Tag Archives: jquery

Yeah so my audio player in jQuery Mobile and NodeJS (part 2)

Ok so my prev post was about how to construct a playlist in jQuery Mobile with some simple NodeJS file serving. This one is to construct the audio player itself! Mine looks like this (cause I was kinda too lazy to do the styling properly):

My audio player

My audio player

Ok so it’s very basic: we got a toggle Play/Pause button, Next button, Prev button, the progress bar for download progress and a fake album art (cause I didn’t know how to extract mp3 metadata yet). The features that I implemented are pretty basic:

1. Play/Pause

2. Next/Prev Song

3. Progress bar for song buffering

4. Time Left

5. Auto-play the next one if this one ended

6. Header shows song name

The HTML structure itself is rather simple as jQuery Mobile does most of the styling for u:


<div data-role="page" class="player">

    <div data-role="header">
        <h1>My collection</h1>
    </div><!-- /header -->

    <div data-role="content">

	<div class='cover-art' style='text-align:center'>
		<audio src='music/kpop/ttl2.mp3' preload autoplay></audio>
		<img src='images/no-album-art.png' />
	</div>
    </div><!-- /content -->
    <div data-role='footer' style='text-align:center'>
	<p class='track-info'>
		<span class="song-progress">
			<input type="range" min="0" max="100" value="0" />
		</span>
		<span class="timeleft"></span>
	</p>
	<div class='playback' data-role="controlgroup" data-type='horizontal' style='text-align:center'>
<button class='playback-prev' data-icon='back'>Prev</button>
<button class='playback-play' >||</button>
<button class='playback-next' data-icon="forward" data-iconpos="right">Next</button>
</div>
	</div>
<script type="text/javascript">
	$('div.player').bind('pageshow', function(ev, ui) {
		if (!$(this).attr('data-init')) {
			Player.init('div.player.ui-page-active', $.getUrlVar($(this).attr('data-url'), 'song'));
			$(this).attr('data-init', 'true');
		}
	});
</script>
</div><!-- /page -->

So again, I bind some initialization to the “pageshow” event of the page and make sure it doesn’t get initialized twice. Since the href in each <li> points to the same page but different parameter, jQuery loads this again every single time even if it’s the same one. This only prevents the forward history button to reload the song. However, this does not prevent having multiple songs playing at the same time cause jQuery mobile loads those as different div. You can customize the changePage behavior when user clicks on a <li> but I didn’t, just to keep it simple.

The parameter is stored in the main player div (with selector “div.player”, class “ui-page-active” indicates its the active one) so $.getUrlVar just extract the parameter song from it (which indicates the song index):

$.extend({
	getUrlVars : function(string) {
		var vars = [];
		var hash;
		var href = string ? string : window.location.href;
		console.log(href);
		if (href.indexOf('#') > -1) {
			var hrefArr = href.split('#');
			href = hrefArr[hrefArr.length - 1];
		}
    		var hashes = href.slice(href.indexOf('?') + 1).split('&');
		for (var i = 0; i < hashes.length; i++) {
			hash = hashes[i].split('=');
			vars.push(hash[0]);
			vars[hash[0]] = hash[1];
		}
		return vars;
	},

	getUrlVar : function(string, name) {
		return $.getUrlVars(string)[name];
	}
});

Pretty simple, just basically splitting the data-url field into a map of parameter names and values. The Player.init function takes in the parent div selector (so that I can locate the control relative to the parent div) and the song index. I basically keep track of all the control DOM elements:

var $next = $(div + ' button.playback-next');
var $prev = $(div + ' button.playback-prev');
var $play = $(div + ' button.playback-play');
var $trackInfo = $(div + ' p.track-info');
var $songProgress = $trackInfo.find('.song-progress');
var $loading = $songProgress.find('.loading');
var $timeLeft = $trackInfo.find('.timeleft');
var $slider = $songProgress.find('.ui-slider');
var $handle = $slider.find('.ui-slider-handle');
$songProgress.find('input[type="number"]').hide();
var $title = $(div + ' h1.ui-title');
var $audio = $(div + ' audio');
var audio = $audio.get(0);

I have this habit of prefixing jQuery objects with $ to distinguish from actual DOM element ($audio is the jQuery-wrapped object of audio). Play/pause is really easy:

$play.click(function(ev) {
    var $buttonText = $(this).parent().find('.ui-btn-text');
    if (audio.paused) {
        $audio.attr('data-state', 'play');
        audio.play();
        $buttonText.text("||");
    }
    else {
        $audio.attr('data-state', 'pause');
        audio.pause();
        $buttonText.text("Play");
    }
});

Prev/Next is also straightforward:

