Sorted data can dramatically change the speed of our program, therefore sorting algorithms are something quite special in computer science. For instance searching in a sorted list is faster than searching in an unordered list.

There are two main approaches in sorting – by comparing the elements and without comparing them. A typical algorithm from the first group is insertion sort. This algorithm is very simple and very intuitive to implement, but unfortunately it is not so effective compared to other sorting algorithms as quicksort and merge sort. Indeed insertion sort is useful for small sets of data with no more than about 20 items.

Insertion sort it is very intuitive method of sorting items and we often use it when we play card games. In this case the player often gets an unordered set of playing cards and intuitively starts to sort it. First by taking a card, making some comparisons and then putting the card on the right position.

So let’s say we have an array of data. In the first step the array is unordered, but we can say that it consists of two sub-sets: sorted and unordered, where on the first step the only item in the sorted sub-set is its first item. If the length of the array is n the algorithm is considered completed in n-1 steps. On each step our sorted subset is growing with one item. The thing is that we take the first item from the unordered sub-set and with some comparisons we put it into its place in the sorted sub-set, like on the diagram bellow.

Implementation

Here’s a quick implementation of insertion sort in PHP. The good thing is that it is easy to implement, but there are bad news too – insertion sort is slow and it is ineffective for large data sets.

$data = array(4, 2, 4, 1, 2, 6, 8, 19, 3);

function insertion_sort(&$arr)
{
	$len = count($arr);
	
	for ($i = 1; $i < $len; $i++) {
		$tmp = $arr[$i];
		$j = $i;
		
		while (($j >= 0) && ($arr[$j-1] > $tmp)) {
			$arr[$j] = $arr[$j-1];
			$j--;
		}
		$arr[$j] = $tmp;
	}
}

We can improve this code a little by using a sentinel, just like the sequential search, in order to remove one of the comparisons.

$data = array(4, 2, 4, 1, 2, 6, 8, 19, 3);

function insertion_sort_sentinel(&$arr)
{
	$len = count($arr);
	array_unshift(&$arr, -1);
	
	for ($i = 1; $i < $len+1; $i++) {
		$tmp = $arr[$i];
		$j = $i;
		
		while ($arr[$j-1] > $tmp) {
			$arr[$j] = $arr[$j-1];
			$j--;
		}
		$arr[$j] = $tmp;
	}
	array_shift(&$arr); // remove the sentinel
}

Just because we use searching the right position in an ordered array we can use binary search in order to improve even more the algorithm above. Unfortunately this doesn’t improve so much the general efficiency of this algorithm.

Complexity

As I said this algorithm is not so effective. Its complexity is O(n²) which is far worse than the O(n*log(n)) of quicksort, as you can see on the diagram bellow.

Application

This algorithm is useful for small sets of data and even if it doesn’t look like the most effective sorting algorithm, insertion sort can be useful for some reasons. First of all it is easy to implement, but it also does not require additional memory and it can be fast if the data is almost nearly sorted, which is great.

It’s really full of video sharing websites out there, but in fact almost all of them use Flash player to display their video files. This is the reality now, but with the coming of HTML5, perhaps the things are changing a bit!

First of all if you start dealing with video sharing platforms the first thing to do maybe is to find a good Flash (.flv) player and to convert all your video content in FLV.

Few things to know with Flash video players:

1. The user can play those videos only after installing the Flash Plugin to his browser;
2. The video must be encoded either in FLV (or FLash Video) or in MPEG-4 with h.264 codec. Only than the Flash player can play it;

The HTML5, which can be described as variety of new “things” in the HTML comes with a native <video> tag. Something like the <img> tag where you can just point the source of the image in the src attribute.

First Question – How Does it Look Like?

To get more fluent with the <video> tag you must simply thing of it as a “complex” <img> tag. You just point to the video and the browser will do the rest. To be more exact let me send you to the w3schools page, but the important thing as they say:

Until now, there has never been a standard for showing video on a web page.

However to start from somewhere here’s a little snippet showing you the basic, but very basic usage of the HTML5 video tag:

<video src="path_to_the_video" controls="controls"></video>

Second Question – Is Every Video Playable?

But of course not! There are different browser – different video formats. Currently there are three formats, supported by the different browsers.

1. H.264
2. VP8
3. Theora

Note that these are video codecs and a video files does not consists of only a video codec, but also of an audio codec. This makes the video file a container of several things. As you may know already H.264 is used with MPEG-4 video format, which results in .mp4 extended files, Theora is used in OGG, which are all those .ogg files out in the web, and finaly VP8 is used in WebM … or in .webm videos.

First thing to know FLV files (.flv) can also be encoded with H.264. Actually Flash player has a h.264 decoder so this makes it possible to play both .mp4 and .flv files encoded with H.264.

Second thing to notice – where are those .webm files? I’ve never seen them!

Third Question – What is WebM and VP8?

Behind WebM and VP8 is Google. This is a new video format based again on Theora. Actually it pretends to be as good in compressing as H.264, which by the way is meant to be the best. But let me take a look at Nettuts+:

VP8, a relatively new codec, is the brainchild of On2 — the same guys behind Theora. Google acquired On2 in 2010, and opened up all the underlying patents for the codec into the public domain.

