This script for converting all videos on your NAS, i use this script for converting video on my Synology NAS, This will recursively convert all your video

video_convert_recursive.php

<?php

/*
Created by @ibnux January 2015
Use with your own risk

This script for converting all videos on your NAS
i use this script for converting video on my Synology NAS
This will recursively convert all your video
put this in your home folder
use command : nohup php -f video_convert_recursive.php > /dev/null &
this will start command in background, and you can close SSH
*/

//-------Configuration---------

//Change path to your Video Folder
$path = "/volume1/video/";

//result file
$GLOBALS['toExt'] = "mp4";
//list of supported video file to convert to $toExt
$GLOBALS['supportedFiles'] = ",avi,wmv,mkv,mp4,mov,flv,asf,mpg,mpeg,rm,rmvb,m4v,";
//this will appended to video ex: myvideo.mp4 -> myvideo.converted.mp4
$GLOBALS['fileName'] = "converted";
//if you want to remove original video
$GLOBALS['removeOriginal'] = true;
//minimum file size to convert
$GLOBALS['minSize'] = 250000000;
/*
Read This
https://ffmpeg.org/ffmpeg.html
http://edoceo.com/cli/ffmpeg
http://mattofalltrades42.hubpages.com/hub/FFmpeg-Command-Line-Examples-Resizing-Encoding-Transcoding-and-Comparing-Videos
http://www.catswhocode.com/blog/19-ffmpeg-commands-for-all-needs
my configuration below is to rescale video to 320p and use bitrate 512k, video for smartphone.
*/
$GLOBALS['ffmpeg'] = "-maxrate 512k -b:v 512k -vf scale=-1:320";

//get Extension File
function getExtension($str) {
         $i = strrpos($str,".");
         if (!$i) { return ""; }
         $l = strlen($str) - $i;
         $ext = substr($str,$i+1,$l);
         return $ext;
 }

function scanFolder($PathFolder){
	$temp = opendir($PathFolder);
	while ($folder = readdir($temp)) {
		$path = $PathFolder.$folder;
		//check is folder or not, minimum filesize and is already converted
		$size = filesize($path);
		if (!is_dir($path) && 
				$size>$GLOBALS['minSize'] && 
				strpos($path,".".$GLOBALS['fileName'].".")===false) {
			$ext = getExtension($path);
			if(strpos($GLOBALS['supportedFiles'],strtolower($ext))===false){
				echo "NOT selected: ".$GLOBALS['supportedFiles']." $ext $path $size\r\n";
			}else
				convertVideos($path);
				
		}else if (!in_array($folder, array("..", ".")) && is_dir($path)) {
			//if found folder, scan again to sub folder
			scanFolder($path."/");
		}
	}
	closedir($temp);
}
function convertVideos($path){
	$ext = getExtension($path);
	//create target filename
	//dirname to get Folder path without filename
	//basename to get filename without folder path
	$target = dirname($path)."/".basename($path,$ext).$GLOBALS['fileName'].".".$GLOBALS['toExt'];
	$result = exec('ffmpeg -i "'.$path.'" '.$GLOBALS['ffmpeg'].' "'.$target.'"');
	echo $result."\n";
	if($GLOBALS['removeOriginal']){
		  //if file size converted file more than 1MB, remove original 
	  	if(file_exists($target) && filesize($target)>1000000){
	  		unlink($path);
	  	}
	}
}

scanFolder($path);