$next.click(function(ev) {
    var state = $audio.attr('data-state');
    var current = parseInt($audio.attr('data-current'));
    Player.getSongPath(current + 1, $audio, $title, function() {
        $audio.attr('data-current', current + 1);
        if (state == 'play') {
            audio.play();
        }
    });
});
$prev.click(function(ev) {
    var state = $audio.attr('data-state');
    var current = parseInt($audio.attr('data-current'));
    Player.getSongPath(current - 1, $audio, $title, function() {
        $audio.attr('data-current', current - 1);
        if (state == 'play') {
            audio.play();
        }
    });
});

So we’ve done 1 and 2. Let’s jump to 5 cause its also easy:

$audio.bind('ended', function(ev) {
    $next.click();
});

I did 6 as a separate functionality that ping the server for the song’ path, change the audio source and also title:

getSongPath: function(index, $audio, $title, fn) {
    $.post('playlist?song=' + index, null, function(data) {
        console.log(data);
        $audio.attr('src', data.result);
        var filenameArr = data.result.split('/');
        var filename = filenameArr[filenameArr.length - 1];
        $title.text(filename);
        if ($.isFunction(fn)) {
            fn();
        }
    }, 'json');
}

For some reason I put null in the POST request data instead of the actual data (song=2) cause I wasn’t getting that data on the server side (I tried req.body, req.query and everything… didn’t seem to show up, will look into it a bit more). OK now lets get back to 3:

if (!$loading.get(0)) { //this inject the white loading bar before the handler
    $handle.before('<div class="ui-slider loading" style="width: 3%; float: left; top: 0; left: -3%; background-color: buttonface;"></div>');
    $loading = $slider.find('div.loading'); //update var
}
$audio.bind('progress', function() {
    var loaded = parseInt(((audio.buffered.end(0) / audio.duration) * 100) + 3, 10);
    $loading.css({
        width: loaded + '%' //change width accordingly
    });
});
var manualSeek = false;
var loaded = false;
$handle.css({
    top: '-50%' //somehow I think the styling of footer and handler conflicted and messed it up so I had to bump it up 50%
});

I actually didn’t know how to get the current time of the audio but after googling around and looking at audio attributes, things got a bit clearer. Here’s 4:

$audio.bind('timeupdate', function() {
    var rem = parseInt(audio.duration - audio.currentTime, 10),
        pos = Math.floor((audio.currentTime / audio.duration) * 100),
        mins = Math.floor(rem / 60, 10),
        secs = rem - mins * 60;
    $timeLeft.text('-' + mins + ':' + (secs > 9 ? secs : '0' + secs));
    if (!manualSeek) {
        $handle.css({
            left: pos + '%'
        });
    }
    if (!loaded) {
        loaded = true;
    }
});

Ok so that’s how I made a sorta functional audio player. There’re still problems with it but hopefully this DIY guide gave u some idea on how to control the audio element manually.

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What I’ve been up to… (a.k.a making an audio player using jQuery Mobile & NodeJS) Part 1

So I recently signed up for a VPS from AlienVPS at a ridiculously low price and guess what, it crashed on me twice today… -_- But $19/month is still pretty darn cheap. At least it gave me some sandbox to play around with NodeJS and jQuery Mobile.

OK so far NodeJS has been rather simple and straightforward. I actually use Express framework on top of NodeJS which ease the work a little bit. However, I can really see how this can become complicated really really fast. 1st of all, I sorta have to implement all the HTTP protocol code manually in NodeJS (except for 500 Internal Error and 200 OK I think). So that includes 404, 403, blah blah. Not that it matters that much except I wanna maximize my site traffic by taking advantage of Search Engine bots. Well I disallow everything in robots.txt right now so if those bots behave, I should be good. You can check it out at http://208.93.155.39:8080/playlist.html but please please don’t spread it around or I’m gonna have to shut it down due to my limited bandwidth. The app is still buggy since it’s a work in progress but a refresh should make it behave a bit better.

Anyway, now the 1st thing a web server should be able to do is to serve static web pages and it can be achieved pretty easily:

var app = require('express').createServer();
var fs = require('fs');
var public_path = 'public/';
var PORT = 8080;
app.get('/', function(req, res) {
        res.sendfile(public_path + 'index.html');
});
app.get('/*', function(req, res) {
        var page = req.params[0];
        res.sendfile(public_path + page);
});

Easy enuf… Now I want to query some specific stuff like, idk my KOREAN POP playlist!!

var songs;
app.post('/playlist.html', function(req, res){
        Controller.handlePlaylist(req, res);
});
var Playlist = {
        get : function(name) {
                return fs.readdirSync(public_path + MUSIC_PATH + name);
        }
};
var Controller = {
        handlePlaylist : function(req, res) {
                if (!songs) { //lazy-initialize this
                        songs = Playlist.get(req.param('playlist'));
                }
                var index = req.param('song');
                if (index && index >=0 && index < songs.length) { //if I query a specific song number, give me the path to the song
                        res.send({ 'result' : MUSIC_PATH + 'kpop/' + songs[index] });
                } else { //otherwise give me the whole list
                        res.send({ 'filenames' : songs });
                }
        }
};

Now when I hit up playlist.html?playlist=kpop with POST, I can get my playlist and playlist.html?song=1 with POST gives me the 2nd song. This is a simple enuf song serving mechanism that will help me build my audio player.