WebM, the container of choice for most current browsers, utilizes VP8 for compressing its video content and Vorbis for its audio. It produces content similar in quality to H.264.

It is completely royalty free, now and for the future. On the downside, though, it has limited hardware decoding support as well as third party device/mobile support.

Final Question – How Can I Convert a Video in WebM?

This answer is given by this article, where as it is said after having the ffmpeg version >= 0.6 you simply can use this command:

ffmpeg -i girltalk.mp4 -f webm -vcodec libvpx -acodec libvorbis -aq 90 -ac 2 girltalk.webm

Conclusion

It’s interesting to see what will happen one day. There is going to be either a harmonious life in the web video field or the codecs/formats will be as much as the browser? Who knows?

The task is to read the entire Gdata from a YouTube’s channel. It may sound easy, but as you may know Gdata is based on the Atom publishing protocol, and it naturally gives you only the latest few items.

Of course Zend Framework has a large set of classes dealing with Google’s Gdata services, one of them is the Zend_Gdata_YouTube.

It gives you the power to iterate/paginate over the entire set of YouTube user’s/channel’s videos. In that example let’s assume you have a protected function doing the reading of a single portion:

protected function _process(Zend_Gdata_YouTube_VideoFeed $videoFeed)
{

    /* @var $entry Zend_Gdata_YouTube_VideoEntry */
    foreach ($videoFeed as $entry) {
        /* @var $published Zend_Gdata_App_Extension_Published */
        $published = $entry->getPublished();
        $thumbnails = $entry->getVideoThumbnails();

        // set date format
        $date = new Zend_Date($published->getText());

        // array
        $tags = $entry->getVideoTags();

        $data['title'] = $entry->getVideoTitle();
        $data['description'] = $entry->getVideoDescription();
        $data['date'] = $date->get('Y-MM-d hh:mm:ss');
        $data['thumb'] = @$thumbnails[3]['url'];
        $data['id'] = $entry->getVideoId();
        $data['flash_player'] = $entry->getFlashPlayerUrl();
        $data['tags'] = implode(',', $tags) . ', ' . $entry->getVideoCategory();
        // do whatever you want with the data
    }

}

The only thing left is to iterate over the “pages” of the feed. This can be done with getNextFeed() method.

public function readRssAction()
{
    $userId = 'some_user';
    $client = new Zend_Http_Client();
    $gdata = new Zend_Gdata_YouTube($client, 'my-app', null, $this->_apiKey);
    $videoFeed = $gdata->getUserUploads($userId);

    // save the last items
    $this->_process($videoFeed);

    try {
        while ($videoFeed = $videoFeed->getNextFeed()) {
            $this->_process($videoFeed);
        }
    } catch (Zend_Gdata_App_Exception $e) {
        echo $e->getMessage();
    }
}

You’ll get an exception when there is no more feeds to process!

To combine all this into a single controller and to complete the code here’s the entire source:

class YoutubeController extends Zend_Controller_Action
{
    protected $_apiKey = 'your_api_key_goes_here';

    protected function _process(Zend_Gdata_YouTube_VideoFeed $videoFeed)
    {

        /* @var $entry Zend_Gdata_YouTube_VideoEntry */
        foreach ($videoFeed as $entry) {
            /* @var $published Zend_Gdata_App_Extension_Published */
            $published = $entry->getPublished();
            $thumbnails = $entry->getVideoThumbnails();

            // set date format
            $date = new Zend_Date($published->getText());

            // array
            $tags = $entry->getVideoTags();

            $data['title'] = $entry->getVideoTitle();
            $data['description'] = $entry->getVideoDescription();
            $data['date'] = $date->get('Y-MM-d hh:mm:ss');
            $data['thumb'] = @$thumbnails[3]['url'];
            $data['id'] = $entry->getVideoId();
            $data['flash_player'] = $entry->getFlashPlayerUrl();
            $data['tags'] = implode(',', $tags) . ', ' . $entry->getVideoCategory();
            // do whatever you want with the data
        }
    }

    public function readRssAction()
    {
        $userId = 'some_user';
        $client = new Zend_Http_Client();
        $gdata = new Zend_Gdata_YouTube($client, 'my-app', null, $this->_apiKey);
        $videoFeed = $gdata->getUserUploads($userId);

        // save the last items
        $this->_process($videoFeed);

        try {
            while ($videoFeed = $videoFeed->getNextFeed()) {
                $this->_process($videoFeed);
            }
        } catch (Zend_Gdata_App_Exception $e) {
            echo $e->getMessage();
        }
    }
}

Note: here you’ve to substitute the API key with the one you’ve for your development.

And if these “big players” are going that way, don’t hesitate to follow them! HTML5 is really what we as web developers were waiting for so long and even all of the problems during its standardization process it’s really cool there will be tags like video.

What YouTube is doing today, perhaps will seem normal to everyone tomorrow. However there are some questions still with no answer, as where the flash possibility to add ads into the player is going?! But we’re about to see great things from these two sites!

Just check out these two links:

Youtube HTML5

Vimeo