Category Archives: web development

Diving into Node.js – Very First App

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What do I have till now?

After Node.js is istalled, described in my previous post, I can simply run this command:

stoimenpopov:~# node server.js

and this will start the server with the code within server.js. But what’s the code of server.js?

Following the instructions of Node’s homepage and most of the tutorials I’ve found, I can simply copy/paste the code from the first lines of Node’s page:

var http = require('http');
http.createServer(function (req, res) {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World\n');
}).listen(8124, "127.0.0.1");
console.log('Server running at http://127.0.0.1:8124/');

There are several things I find interesting in this code, making it different from JavaScript as we know it. First of all what is

var http = require(‘http’)

and why I need it? What is the purpouse of 8124 and 127.0.0.1?

Node is built in modules and to use one of them you must first include it with require. Just like the example above with require(‘http’). In the same manner you can include every module of Node.

What are the Node’s modules are pretty well described in the API page. Well I’d like to say that the API page is quite insufficient. That is very bad, cause most of the code you’ll need developing a node.js applicatoin isn’t described/explained there. Continue reading Diving into Node.js – Very First App →

Diving into Node.js – Introduction & Installation

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Why I Need Something Like Node.js?

First of all the use of some software is needed not because of itself, but because of the need of some specific functionality. In my case this was the need of real time news feed. Of course there is a way to make this without Node.js, as I’ll describe later in this post, but there are several disadvantages. However to begin from somewhere, let me explain what is Node.js.

Introducing Node.js

Perhaps the best way do describe what is Node.js is from its about page.

Node’s goal is to provide an easy way to build scalable network programs. In the “hello world” web server example above, many client connections can be handled concurrently. Node tells the operating system (through epoll, kqueue, /dev/poll, or select) that it should be notified when a new connection is made, and then it goes to sleep. If someone new connects, then it executes the callback. Each connection is only a small heap allocation.

…

In general Node is a program using the Google Chrome’s V8 JavaScript engine, which in turn is a program that can parse and execute code written in JavaScript. V8 is a very very interesting project itself. First of all from Google have developed this engine especially for one of his products – their browser Chrome. It pretends to be and by no means is one of the masterpieces of Google. It is fast and reliable engine, written in C++ and JavaScript, as Wikipedia’s page says. Actually this code is open source and can be embedded in whatever application written in C++. Thus you can have in your application a JavaScript engine. Continue reading Diving into Node.js – Introduction & Installation →

How to Make MP4 Progressive with qt-faststart

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A big part of the developers worldwide, who have dealt with video converting, sooner or later have been used FFMPEG. In fact I’d say that two of the main software on the video converting scene are FFMPEG and Mencoder. I began to use Mencoder back in 2005 and I used it as a DVD ripping tool, but my experience with it ends there, while now I use FFMPEG.

However FFMPEG is a converting program and many things depend on what kind of video files come as an input and what do you want to achieve as an output. Here comes the codec question, where various libraries can help. In my case, as I wrote few posts ago, I use MP4 as output encoded with h.264, both encoded with ffmpeg/libx264. So far so good, but there is one main problem that anyone used this pair knows.

Flash Player and MP4

As far as I know Flash Player 9 and beyond plays video files encoded with MP4/h.264 except the typical FLV (flash video files). This can help video sites not only to share their video content via web – within browser based flash players, but also to show them via some mobile device interface where MP4/h.264 is perhaps the only one reasonable solution. In this case the file is accessible in both medias.

By default Flash Player can play such FFMPEG encoded .mp4 files, but fist the whole file must be downloaded by the browser and only than the playback can begin. That’s because the FFMPEG puts meta info at the end of the video file, while the flash player needs it at the beginning and only than to begin playing while the file is still downloading.

qt-faststart

As the name of this software says this program helps you move the important meta info from the end to the beginning of the file. This helps the video to playback as early as possible. In an ideal circumstances everything works just fine, but there is a serious problem in fact.

qt-faststart and Server Crash

qt-faststart is responsible to move the meta info where it must be – at the beginning of the video file, but cannot finish execution when the video file is broken or the meta info doesn’t exists. Actually this is not a problem of qt-faststart, but to the video file. However this was a critical problem in my case, because the video files remains stuck for hours of execution and 99% of CPU usage.

Thankfully there is a solution and it can be found in the qt-faststart wrapper – qtfaststart.py

qtfaststart.py

written on Python this script overcomes the disadvantages of qt-faststart. As described by his author Daniel G. Taylor:

  1. Works everywhere Python can be installed
  2. Handles both 32-bit (stco) and 64-bit (co64) atoms
  3. Handles any file where the mdat atom is before the moov atom
  4. Preserves the order of other atoms
  5. Can replace the original file (if given no output file)

With its help not only qt-faststart doesn’t crash, but also the video files remain progressive as desired. The installation process is as difficult as copy/paste on the server where Python must be installed.

ffmpeg, libx264 and presets

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When working with FFMPEG you can convert/encode in various formats, but in my case this should be an MP4 file, encoded with libx264. This combination is quite well known in the web community, because those videos are playable under almost any flash player and Apple products.

Now the problem is that this comes with very large list of options, which are difficult to setup, especially for newbies like me. Than everything’s difficult, once because the resulting quality is not always the same as the input file’s quality.

The Solution

Is to use presets. Thankfully ffmpeg with libx264 can be used with presets, i.e. NORMAL, HD etc. which means that you don’t have to setup a command by hand and the resulting quality is the same as the input quality.

Here’s a sample command using normal preset:

ffmpeg -i source.mp4 -acodec libfaac -ab 128k -ac 2 -vcodec libx264 -vpre normal -threads 0 -crf 22 output.mp4

here the source can be either mp4 or some other file format as FLV for instance.

Construct a Sorted PHP Linked List

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This is really a draft, but I somehow decided to post it. Here’s a simple linked list in PHP, where only the add() method is slightly different. When you have an item to add it’s placed on the “right” place – the result is a sorted list.

Few notes before the code! This list is designed for integers, but I plan to “extend” it somehow and it can be improved a lot. In my future posts I’ll post something more about the complexity of the algorithm and an analysis of it.

class Node
{
    public $data;
    public $next;
    public $prev;
 
    public function __construct($data, $prev, $next)
    {
        $this->data = $data;
        $this->prev = $prev;
        $this->next = $next;
    }
}
 
class LinkedList
{
    protected $front = null;
 
    public function add($data)
    {
        if (!$this->front) {
            $node = new Node($data, null, null);
            $this->front = &$node;
        } else {
            if ($data < $this->front->data) {
                $node = new Node($data, null, $this->front);
                $this->front = $node;
                return;
            }
 
            $current = $this->front;
            while ($current) {
                if ($current->data < $data && isset($current->next) && $current->next->data > $data) {
                    $node = new Node($data, $current, $current->next);
                    $current->next = $node;
                }
                if ($current->data < $data && !isset($current->next)) {
                    $node = new Node($data, $current, $current->next);
                    $current->next = $node;
                }
                $current = $current->next;
            }
        }
    }
 
    public function printl()
    {
        $current = &$this->front;
        while($current) {
            echo $current->data, '<br />';
            $current = $current->next;
        }
    }
}
 
$list = new LinkedList();
$list->add(13);
$list->add(14);
$list->add(15);
$list->add(11);
$list->add(12);
$list->add(17);
$list->add(10);
$list->add(16);
 
$list->printl();