#!/bin/sh

if [ -z "$(command -v ffmpeg)" ]; then
    echo "ffmpeg required."
    exit
fi

_transcode ()
{
    ## Zsh compatibility. We need it otherwise word splitting of parameter like
    ## TC_SAMPLE will not work.
    STATUS="$(set -o | grep 'shwordsplit' | awk '{print $2}')"
    [ "$STATUS" = "off" ] && set -o shwordsplit

    ffmpeg -i "$@" \
        -c:v libx264 -preset slow -crf 20 \
        -c:a libvorbis -b:a 192k -ac 2 \
        -c:s copy \
        -map 0 \
        $TC_SAMPLE \
        "${1%.*}-$(date '+%F-%H%M%S').mkv"

    ## Restore Zsh previous options. This will not turn off shwordsplit if it
    ## was on before calling the function.
    [ "$STATUS" = "off" ] && set +o shwordsplit
}


_printhelp()
{
    cat <<EOF
Usage: ${1##*/} [-f] [FILES]

Transcode FILES using custom FFmpeg command.  By default FFmpeg will only encode
a sample for preview purpose. Use the '-f' flag to process the complete file.
Edit this file to fit your needs and learn more about FFmpeg.

EOF
}

TC_SAMPLE="-ss 60 -t 360"
while getopts ":hf" opt; do
    case $opt in
        h)
            _printhelp "$0"
            exit 1 ;;
        f)
            TC_SAMPLE="" ;;
        ?)
            _printhelp "$0"
            exit 1 ;;
        :)
            echo "Missing argument."
            _printhelp "$0"
            exit 1 ;;
    esac
done

shift $(($OPTIND - 1))

## Choose to process all files in one batch
_transcode ###FILELIST

## Or one after another.
# while read -r i; do
#     _transcode "$i"
# done<<FILELINES
# FILELINES

################################################################################
## USE CASES
##
## Exchange stream 1 an 2 by first removing them, then reading them in the
## desired order.
##
##   -map -0:1 -map -0:2 -map 0:2 -map 0:1
##
## Change audio stream 1 title and remove audio stream 2 title:
##
##   -metadata:s:a:0 title="FR: OGG Stereo" -metadata:s:a:1 title=""
##
## Demux audio:
##   -vn -sn -c:a copy -map 0:1
##
## Dump audio to an ogg file:
##   -vn -c:a libvorbis -b:a 192k
##
## Add a delay to audio (assuming stream 0 is video and stream 1 is audio)
##   -i "$1" -itsoffset 0.300 -i "$1" -map 0:0 -map 1:1
##
## Concatenate files. See
## https://trac.ffmpeg.org/wiki/How%20to%20concatenate%20(join,%20merge)%20media%20files
## for more details
##
##   -filter_complex '[0:0] [0:1] [1:0] [1:1] concat=n=2:v=1:a=1 [v] [a]' -map '[v]' -map '[a]'
##
################################################################################

################################################################################
## SOUND
##
## You should consider mixing down audio to 2 channels with '-ac
## 2'. This greatly reduce file size and avoid any confusion for playback, which
## is often the case when converting DTS to any other format because DTS has
## embedded channel description which is not available in other formats.
################################################################################

################################################################################
## X264 OPTIONS
##
## x264 presets (-preset <preset>).
##   preset ~= speed and quality*size ~= 1/speed
##   ultrafast, superfast, veryfast, faster, fast, medium, slow, slower, veryslow, placebo
##   Recommended values: faster -- slow
##   slow is approx. two times slower than fast, and reduces the size by approx. 10%.
##
## x264 overall quality (-crf) is a logarithmic scale.
##   18 is near perfection.
##   22 is really good compression, while a bit more blurry than the original.
##   20 is a good compromise.
##
## x264 tuning (-tune <preset>).
##   Possible values: film, animation, grain, ...
##   See x264 --fullhelp.
##   No tuning by default.
##
## x264 options (-x264opts me=<value>).
##   Possible values: hex, umh...
##   me=umh is default.
################################################################################

################################################################################
## FALLACIOUS INPUT
##
## In general, FFmpeg is not so good at copying fallacious streams. Reecoding
## video and audio streams helps a lot.
##
## "Can't write packet with unknown timestamp"
##   Put '-fflags genpts' before the input command.
################################################################################

################################################################################
## MISC
## To check what fmmpeg supports:
##   $ ffmpeg -codecs
##   $ ffmpeg -formats
##
## Useful guides:
##   x264: http://ffmpeg.org/trac/ffmpeg/wiki/x264EncodingGuide
##   ID3 details: http://en.wikipedia.org/wiki/ID3
################################################################################