Script to run mplayer with two subtitles tracks at the same time. Usage: mplayer2 video sub1 sub2. merge2ass.sh (http://www.abclinuxu.cz/blog/Joseho_blog/2007/7/30/188299) script must be in the path.

merge2ass.sh

#!/bin/bash
# merge2ass.sh - script for merging two text-subtitles into an ass subtitle file
# version 0.9b, 02-feb-2013
# comments/criticism/praise to jose1711-gmail-com

# dependencies: mplayer (if your subtitle files need to be converted to srt), gnu utils

# thanks to:
#  - d.watzke for comments
#  - belisarivs for testing
#  - boris dušek <boris (dot) dusek - gmail - com> for testing/ideas
#  - swans100 - patch for milliseconds precision srt subs
#
# $1 is a movie file
# $2 is a subtitle1
# $3 is a subtitle2
# $4 is optional and could be "-pm" or "--play-movie" for instant watching of the movie

# example:
# merge2ass.sh movie.avi english.srt slovak.sub
# mplayer -noautosub -ass movie.avi -sub movie-bilingual.ass -subcp utf8
#
# or just
# merge2ass.sh movie.avi english.srt slovak.sub -pm
#
# or even only
# merge2ass.sh --detect movie.avi -pm
#
# 
#
# release history:
# 0.8a (29. 7. 2007)
#  - initial public release
# 0.8.1a (30. 7. 2007)
#  - check_syntax fixed (d.watzke)
#  - multiline echo -> cat (d.watzke)
#  - removes temp files after conversion
# 0.8.2 (1. 8. 2007)
#  - check whether the input files exist prior to running MPlayer
#  - check for MPlayer binary
#  - help page added
#  - new optional CLI parameters: -pm (plays movie after conversion), --help
# 0.8.2.1 (2. 8. 2007)
#  - timestamp in output more compatible (reported by belisarivs)
# 0.9 (8. 8. 2007)
#  - performs a check for writable output
#  - check for MPlayer's support of ass/ssa if -pm is used
#  - pointers to subtitle files stored as arraysF
#  - autorecognition of subtitles based on MPlayer's -sub-fuzziness feature (--detect)
#  - output filename based on movie filename (+bilingual.ass)
#  - bash now mandatory (non-POSIX syntax used)
#  - flag -pm has a long alias (--play-movie)
# 0.9a (27. 4. 2012)
#  - added compatibility with SRT subtitles using milliseconds precision (thanks juan!)
# 0.9b (2. 2. 2013)
#  - define encoding in ssa header (thanks mathieuu!)
#
# some future thoughts:
#   - more optional flags (do_not_remove_temp_files, play_but_dont_delete_output_afterwards,dont_do
#     the_conversion_just_merging,output_file..)
#   - cleaner sed/awk code
#   - support for other players (xine, totem, kmplayer, vlc..)
#   - subtitle encoding detection based on enca (if present) - boris?
#
# docs:
#   - http://en.wikipedia.org/wiki/SubStation_Alpha
#   - http://www.perlfu.co.uk/projects/asa/ass-specs.doc
#
# THE STORY ENDS HERE
# set -x

# normally you do not want to see mplayer's error output
#mplayer_err=/dev/stderr
mplayer_err=/dev/null

arg_count="$#"
movie="$1"
sub[1]="$2"
sub[2]="$3"


show_help(){
cat << EOF
 ----------------------------------------------------------------------------------
|                                                                                  |
|  Merge2ass - a script for merging two text subtitles into ass/ssa subtitle file  |
|                                         author: jose1711 - gmail - com, 2007/08  |
 ----------------------------------------------------------------------------------

  Usage: merge2ass.sh [--help] [movie subtitle1 subtitle2] [-pm|--play-movie]

         or

	 merge2ass.sh --detect movie [-pm|--play-movie]

--help        show this help page and exit

--detect      try to detect subtitles using MPlayer's sub-fuzziness=1 flag

movie         movie file (anything that MPlayer recognizes)
subtitle[12]  file(s) containing text subtitles that MPlayer recognizes 

-pm           play movie immediately and remove the output after finishing
--play-movie

EOF
}

detect_subtitles(){
	while read -r line; do
		sub[++i]="$line"
	done < <(mplayer -sub-fuzziness 1 -frames 0 "$movie" 2>/dev/null | sed -n "s/^SUB: Added subtitle file ([0-9]*): \(.*\)$/\1/p")
	echo "$i subtitles were detected in total."
	echo "These two will be used:"
	echo "${sub[1]}"
	echo "${sub[2]}"
}

convert_subs(){
type mplayer || { echo "MPlayer not installed or binary not in path, please investigate. Exiting.."; exit 1; } 

echo "Converting the 1st subtitle file (${sub[1]}) to a time-based format..."
# slower but does not require the video file for conversion
# mplayer /dev/zero -rawvideo pal:fps=25 -demuxer rawvideo -vc null -vo null -noframedrop -benchmark -sub "$movie" -dumpsrtsub
mplayer -dumpsrtsub -noautosub -really-quiet -frames 0 -sub "${sub[1]}" "$movie" 2>>"$mplayer_err" && echo "Done"
mv dumpsub.srt "${sub[1]}-temp"
echo "Converting the 2nd subtitle file (${sub[2]}) to a time-based format..."
mplayer -dumpsrtsub -noautosub -really-quiet -frames 0 -sub "${sub[2]}" "$movie" 2>>"$mplayer_err" && echo "Done"
mv dumpsub.srt "${sub[2]}-temp"
}

generate_ssa_header(){
cat > "$output" << EOF
[Script Info]
Title:
Original Script: 
Original Translation:
Original Editing: 
Original Timing: 
Original Script Checking:
ScriptType: v4.00
Collisions: Normal
PlayResY: 1024
PlayDepth: 0
Timer: 100,0000

