create_thumbnail.sh

#!/bin/bash
# run with two args:  first is input directory path and second is output directory path
function usage()
{
	echo 'usage:  '$(basename $0)': /path/to/input/ /path/to/output/'
	echo '--';
	echo 'this script explores the input file system and selectively makes proxy versions of its media files in the output file system';
	echo 'NOTE: both arguments must be usable directories';
	exit;
}

# sanity checks
if [ "$#" -ne 2 ];
then
	echo "ERROR:  two arguments are required";
	usage;
fi;

if [ ! -d "$1" -o ! -r "$1" ];
then
	echo "ERROR:  $1 is not a readable directory";
	usage;
fi;

if [ ! -d "$2" -o ! -w "$2" ];
then
	echo "ERROR:  $2 is not a writable directory";
	usage;
fi;

inDir="$1";
outDir="$2";

cd "$inDir";

OLDIFS=$IFS;
IFS=`echo -en '\n\b'`;

for i in `find . -type f | grep -i '\(mov\)$'` ;
do 
	newDir=`dirname "$i"`; # modify this if you want to include the basename of the input argument directory
	mkdir -p "$outDir/$newDir";

	for f in "$i"
	do
	medianSecs=`ffprobe $f 2>&1 | grep -i duration | tr -C '[0-9]' ' ' | awk '{print "("$1"\*3600 + "$2"\*60 + "$3")/2"}' | bc `;

	ffmpeg -i "$f" -ss "$medianSecs" -f image2 -vframes 1 "$outDir/$newDir/$(basename $i)".jpg;
	done;
	done;
IFS=$OLDIFS