Develop Reference

Issue with image load recursive chain on slow network/mobile

So basically I have a page with a few sections. Each sections contains 5-30 image icons that are fairly small in size but large enough that I want to manipulate the load order of them.
I'm using a library called collagePlus which allows me to give it a list of elements which it will collage into a nice image grid. The idea here is to start at the first section of images, load the images, display the grid, then move on to the next section of images all the way to the end. Once we reach the end I pass a callback which initializes a gallery library I am using called fancybox which simply makes all the images interactive when clicked(but does not modify the icons state/styles).
var fancyCollage = new function() { /* A mixed usage of fancybox.js and collagePlus.js */
var collageOpts = {
'targetHeight': 200,
'fadeSpeed': 2000,
'allowPartialLastRow': true
};
// This is just for the case that the browser window is resized
var resizeTimer = null;
$(window).bind('resize', function() {
resetCollage(); // resize all collages
});
// Here we apply the actual CollagePlus plugin
var collage = function(elems) {
if (!elems)
elems = $('.Collage');
elems.removeWhitespace().collagePlus(collageOpts);
};
var resetCollage = function(elems) {
// hide all the images until we resize them
$('.Collage .Image_Wrapper').css("opacity", 0);
// set a timer to re-apply the plugin
if (resizeTimer) clearTimeout(resizeTimer);
resizeTimer = setTimeout(function() {
collage(elems);
}, 200);
};
var setFancyBox = function() {
$(".covers").fancybox({/*options*/});
};
this.init = function(opts) {
if (opts != null) {
if (opts.height) {
collageOpts.targetHeight = opts.height;
}
}
$(document).ready(function() {
// some recursive functional funk
// basically goes through each section then each image in each section and loads the image and recurses onto the next image or section
function loadImage(images, imgIndex, sections, sectIndex, callback) {
if (sectIndex == sections.length) {
return callback();
}
if (imgIndex == images.length) {
var c = sections.eq(sectIndex);
collage(c);
images = sections.eq(sectIndex + 1).find("img.preload");
return loadImage(images, 0, sections, sectIndex + 1, callback);
}
var src = images.eq(imgIndex).data("src");
var img = new Image();
img.onload = img.onerror = function() {
images[imgIndex].src = src; // once the image is loaded set the UI element's source
loadImage(images, imgIndex + 1, sections, sectIndex, callback)
};
img.src = src; // load the image in the background
}
var firstImgList = $(".Collage").eq(0).find("img.preload");
loadImage(firstImgList, 0, $(".Collage"), 0, setFancyBox);
});
}
}
From my galleries I then call the init function.
It seems like my recursive chain being triggered by img.onload or img.onerror is not working properly if the images take a while to load(on slow networks or mobile). I'm not sure what I'm missing here so if anyone can chip in that would be great!
If it isn't clear what is going wrong from the code I posted you can see a live example here: https://www.yuvalboss.com/albums/olympic-traverse-august-2017
It works quite well on my desktop, but on my Nexus 5x it does not work and seems like the finally few collage calls are not happening. I've spent too long on this now so opening this up to see if I can get some help. Thanks everyone!

Whooooo I figured it out!
Was getting this issue which I'm still unsure about what it means
[Violation] Forced reflow while executing JavaScript took 43ms
Moved this into the callback that happens only once all images are loaded
$(window).bind('resize', function() {
resetCollage(); // resize all collages
});
For some reason it was getting called early even if the browser never resized causing collage to get called when no elements existed yet.
If anyone has any informative input as to why I was getting this js violation would be great to know so I can make a better fix but for now this works :):):)

