Speed up an input video by a given factor (or 2x by default)

speedvid.sh

#!/bin/sh

# REQUIREMENTS
# ffmpeg (brew install ffmpeg)
#
# INSTALLATION
# 1. Put the file somewhere (e.g. ~/bin)
# 2. Add that folder to your $PATH in .zshrc or equivalent (e.g. export PATH="$HOME/bin:$PATH")
# 3. Run it (speedvid input.mp4)

# if -h or no arguments are provided, print help and exit
if [ "$1" = "-h" ] || [ "$#" -eq 0 ]; then
    echo "Usage: speedvid [options] [input_file] [output_file --optional]"
    echo "Example: speedvid video.mp4"
    echo "Options:"
    echo "  -h, --help      Show this help message and exit"
    echo "  -s, --speedup   Speedup factor (default: 2)"
    exit 0
fi

# if -s or --speedup is provided, set speedup factor
if [ "$1" = "-s" ] || [ "$1" = "--speedup" ]; then
    speedup="$2"
    shift 2
else
    speedup=2
fi

# get the inverse of the speedup factor (for ffmpeg)
inv_speedup=$(echo "1/$speedup" | bc -l)

# if only -s or --speedup is provided, print error and exit
if [ "$#" -eq 0 ]; then
    echo "Error: no file provided (try -h or --help for help)"
    exit 1
fi

# get the file name
filename="$1"
shift 1

# get the filename without the extension
filename_without_extension="${filename%.*}"

# if there is an outfile, get that too
if [ "$#" -eq 1 ]; then
    outfile="$1"
    shift 1
else
    outfile="${filename_without_extension}-@${speedup}x.mp4"
fi

# speed up the video
ffmpeg -i $filename -filter:v "setpts=$inv_speedup*PTS" $outfile