makesmaller.js

var fs = require('fs'), child_process = require('child_process');

var files = fs.readdirSync('.');
var largeFiles = files.filter(function(f) {
	// check if the extension of f is jpg, png, or jpeg
	if(['jpg','png','jpeg'].indexOf(f.split('.').slice(-1)[0].toLowerCase()) == -1)
		return false;

	// check that the file is greater than 600K
	var stat = fs.statSync(f);
	return !stat.isDirectory() && stat.size > 600000;
});

// format size for output purposes
function formatSize(fileSizeInBytes)
{
    var i = -1;
    var byteUnits = ['K', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y'];
    do {
        fileSizeInBytes = fileSizeInBytes / 1024;
        i++;
    } while (fileSizeInBytes > 1024);

    return Math.max(fileSizeInBytes, 0.1).toFixed(1) + byteUnits[i];
};

console.log('found ' + largeFiles.length + ' files');

var numCompleted = 0;
largeFiles.forEach(function(file) {

	var fileParts = file.split('.');
	var oldStat = fs.statSync(file);
	// the filename that the smaller file will be saved to
	var newFile = fileParts.slice(0, fileParts.length - 1).join('.') + '.jpg';

	// we use ffmpeg to resize
	child_process.exec(
		'ffmpeg -i "' + file + '" -vf scale=1000:-1 -y -q:v 2 "' + newFile + '"',
		{
			cwd: process.cwd()
		},
		function(err, stdout, stderr)
		{
			if(err)
				throw err;
			// print new size
			var newStat = fs.statSync(newFile);
			console.log(file + ' (' + formatSize(oldStat.size) + ') -> ' + newFile + ' (' +  formatSize(newStat.size) + ')');

			// if the new file is different from the old file (didn't replace old file), delete old file
			if(newFile.toLowerCase() != file.toLowerCase())
				fs.unlinkSync(file);

			// check if we've finished
			numCompleted++;
			if(numCompleted >= largeFiles.length)
			{
				console.log('done');
				process.exit(0);
			}
		}
	);
});