Resize videos to a fixed size with avconv

video-resize.sh

#!/bin/sh
#
# Resize videos to a given size.
# Depedencies: libav

debug() {
  echo "$@" >&2
}

to_num() { local NUM_STRING=$1
  echo $NUM_STRING |
    sed -e 's/t/kg/i;s/g/km/i;s/m/kk/i;s/k/*1000/ig;s/b//i' | bc
}

get_video_duration() { local VIDEO=$1
  avconv -i "$VIDEO" 2>&1 | 
    awk '/Duration/ {split($2,a,":");print a[1]*3600+a[2]*60+a[3]}'
}

resize_video() { local INPUT=$1 OUTPUT=$2; ESIZE=$3; shift 3;
  local AUDIO_RATE=128000
  local DURATION=$(get_video_duration "$INPUT")
  local SIZE=$(to_num $ESIZE)
  local VIDEO_RATE=$(echo "($SIZE * 8) / $DURATION - $AUDIO_RATE" | bc)
  
  if ! echo "$VIDEO_RATE < 0" | bc -l >/dev/null; then
    debug "Negative video rate. Increase file size"
    return 1
  else
    debug "Audio rate: $AUDIO_RATE - Video rate: $VIDEO_RATE"
    avconv -loglevel info -i "$INPUT" \
      -f mp4 -movflags frag_keyframe+empty_moov \
      -codec:v libx264 -b:v $VIDEO_RATE \
      -codec:a ac3 -b:a $AUDIO_RATE \
      "$@" -strict -2 -y "$OUTPUT"
  fi
}

# Main

if test $# -ne 3; then
  echo "Usage: video-resize INPUT_FILE OUTPUT_FILE OUTPUT_FILE_SIZE"
else
  resize_video "$@"
fi