#!/bin/sh

## TODO: handle srt encoding?

_usage () {
	cat <<EOF
Usage: ${1##*/} [OPTIONS] FILES|FOLDERS

Transcode FILES or files found in FOLDERS to desired format (default to .mkv
with x264 and ogg vorbis). Black stripes are *not* cropped by default since it
may be sometimes inaccurate. By default output filenames are the same as the
original, with time appended.

Options:
  -a CODEC: Audio codec supported by ffmpeg. (Default: libvorbis).
  -b:       Default bitrate for audio stream with unidentifiable bitrate. If 0,
            copy stream (default).
  -c:       Copy streams (no reencoding).
  -C:       Enable auto-crop (needs video reencoding).
  -e EXT:   Set output container by specifying the extension. Defaults to mkv.
  -f:       Remove source when done.
  -h:       Display this help.
  -o OPT:   Additional options.
  -p:       Preview changes, do not encode.
  -P:       Generate two thumbnails, one cropped, the other not. Enable
            auto-crop, do not encode.
  -s:       Sample of 5 minutes.
  -S MIN:   Sample of MIN minutes.
  -t:       Remove all "title" metadata.
  -v CODEC: Video codec supported by ffmpeg. Defaults to libx264.

You can get a list of supported codecs with

  $ ffmpeg -codecs

User options are read from variable TC_VIDEO_OPT. This can be useful if you
often use the same options.

Examples:

* Get a preview of changes.

  ${1##*/} -p input.video

* Proceed with default options over folders and files.

  ${1##*/} input-folder input.video

* Convert to .avi container with xvid (quality 3) video and mp3 audio.

  ${1##*/} -e avi -v "libxvid -qscale:v 3" -a mp3 input.video

* Preview black stripes cropping.

  ${1##*/} -P input.video

* Process with default options and remove black stripes.

  ${1##*/} -C input.video

* Exchange stream 1 an 2 by first removing them, then reading them in the
  desired order.

  ${1##*/} -o '-map -0:1 -map -0:2 -map 0:2 -map 0:1' input.video

* Change audio stream 1 title and remove audio stream 2 title:

  ${1##*/} -o '-metadata:s:a:0 title="FR: OGG Stereo" -metadata:s:a:1 title=' input.video

EOF
}

EXT="mkv"
AUDIO_CODEC="libvorbis"
VIDEO_PARAM="-c:v libx264 -preset slow -crf 20"
AUDIO_PARAM=""

VIDEO_FILTER=""
AUDIO_DEFAULT_RATE=0

OVERWRITE="-n"
SAMPLE=""
OPT_OVERWRITE=false
OPT_REMOVE_TITLE=false
OPT_CROP=false
OPT_CROPPREVIEW=false
OPT_PREVIEW=false
OPT_COPY=false

while getopts ":a:b:cCe:fho:pPsS:tv:" opt; do
	case $opt in
	a)
		AUDIO_CODEC=$OPTARG ;;
	b)
		AUDIO_DEFAULT_RATE=$OPTARG ;;
	c)
		VIDEO_PARAM="-c:v copy"
		AUDIO_PARAM="-c:a copy"
		OPT_COPY=true;;
	C)
		OPT_CROP=true;;
	e)
		EXT=$OPTARG;;
	f)
		OVERWRITE="-y"
		OPT_OVERWRITE=true;;
	h)
		_usage "$0"
		exit 1 ;;
	o)
		TC_VIDEO_OPT="$OPTARG" ;;
	p)
		OPT_PREVIEW=true ;;
	P)
		OPT_CROP=true
		OPT_PREVIEW=true
		OPT_CROPPREVIEW=true ;;
	s)
		SAMPLE="-ss 60 -t 360" ;;
	S)
		SAMPLE="-ss 60 -t $((60*$OPTARG))" ;;
	t)
		OPT_REMOVE_TITLE=true ;;
	v)
		VIDEO_PARAM="-c:v $OPTARG" ;;
	\?)
		_usage "$0"
		exit 1 ;;
	esac
done

shift $(($OPTIND - 1))
if [ $# -eq 0 ]; then
	_usage "$0"
	exit
fi

if ! command -v ffmpeg >/dev/null; then
	echo "ffmpeg required."
	exit
fi

_highfreq() {
	awk 'BEGIN{max=0} /crop=/ {t[$NF]++; if (t[$NF]>max) {max=t[$NF]; val=$NF}} END{print val}'
}

## Usage: _cropvalue FILE STEP
## Return the crop values as ffmpeg output them.
_cropvalue() {
	local step=$2
	for i in $(seq $step $step $((5*$step))); do
		ffmpeg -nostdin -ss $i -i "$1"  -t 10 -vf "cropdetect=24:2:0" -f null - 2>&1
	done | _highfreq
}