Playlist Page

Playlist Page

Since I’m not using any view rendering engine, in playlist.html I actually have to use the trick of loading the file 1st, then make an ajax call to populate the data. This gets very very tricky with jQuery mobile since it doesn’t have a lot of control events on when it’s done rendering and what not. This combines with ambiguous timing from AJAX callbacks can lead to a pretty disruptive UX (I’m still having trouble with synchronizing stuff in JavaScript). But anyway, the playlist.html has a pretty simple structure:

<div data-role="page" class="playlist">
    <div data-role="header">
        <h1>My collection</h1>
    </div><!-- /header -->

    <div data-role="content">
        <ul data-role="listview" data-inset="true">
                <li data-role="list-divider">Kpop</li>
        </ul>
    </div><!-- /content -->
    <script type='text/javascript'> 
    $('div.playlist').bind('pageshow', function() {
        var $page = $(this); // to use inside callback since "this" in the callback function is different
        if (!($page.attr('data-init'))) { // Initialize once
                $.post('playlist.html?playlist=kpop', null, function(data) { //retrieve the data
                        var i;
                        var filenames = data['filenames'];
                        var $playlist = $page.find('ul[data-role="listview"]');
                        for (i in filenames) { //populate the list of songs
                                $playlist.append('<li><a href="player.html?song=' + i + '">' + filenames[i] + '</a></li>'); 
                        }
                        $page.attr('data-init', 'true');
                        $playlist.listview('refresh'); //refresh the view
                }, 'json');
        }
    });
    </script>

</div><!-- /page -->

The HTML structure itself is simple the the JavaScript is kind of a hack. “Pageshow” event in jQuery Mobile gets invoked after page has been initialized (a.k.a after jQuery converts basic elements into its themed mobile looks). Why not “pagecreate” or “pagebeforecreate”? Because the callback is actually an AJAX call to grab the data and listview can only be refresh after it’s been initialized (also not guaranteed in the previous 2 event hooks). If I were to use a view rendering engine to populate the data, then send across the wire, I wouldn’t have had this problem so… something to look at next time.

OK so that’s the easy part, I write next time about how to actually make the player cause that took me like 3 days… >.< sleep now!

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Why I’m hooked on JavaScript!!

Now I’m apparently not even an expert at JavaScript but I’ve had some exposure to it in 1 way or another, mainly through using jQuery in my last project (which I totally dig!!). I’m still working on web development in general and that project in particular right now and my friend and I have been going back and forth between the popular languages/frameworks like Ruby on Rails, Django and NodeJS. Honestly, I’m kinda a fanboy for NodeJS… I really am. Here’s why:

Now JavaScript has been mainly used for client side in web browser. The interesting thing is that each big boss (Mozilla/Google/IE) seems to develop their own JS Compiler. The Google V8 Engine (which NodeJS is built on) seems to be the fastest one right now. I was pretty amazed when JS was used as a server side technology but if you break it down, I wouldn’t say it’s impossible.

IMHO, I guess the important thing about writing a server is to handle sockets and a few protocols (HTTP, TCP… stuff like that). Now protocols are (again, IMO) rules of how information should be positioned in a packet so you can do that with pretty much any language. Traditional server technologies like Apache Tomcat, Glassfish… have been spawning threads to handle each incoming request. That’s not necessarily a bad thing but the bottlenecks seem to come down to IO so there’s been drawbacks in terms of blocking threads when u do a long query and such. Now u can overcome that by implementing distributed systems with a load balancer on top, along with some request filtering and routing, at which point it becomes kinda costly.

NodeJS

NodeJS

NodeJS uses Event Queue which puts everything in there and does event loop and uses callback functions. So technically there’re no blocking and the app is very scalable, theoretically. With that said, a long query gets run and once it’s done the callback is invoked. Now that sounds kinda cool.

OK so it can handle HTTP request, what else? Another important thing I would say is the database, which kinda comes down to separate vendor. How does the server connects to the database? Using a driver! Java gets an advantage cause it maintains an interface for vendors to write drivers based on. RoR supports a couple of database technologies and so is Django. There’re enough database vendors and plugins out there that it’s gonna take a while for NodeJS to catch up on that front, I assume.

