gif2webm

#!/bin/bash
# convert *.gif file (and *.sfw and *flv) to *.webm
# resulting file is much smaller, though there will be more artifacts

FFMPEG="/usr/local/bin/ffmpeg"
let BITRATE=1024  # initial bitrate, may downgrade
AUDIO="-an"  # default is audio=null

if [ ! -x $FFMPEG ]; then echo >&2 "missing $FFMPEG"; exit 1; fi
F=$1
if [ ! -e "$F" ]; then
  echo >&2 "missing file: $F";
  exit 1;
fi
if [[ "$F" =~ .gif$ ]]; then
  G="${F/.gif/.webm}"
  let BITRATE=1024
  AUDIO=-an
elif [[ "$F" =~ .flv$ ]]; then
  G="${F/.flv/.webm}"
  let BITRATE=384
  AUDIO="-ac 1"
elif [[ "$F" =~ .swf$ ]]; then
  G="${F/.swf/.webm}"
  let BITRATE=384
  AUDIO="-ac 1"
else
  echo >&2 "not a a recognized format : $F";
  exit 1;
fi

OLDSIZE=$(stat -c%s "$F")
RATIO=100
while [[ RATIO -ge 100 ]]; do
  $FFMPEG -loglevel error -i "$F" $AUDIO -c:v libvpx -b:v ${BITRATE}K "$G"
  [ -e "$G" ] || break;
  NEWSIZE=$(stat -c%s "$G")
  RATIO=$(bc <<<"scale=0; $NEWSIZE * 100 / $OLDSIZE")
  if [[ RATIO -ge 100 ]]; then
    rm "$G"
    let BITRATE/=2
    if [[ BITRATE -lt 32 ]];then
      [ "$TERM" ] && echo "giving up; can't reasonably reduce file size";
      break;
    else
      [ "$TERM" ] && echo "bitrate ${BITRATE}K increased size to ${RATIO}%; trying again"
    fi
  fi
done
[[ -e "$G" ]] || exit 1;
[ "$TERM" ] && echo "$G reduced to ${RATIO}%"