#!/bin/bash -x

# usage: change-length.sh 1.007 input.mp4 output.mp4 [0] [--fast]
       
set -euo pipefail

RATIO=$1;
IN_FILE=$2;
OUT_FILE=$3;
IS_MAC=${4-"0"};
MODE=${5-"--slow"};
BITRATE=$(ffmpeg -i "$IN_FILE" 2>&1 | grep bitrate | awk -F", " '{print $3}' | sed 's/bitrate: //' | sed 's/ //' | sed 's/b\/s//' || echo "");

echo ratio set to "$RATIO"

INV_RATIO=$(python -c "print(1/$RATIO)");

FILTER="";
OPTS=();

AUDIO_FILTER="[0:a]atempo=$(echo "$INV_RATIO")[a]";

HAS_AUDIO=$( (ffprobe "$IN_FILE" || echo "") 2>&1 | grep Stream | grep --count Audio | tail -n 1);
HAS_VIDEO=$(ffprobe "$IN_FILE" 2>&1 | grep Stream | grep --count Video || echo "0");

slow () {
  echo " ";
  echo " ";
  echo " ";
  echo " ";
  echo "USING SLOW MODE. If you want only video, use --fast";
  echo " ";
  echo " ";
  echo " ";
  echo " ";
  echo " ";
  echo " ";
  echo " ";
  echo "Checking streams within the file...";

  if [ "$HAS_AUDIO" -ge 0 ]; then
    FILTER=$AUDIO_FILTER;
    OPTS+=(-map "[a]");
  fi;

  if [ "$HAS_VIDEO" -ge 0 ]; then 
    FILTER="$FILTER;[0:v]setpts=$RATIO*PTS,hwupload[v]";
    OPTS+=(-map "[v]");
  fi;

  echo "running with filter $FILTER";

  if [ "$IS_MAC" -eq 1 ]; then
    ffmpeg -hwaccel videotoolbox -i "$IN_FILE" -b:v $BITRATE -filter_complex "$FILTER" "${OPTS[@]}" -c:v h264_videotoolbox "$OUT_FILE";
  else
    ffmpeg -hwaccel vaapi -hwaccel_output_format vaapi -vaapi_device /dev/dri/renderD128 -i "$IN_FILE" -b:v $BITRATE -filter_complex "$FILTER" "${OPTS[@]}" -c:v h264_vaapi "$OUT_FILE";
  fi;
}

fast (){
  if [ "$HAS_AUDIO" -ge 0 ]; then
    TEMP_VIDEO="$(dirname $IN_FILE)/.temp.$(random).video.$(basename "$IN_FILE")";
    ffmpeg -itsscale "$RATIO" -i "$IN_FILE" -c copy -an "$TEMP_VIDEO";
    TEMP_AUDIO="$(dirname $IN_FILE)/.temp.$(random).audio.$(basename "$IN_FILE")";
    ffmpeg -i "$IN_FILE" -filter_complex "$AUDIO_FILTER" -vn -map "[a]" "$TEMP_AUDIO";
    ffmpeg -i "$TEMP_VIDEO" -i "$TEMP_AUDIO" -c:v copy -c:a copy "$OUT_FILE";
    rm -f "$TEMP_AUDIO" "$TEMP_VIDEO";
  else
    ffmpeg -itsscale "$RATIO" -i "$IN_FILE" -c copy -an "$OUT_FILE";
  fi;
}

if [ "$MODE" = "--fast" ]; then
  fast;
else
  slow
fi;