Builds a montage from a video file, of a set length using equally spaced 1 second clips

montage-maker.sh

#!/bin/bash

# functions
function get_file_extension() {
   local filename=$(basename $1)  
   echo ${filename##*.}
}

function float_to_int() {
   echo ${1%.*}
}

function build_time() {
   local hours=$(expr $1 / 3600)
   local mins=$(expr $1 / 60)
   local secs=$(expr $1 % 60)
   
   echo "$hours:$mins:$secs"
}

# validation
if [ -z "$1" ]; then
   echo "$0 <input_file> <output_length> <output_file>"
   exit
fi

input_file=$1
output_length=$2
output_file=$3

file_type=$(get_file_extension $input_file)
input_length=$(float_to_int $(ffprobe -i $input_file -show_entries format=duration -v quiet -of csv="p=0"))

if [ $(expr $input_length '>' $output_length) -eq 0 ]; then
   echo 'output length greater than input length'
   exit
fi

# setup
workspace_name="workspace$RANDOM"
mkdir $workspace_name

# the time between each clip
time_fraction=$(expr $(expr $input_length - 1) / $output_length)

full_path=$(realpath $workspace_name)

# generating clips
for (( i=0; i<$output_length; i++ )); do
   time=$(build_time $(expr $time_fraction '*' $i))

   ffmpeg -loglevel panic -ss $time -i $input_file -t 00:00:01 -c:v copy -c:a copy $workspace_name/$i.$file_type

   echo "file '$full_path/$i.$file_type'" >> file_list
done

# concatenating clips
ffmpeg -loglevel panic -f concat -i file_list -c copy $output_file

# tear down
rm -r $workspace_name file_list