auti-epub

#!/bin/sh

echo "welcome to auti-epub"

function usage {
    cat << USAGE
Usage auti-epub input-file [subtitles]

Examples:
    auti-epub my-file.mp4           Output 'my-file.epub'
    auti-epub my-file.mp4 subs.srt  Output 'my-file.epub' using subs.srt

Report bugs to <example@example.com>
USAGE
}

# >> Get input

input=$1
# TODO: Allow outside subtitle file
subs="$2"



# >> Check input

if [ "$input" == "" ]; then
    echo "Error: No input file"
    usage
    exit 1
fi



# >> Create temp folder

rm -r tmp 2> /dev/null
mkdir tmp



# >> Extract times to capture

echo "Extracting times to capture"

# No subtitle file provided, get it from the input file
if [ "$subs" == "" ]; then
    # TODO: Detect which stream is the subtitle stream (if needed)

    subs="tmp/subs.srt"
    # Extract the subtitles
    # https://superuser.com/a/927507
    ffmpeg -i $input -map 0:s:0 $subs 2> /dev/null
fi

# Extract the fps
# https://askubuntu.com/a/110269
fps="$(ffmpeg -i $input 2>&1 | sed -n "s/.*, \(.*\) fp.*/\1/p")"

# Parse times from the subtitles
# TODO: sort the subtitles by the sequence numver
# TODO: delete the first line if it's empty
# TODO: only look for the second line of a paragraph rather than grep
times="$(grep -oE '^([0-9]{2}:[0-9]{2}:[0-9]{2},[0-9]{3})' $subs)"

if [ "$times" == "" ]; then
    echo "error: there were no subtitles found"
    exit 1
fi

# Convert times to frames
function time_to_frames {
    fps=$1
    time=$2

    # parse time
    hours="${time:0:2}"
    hours="$((10#$hours))" # Convert to base 10 https://stackoverflow.com/a/24777667
    minutes="${time:3:2}"
    minutes="$((10#$minutes))"
    # Ignoring the milliseconds bit seems to work just fine
    seconds="${time:6:2}"
    seconds="$((10#$seconds))"
    seconds="$((seconds + 1))" # round up so we're in the bounds

    # Combine into seconds
    seconds="$(echo "($hours*60*60)+($minutes*60)+$seconds" | bc)"
    frame="$(echo "$seconds*$fps" | bc)"
    # Round up to the next frame
    # https://stackoverflow.com/a/32797696
    frame="$(echo "scale=0; ($frame+0.5)/1" | bc)"
    echo $frame
}



# >> Extract the frames w/ subtitles

echo "Extracting frames w/ subtitles"

# Create the ffmpeg select string
select_string=""
while IFS= read -r line; do
    frame="$(time_to_frames $fps $line)"
    select_string="$select_string+eq(n\,$frame)"
done <<< "$times"
select_string="${select_string:1}" # remove leading '+'

# Bake in subtitles
# TODO: Combine with extracting frames?
extension="${input##*.}"
subtitled="tmp/subtitled.$extension"
ffmpeg -i $input -vf subtitles=$subs $subtitled 2> /dev/null

# Extract frames
# https://stackoverflow.com/a/38259151
mkdir tmp/frames
ffmpeg -i $subtitled -vf subtitles=$subs -vf select="$select_string" -vsync 0 tmp/frames/%d.jpg 2> /dev/null



# >> Package it as an epub

echo "Packaging as an epub"

./jpeg2epub --title "${input%.*}" tmp/frames/*



# >> Cleanup

rm -r tmp