## Return the audio encoding parameters. For instance
##   -c:2 libvorbis -b:2 384k -c:5 copy
## If input codec is $AUDIO_CODEC, we copy. If some stream bitrates are missing
## or 0, we encode it to a default value. If default value is 0, then we copy
## stream.
_audiobitrate() {
	local bitrate

	for i in $(seq 0 $(($format_nb_streams-1)) ); do
		## Skip non audio tracks.
		[ "$(eval echo \$streams_stream_${i}_codec_type)" != "audio" ] && continue

		bitrate=$(eval echo \$streams_stream_${i}_bit_rate)
		if [ -n "$bitrate" ] && [ "$bitrate" -gt 0 ] 2>/dev/null; then
			## If non-empty and a positive number.
			bitrate=$(( $bitrate / 1000))
		else
			bitrate="$AUDIO_DEFAULT_RATE"
		fi
		if [ "$bitrate" -le 0 ] || \
				 [ "$AUDIO_CODEC" = "$(eval echo \$streams_stream_${i}_codec_name)" ] || \
				 [ "$AUDIO_CODEC" = "lib$(eval echo \$streams_stream_${i}_codec_name)" ]; then
			printf -- "-c:%s copy " $i
		else
			[ $bitrate -gt 500 ] && bitrate=500
			printf -- "-c:%s %s -b:%s %sk " $i "$AUDIO_CODEC" $i "$bitrate"
		fi
	done
}

_transcode() {
	echo "==> [$1]"
	OUTPUT="${1%.*}.$EXT"
	[ -e "$OUTPUT" ] && OUTPUT="${1%.*}-$(date '+%F-%H%M%S').$EXT"

	## Metadata (i.e. tags + technical data).
	_buffer="$(ffprobe -v quiet -print_format flat=s=_ -show_streams -show_format "$1")"
	if [ $? -ne 0 ]; then
		_error "File [$1] is unsupported by FFmpeg."
		return
	fi
	eval "$_buffer"
	unset _buffer

	STREAM_TITLE=""
	if $OPT_REMOVE_TITLE; then
		for i in $(seq 0 $(($format_nb_streams-1)) ); do
			STREAM_TITLE="${STREAM_TITLE}-metadata:s:$i title= "
		done
	fi

	if $OPT_CROP; then
		echo "Computing crop values... "
		## For 5 different timeslices of 1 second at every 1/6th of the video,
		## we sample the crop values. We keep the values with highest
		## frequency. This is much faster than encoding in one pass with low
		## framerate.
		STEP=${format_duration:-$streams_stream_0_duration}
		STEP="${STEP%%.*}"
		STEP=$(($STEP/6))
		VIDEO_FILTER="-vf $(_cropvalue "$1" "$STEP")"
		if $OPT_CROPPREVIEW; then
			echo "Generating preview... "
			for i in $(seq  $STEP $STEP $((5*$STEP))); do
				ffmpeg -nostdin -v warning -y -ss $i -i "$1" \
					-f image2 -vframes 1 $VIDEO_FILTER "${1%.*}-preview-$i-cropped.png" \
					-f image2 -vframes 1 "${1%.*}-preview-$i-uncropped.png"
			done
		fi
	fi

	## WARNING: we mix 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 these formats.
	! $OPT_COPY && AUDIO_PARAM="$(_audiobitrate "$1") -ac 2"

	cat<<EOF
================================================================================
User options:  ${TC_VIDEO_OPT:-none}
Sample:        ${SAMPLE:-no}
Clear tags:    $OPT_REMOVE_TITLE
In place:      $OPT_OVERWRITE
Crop:          $OPT_CROP
Video codec:   $VIDEO_PARAM
Video filter:  $VIDEO_FILTER
Audio codec:   $AUDIO_PARAM
Output file:   $OUTPUT
================================================================================
EOF

	$OPT_PREVIEW && return

	ffmpeg -nostdin $OVERWRITE -i "$1" \
		$VIDEO_PARAM $VIDEO_FILTER \
		$AUDIO_PARAM \
		-c:s copy \
		-dn \
		-map 0 $STREAM_TITLE \
		$SAMPLE $TC_VIDEO_OPT "$OUTPUT"

	if $OPT_OVERWRITE; then
		rm "$1"
		mv -f "$OUTPUT" "${1%.*}.$EXT"
	fi
	echo
}

for i in "$@"; do

	## Argument is a folder. We search for all video files in there.
	if [ -d "$i" ]; then

		## WARNING: ffmpeg continues to read stdin once it has started, so it should
		## not be called from within a while<<EOF loop without disabling stdin.
		while IFS= read -r j; do
			_transcode "$j"
		done<<EOF
$(find "$i"  \( \
		-iname '*.avi' -o \
		-iname '*.flv' -o \
		-iname '*.mkv' -o \
		-iname '*.mov' -o \
		-iname '*.mp4' -o \
		-iname '*.mpeg' -o \
		-iname '*.mpg' -o \
		-iname '*.webm' -o \
		-iname '*.wmv' \) )
EOF

	else
		## Argument is a regular file.
		_transcode "$i"
	fi

done