[V4 Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, TertiaryColour, BackColour, Bold, Italic, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, AlphaLevel, Encoding
Style: lang1style,Arial,64,65535,65535,65535,-2147483640,-1,0,1,3,0,6,30,30,30,0,0
Style: lang2style,Arial,64,15724527,15724527,15724527,4144959,0,0,1,1,2,2,5,5,30,0,0
Encoding:0

[Events]
Format: Marked, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text 
EOF
}

generate_ssa_dialogs(){
sed -e "/ --> /s/,/./g" "${sub[1]}-temp" | tr -d "\r" | awk 'BEGIN{ORS="";print " "} / --> /,/^$/ {ORS=" ";print} /^$/{print "\n"}' | sed -e "s/ --> /,/g" -e "s/^ \([^ ]*\) \(.*\)/Dialogue: Marked=0,\1,lang1style,Cher,0000,0000,0000,,\2/" -e "s/,00:/,0:/g" -e "s/\([:,]\)0\([0-9]\)/\1\2/g" -e "s/\([0-9]\)\(\.\)\([0-9]\)\([0-9]\)0\(,\)/\1\2\3\4\5/g" >>"$output"
sed -e "/ --> /s/,/./g" "${sub[2]}-temp" | tr -d "\r" | awk 'BEGIN{ORS="";print " "} / --> /,/^$/ {ORS=" ";print} /^$/{print "\n"}' | sed -e "s/ --> /,/g" -e "s/^ \([^ ]*\) \(.*\)/Dialogue: Marked=0,\1,lang2style,Cher,0000,0000,0000,,\2/" -e "s/,00:/,0:/g" -e "s/^ *//g" -e "s/\([:,]\)0\([0-9]\)/\1\2/g" -e "s/\([0-9]\)\(\.\)\([0-9]\)\([0-9]\)0\(,\)/\1\2\3\4\5/g" >>"$output"
}

remove_temp_files(){
rm "${sub[1]}-temp" "${sub[2]}-temp"
}

play_movie(){
	mplayer -ass 2>/dev/null >/dev/null || { echo "Too old MPlayer version, can't understand ASS/SSA subs. Install a newer version."; exit 1; }
	mplayer -really-quiet -fs "$movie" -sub "$output" -ass -subcp utf8 -noautosub
}

delete_output(){
	rm "$output"
}

eval last_arg='$'${arg_count}

if [ $arg_count -eq 0 ]; then
	show_help
	exit 0
fi

for param in $*
do
	if [ $param = "--help" ]; then show_help; exit 0; fi
done

if [ "$movie" = "--detect" ]; then
	movie="${sub[1]}"
	output="${movie%.*}-bilingual.ass"
	> "$output" #|| { echo "Can't write here! Exiting.." && echo 1; }
	detect_subtitles
fi

if [ ! -f "$movie" ]; then echo "Movie file ($movie) does not exist. Going back to shell.."; exit 1; fi
if [ ! -f "${sub[1]}" ]; then echo "Subtitle1 file (${sub[1]}) does not exist. Going back to shell.."; exit 1; fi
if [ ! -f "${sub[2]}" ]; then echo "Subtitle2 file (${sub[2]}) does not exist. Going back to shell.."; exit 1; fi

echo "Processing.."
# reset output
output="${movie%.*}-bilingual.ass"
> "$output" #|| { echo "Can't write here! Exiting.." && echo 1; }

convert_subs
generate_ssa_header
generate_ssa_dialogs
remove_temp_files

if [ "$last_arg" = "-pm" -o "$last_arg" = "--play-movie" ]; then
	play_movie
	delete_output
fi

exit 0

# set +x

mplayer2

#!/bin/sh

if [ $# = 0 ]; then
   echo "Usage: mplayer2 movie sub1 sub2 [margin] [extra-params]"
   exit 0
fi

movie="$1"
extension=".${movie##*.}"
dirname=`dirname "$1"`

basename=`basename "$1" $extension`

sub_1="$2"
sub_2="$3"

if [ x${4} = x ]; then
   margin=0
else
   margin=$4
fi

if [ x${5} = x ]; then
   extra_params=''
else
   extra_params="$5"
fi


merge2ass.sh "$movie" "$sub_1" "$sub_2"
mplayer "$movie" -sub "${dirname}/${basename}-bilingual.ass" -ass -ass-use-margins -ass-bottom-margin $margin -ass-top-margin $margin $extra_params

It does not work under ubuntu 15.10 64 bit. It seems that mplayer do not generate dumpsub.srt.
merge2ass.sh outputs :
mplayer is /usr/bin/mplayer
Converting the 1st subtitle file (D.fra.srt) to a time-based format...
Done
mv: cannot stat ‘dumpsub.srt’: No such file or directory
Converting the 2nd subtitle file (D.eng.srt) to a time-based format...
Done
mv: cannot stat ‘dumpsub.srt’: No such file or directory
sed: can't read D.fra.srt-temp: No such file or directory
sed: can't read D.eng.srt-temp: No such file or directory
rm: cannot remove ‘D.fra.srt-temp’: No such file or directory
rm: cannot remove ‘D.eng.srt-temp’: No such file or directory