ssubs.remove (ssub) # remove as completely handled.

   #"start during; ends after master"
   for ssub in ssubs.slice (starts_before=msub.end, ends_after=msub.end):
       rsubs.append (SubRipItem(index=len(rsubs), start=ssub.start, end=msub.end, text=ssub.text))
       rsubs.append (SubRipItem(index=len(rsubs), start=msub.end,   end=ssub.end, text=ssub.text))
       rsubs.append (SubRipItem(index=len(rsubs), start=ssub.start, end=msub.end, text=msub.text))
       ssubs.remove (ssub) # remove as completely handled.
       tp = msub.end

   if (tp != msub.end):
       if (tp.ordinal < msub.start.ordinal):
           tp = msub.start
       rsubs.append (SubRipItem(index=len(rsubs), start=tp, end=msub.end, text=msub.text))
       tp = msub.end

rsubs.sort(key=lambda SubRipItem: SubRipItem.start.ordinal)

for idx, rsub in enumerate(rsubs):
   rsub.index = idx
rsubs.save (result, encoding='iso-8859-1')