Bash script for reducing a file size of a video using ffmpeg to reduce bitrate

reduce_video_file_size.sh

#!/bin/bash

# Usage:
# ~$ sh reduce_video_file_size.sh [./input.mp4] [size mb] [./output.mp4]
# Parameters can be preset or set by providing none
# Input and output names must end with ".mp4"
# Can use Git Bash to run the script on Windows

display_help() {
  local FILE=`basename "$0"`

  echo ""
  echo "Usage: $FILE input_file target_size_mb [output_file=output.mp4]"
  exit 0
}

INPUT_FILE=$1
TARGET_SIZE_MB=$2
OUTPUT_FILE=$3

# Ask for input before validating
if [[ $INPUT_FILE == "" ]]; then
  read -p "Enter the input file name: " INPUT_FILE
fi

if [[ $TARGET_SIZE_MB == "" ]]; then
  read -p "Enter the target file size in MB: " TARGET_SIZE_MB
fi

if [[ $OUTPUT_FILE == "" ]]; then
  read -p "Enter the output file name: (output.mp4) " OUTPUT_FILE
fi

# Require input file name
if [[ $INPUT_FILE == "" ]]; then
  echo "Input file name missing"
  display_help
fi

# Require target size
if [[ $TARGET_SIZE_MB == "" || !($TARGET_SIZE_MB > 0) ]]; then
  echo "Target size has to be at least 1 MB"
  display_help
fi

# Set the default output file name
if [[ $OUTPUT_FILE == "" ]]; then
  OUTPUT_FILE="output.mp4"
fi

# Check if the input file exists
if [ ! -f $INPUT_FILE ]; then
  echo "Input file $INPUT_FILE not found"
  exit 0
fi

# Check if the file size is already below the target size
INPUT_FILE_SIZE_MB=$(($(wc -c < $INPUT_FILE) / 1000000))

if [ $INPUT_FILE_SIZE_MB -lt $TARGET_SIZE_MB ]; then
  echo "The file size is already below the target size"
  exit 0
fi

# Additional bitrate division to make sure the size is below the target
ADD_TO_DIVIDER=50

# Calculate the target bitrate
BITRATE="$(awk "BEGIN {print int($TARGET_SIZE_MB * 1024 * 1024 * 8 / $(ffprobe \
  -v error \
  -show_entries format=duration \
  -of default=noprint_wrappers=1:nokey=1 \
  "$INPUT_FILE" \
) / (1000 + $ADD_TO_DIVIDER))}")k"

# Custom 2pass log file prefix
PASSLOGFILE="$INPUT_FILE-pass"

# Do the resizing
echo "Working..."
ffmpeg -v error -y -i $INPUT_FILE -c:v libx264 -preset medium -b:v $BITRATE -pass 1 -passlogfile $PASSLOGFILE -c:a aac -b:a 128k -f mp4 /dev/null && \
ffmpeg -v error -i $INPUT_FILE -c:v libx264 -preset medium -b:v $BITRATE -pass 2 -passlogfile $PASSLOGFILE -c:a aac -b:a 128k $OUTPUT_FILE
echo "Done"

# Delete junk files 2pass creates - could not find a way to disable
if [ -f $PASSLOGFILE-0.log ]; then
  rm $PASSLOGFILE-0.log
fi

if [ -f $PASSLOGFILE-0.log.mbtree ]; then
  rm $PASSLOGFILE-0.log.mbtree
fi