What else? Some process manipulations like File IO and such, cause apparently the server will need to, at some point, modify some file resources, invoke some processes and stuff like that. NodeJS does have this, although I’m not sure how stable/mature it is. But that should take care of it.

Now I’ve always thought that RoR and Django were booming due to their ability to do rapid prototyping/development really really fast. You can get started on a webapp at a reasonably good pace with those, thanks to ORM and dependency injection and all the fun stuff. Honestly, I’m kinda a purist to a degree that I don’t hate abstracting 1 language over another, but magic can be disastrous sometimes. I believe that I should hand-write SQL queries and HTML/CSS instead of using ORM and compiled HTML (such as erb/jsp/asp…) cause you get a better control over it. It gets hard to manage after a while but it’s easier to identify the bottleneck and optimize it, instead of optimizing RoR and hoping that would optimize SQL.

Besides, using compiled HTML puts more load on the server than client, which in a way provides a more stable outcome since client machines/browsers vary a lot. But again, back to mixed language kinda thing, gotta be careful.

1 of the things I found that is challenging to JavaScript is actually synchronization. Now according to my knowledge, browser JS is executed in a single thread so how come synchronization is a big deal? Because browsers render different things in a different threads (you’ve been wondering how they load part by part, right??). Now what that means is, browsers render images/HTML structure/CSS styling/JS separately in different threads so its was such a pain for me to get a consistent User Experience. I honestly haven’t dug around enough to solve this issue since the nature of callback is just like that. Putting timeout and synchronization variables don’t seem to suffice…

Wait, so what about setTimeout and setInterval and stuff, aren’t they supposed to give a better control? Well FYI, setTimeout to 1000ms doesn’t mean it’ll get executed after 1000ms. It means that’ll get executed after AT LEAST 1000ms (cause it’s a queue…) so yeah, still digging around.

Back to my project which is a CMS now might turn into an RDS, I honestly think all we need are those important features listed above. Worst case is that we write a thin layer of wrapper around the tools we want to use, then invoke shell processes for those. But anw, it comes down to a light, thin server framework cause we probably don’t need all the big guns (which can take tons of time to tune). So yeah, it’d be great to set foot on that!!!

 

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How to make a combobox with jQuery

So jQuery came out with a new version 1.4.2 recently and jQuery UI is trying catch up with its 1.8rc3 since 1.7.2 is not compatible with the new jQuery library itself. Since jQuery UI starts incorporating its own theme builder tool, I’ve been using it and it seems to be very nice and elegant itself.

jQueryUI has its own autocomplete feature and button so I just wanna combine them together to make a combobox, which acts as both a select box and an autocomplete field.

So the HTML is like this:

<input id="example-text-field" type="text" /><button></button>

Well you can dynamically adding the button and even the text field using jQuery manipulation method

We start with configuring the autocomplete text field first.

var $input = $('#example-text-field');
$input.autocomplete({
   source: 'ExampleAutocompleteServerHandler.do', //you obviously need the source, it can be a JavaScript array or string or some handler from the server
   minLength: 0, //important! You need to set minLength to 0 for the button to work
   delay: 0 //make it a bit faster since there's no delay
})
.css('float', 'left');

So the text field is done, now let’s move on to the button next to it:

var $btn = $input.siblings('button:first');
$btn.button({
   icons: {
      primary: "ui-icon-triangle-1-s" //this puts the down arrow into the button
   },
   text: false //no text inside the button, just the arrow
})
.removeClass("ui-corner-all")  //disable rounded corner, it's optional
.addClass("ui-button-icon")   //put in styling as a button icon since the default button is pretty big
.css({
   height: "17px",    //make it as high as the text field
   width: "18px",    //this is optional, you can make it as wide as you want
   float: 'left'    //float it to the left so that it's right next to the text field
})
.unbind('click')   //it's optional but I like to clear all events associated to it before binding new click event
.click(function() {   //set up click binding event
   if ($input.autocomplete("widget").is(":visible")) {   //close the displaying result if it's visible already
      $input.autocomplete("close");
      return false;
   }
   $input.autocomplete("search", ""); //pass empty string as search query, this is why you need to set minLength = 0 so that it still searches, but displays all possible choices
   $input.focus();  //focus on the text field
   return false;  //disable form submit
});

$input.parents(':first').find('.ui-autocomplete') //configure result display so that it won't shift down the content
.css('width', '150px')
.css('height', '100px')
.css('overflow', 'auto');

There you go, combobox is done, you can pack it into a plugin with jQuery or inside your main JavaScript file, up to you.

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