Convert softsubbed MKV files into hardsubbed MP4 files for playback via Roku, low powered devices etc, keep all fonts intact.

hardsub.sh

#!/bin/sh
# HARDSUB.SH
# (c) 2014 Fredrick Brennan
# 
# Usage notes:
# This script requires that ~/.fonts is in your fontconfig path.
# This script also requires mkvmerge, realpath and ffmpeg to be installed. Only supports SSA subs and MKV files.
# Also note that this script can take a long time to run.
# Run as `hardsub.sh FILE_NAME`
# You should be able to delete the following created files after it is done: done_subtitles.ass and the entire contents of ~/.fonts/MKV
# They are not deleted automatically because you may want to use them again for a subsequent ffmpeg run

DIRECTORY=$HOME/.fonts/MKV
# Save $1 because `set` will overwrite it
VIDEO_FILE=`realpath "$1"`
OUTPUT=$2
WD=`pwd`
declare -a FONTS
declare -a SUBTITLES

# Create fonts directory
if [ ! -d "$DIRECTORY" ]; then
	mkdir "$DIRECTORY"
fi

if [ ! -f "$VIDEO_FILE" ]; then
	echo "Cannot read $VIDEO_FILE"
	exit 1
fi

if [ -z "$OUTPUT" ]; then
	echo "Warning: No output file specified, will use output.mp4"
	OUTPUT='output.mp4'
fi

# Use mkvmerge to get all our subtitles
MKVMERGE=`mkvmerge -i "$VIDEO_FILE"`

if [ $? -ne 0 ]; then
	echo "mkvmerge failed to run!"
	echo "$MKVMERGE"
	exit 1
fi

# Get the track IDs of our subtitles
while read LINE; do
	set $LINE

	# $LINE should look like:
	# $1    $2 $3 $4        $5
	# Track ID 3: subtitles (SubStationAlpha)

	if [ $1 = 'Track' ]; then
		if [ $4 = 'subtitles' ]; then
			TRACK_ID=${3//[!0-9]/}; 
			SUBTITLES+=("$TRACK_ID")
		fi
	fi

	# $LINE should look like:
	# $1         $2 $3 $4   $5                             $6   $7    $8     $9   $10  $11
	# Attachment ID 1: type 'application/x-truetype-font', size 58224 bytes, file name '9SALERNO.TTF'

	if [ $1 = 'Attachment' ]; then
		if [ $5 = "'application/x-truetype-font'," ]; then
			ATTACH_ID=${3//[!0-9]/}; 
			FONTS+=("$ATTACH_ID")
		fi
	fi
done <<< "$MKVMERGE"

if [ ${#SUBTITLES[@]} -eq 0 ]; then
	echo 'Error: File has no subtitles!'
	exit 1
fi

echo ${#SUBTITLES[@]} subtitle tracks found: ${SUBTITLES[*]}
echo ${#FONTS[@]} font attachments found: ${FONTS[*]}

#Extract all our subtitles
for i in ${SUBTITLES[@]}; do
	mkvextract tracks "$VIDEO_FILE" "$i":subtitles"$i".ass
done

#Combine all subtitles into one mega SSA file; just simple concatenation seems to work.
cat subtitles* > done_subtitles.ass

#Delete separate subtitle files
rm subtitles*

#Extract all our fonts
cd $DIRECTORY
mkvextract attachments "$VIDEO_FILE" ${FONTS[*]}
cd $WD

#Do it. You can edit this line to your liking.
echo Running this line: ffmpeg -i \""$VIDEO_FILE"\" -acodec copy -vcodec libx264 -report -qscale 0 -vf "ass=done_subtitles.ass" "$OUTPUT"
echo 

ffmpeg -i "$VIDEO_FILE" -acodec copy -vcodec libx264 -report -qscale 0 -vf "ass=done_subtitles.ass" "$OUTPUT"

exit 0