ajax undefined after a thousand iterations

When creating an animation I try to use javascript for additional effects, namely snow being piled up and falling off the edges of the foreground. I figured that the javascript could do the "calculations" on a <canvas> that had the image, then send the "snow" to a php script that would create the png images. This is all placed on my local "server" because that is the only one that can write files.
<html>
<head>
<title>Making Snow</title>
</head>
<body bgcolor="black">
<canvas id="canvas" width="1920px" height="1080px"></canvas>
</body>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<script>
var canvas;
var ctx;
var frame=-530;
var simg = new Image()
var dimg = new Image()
onload = function()
{
canvas = document.getElementById("canvas");
ctx = canvas.getContext("2d");
simg.src = "prodB/C/DGB.0530.png"
}
simg.onload = function()
{
var ipo=3;
// Initialize all pixels on the screen/page
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.drawImage(simg,0,0);
document.title = "Making Snow " + (frame+530) + " / 7000";
snowdraw();
}
dimg.onerror = function()
{
dimg.src = "../imagewriting/snow" + zeroFill(frame+530,4) + ".png";
}
dimg.onload = function()
{
frame++;
if(frame<530)
simg.src = "prodB/C/DGB.0530.png"
else if(frame>4400)
simg.src = "prodB/C/DGB.4400.png"
else
simg.src = "prodB/C/DGB." + zeroFill(frame,4) + ".png"
}
var snowdraw = function()
{
var temp;
var canvasData = "";
// console.log(screen);
// Animation
// Choose a random pixel at the top of the screen
if(frame<7000)
{
for(ny=canvas.height-2; ny>=0; ny--)
{ // Iterate through all the pixels starting from the bottom right corner.
for(nx=canvas.width-2; nx>=0; nx--)
{
canvasData=canvasData+"1";
}
}
$.ajax({
method: "POST",
url: "makesnow.php",
data:{ imgData: canvasData, frame: (frame+530) }
})
.done(function( msg ) {
dimg.src = "../imagewriting/snow" + zeroFill(frame+530,4) + ".png";
});
}
else
{
document.title = "COMPLETE";
}
}
// http://stackoverflow.com/questions/1267283/how-can-i-create-a-zerofilled-value-using-javascript
// by Peter Bailey http://stackoverflow.com/users/8815
function zeroFill( number, width )
{
width -= number.toString().length;
if ( width > 0 )
{
return new Array( width + (/\./.test( number ) ? 2 : 1) ).join( '0' ) + number;
}
return number + ""; // always return a string
}
</script>
</html>
However, on the 1640th frame (or more precisely frame=1110) ajax is suddenly undefined. The image snow1640.png is created, but the browser tells me ajax is not defined and won't advance passed Making Snow 1640 / 7000. Because of the small random nature for each "snow flake" I can't just pick it up from where I left off, as the snow would jump from one frame to the next. Though I did try that at one point and ajax still stopped after that frame.
I first ran it on the local machine running Firefox (http://127.0.0.1/...) then moved onto another machine on the network which is more powerful running Chrome and both died on that same frame. Thought it might be a memory or file limit so I moved the complete frames out of there. Still nothing.
EDIT: Code now snippit of just the problem.
Also, console.log for data and ajax.responseText seem to be generally empty, both during successful "renders" and when it starts iterating ajax is not defined (every other line empty, every other error).
EDIT: New development! Turns out that the error ReferenceError: ajax is not defined anyways gets called between frames (and the 404 when asking dimg if image was created).
EDIT: By typing in console.log($.ajax) after onload and commenting out simg.src I got function ajax().
Error persists, this time I expanded it to reveal the following:
success http://127.0.0.1/ag/makesnowBC.html 197:7
j http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js 2:27131
fireWith http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js 2:27949
x http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js 4:22242
b http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js 4:26298
EDIT: Changed the code to now use Synchronous ajax. This time there are no error messages what so ever, but it still stops at 1640.

Media Source Extensions Not Working

I am trying to use the MediaSource API to append separate WebM videos to a single source.
I found a Github project that was attempting the same thing, where a playlist of WebMs is loaded, and each one is appended as a SourceBuffer. But it was last committed a year ago, and thus out-of-sync with the current spec. So I forked it and updated to the latest API properties/methods, plus some restructuring. Much of the existing code was taken directly from the spec’s examples and Eric Bidelman’s test page.
However, I can not get it to work as expected. I am testing in two browsers, both on Mac OS X 10.9.2: Chrome 35 stable (latest at the time of this writing), and Firefox 30 beta with the flag media.mediasource.enabled set to true in about:config (this feature will not be introduced until FF 25, and current stable is 24).
Here are the problems I’m running into.
Both browsers
I want the video to be, in the end, one long video composed of the 11 WebMs (00.webm, 01.webm, …, 10.webm). Right now, each browser only plays 1 segment of the video.
Chrome
Wildly inconsistent behavior. Seems impossible to reproduce any of these bugs reliably.
Sometimes the video is blank, or has a tall black bar in the middle of it, and is unplayable.
Sometimes the video will load and pause on the first frame of 01.webm.
Sometimes, the video will play a couple of frames of the 02.webm and pause, having only loaded the first three segments.
The Play button is initially grayed out.
Pressing the grayed out Play button produces wildly inconsistent behaviors. Sometimes, it loads a black, unplayable video. Other times, it will play the first segment, then, when you get to the end, it stops, and when you press Play/Pause again, it will load the next segment. Even then, it will sometimes skip over segments and gets stuck on 04.webm. Regardless, it never plays the final segment, even though the console will report going through all of the buffers.
It is honestly different every time. I can’t list them all here.
Known caveats: Chrome does not currently implement sourceBuffer.mode, though I do not know what effect this might have.
Firefox
Only plays 00.webm. Total running time is 0:08, the length of that video.
Video seeking does not work. (This may be expected behavior, as there is nothing actually happening in the onSeeking event handler.)
Video can not be restarted once finished.
My initial theory was that this had to do with mediaSource.sourceBuffers[0].timestampOffset = duration and duration = mediaSource.duration. But I can’t seem to get anything back from mediaSource.duration except for NaN, even though I’m appending new segments.
Completely lost here. Guidance very much appreciated.
EDIT: I uncommented the duration parts of the code, and ran mse_webm_remuxer from Aaron Colwell's Media Source Extension Tools (thanks Adam Hart for the tips) on all of the videos. Voila, no more unpredictable glitches in Chrome! But alas, it still pauses once a media segment ends, and even when you press play, it sometimes gets stuck on one frame.
In Firefox Beta, it doesn’t play past the first segment, responding with:
TypeError: Value being assigned to SourceBuffer.timestampOffset is not a finite floating-point value.
Logging the value of duration returns NaN (but only in FF).

The main problem is with the video files. If you open chrome://media-internals/ you can see error Media segment did not begin with keyframe. Using properly formatted videos, like the one from Eric Bidelman's example (I hope he doesn't get mad that I keep linking directly to that video, but it's the only example video I've found that works), your code does work with the following change in appendNextMediaSegment():
duration = mediaSource.duration;
mediaSource.sourceBuffers[0].timestampOffset = duration;
mediaSource.sourceBuffers[0].appendBuffer(mediaSegment);
You can try Aaron Colwell's Media Source Extension Tools to try to get your videos working, but I've had limited success.
It also seems a little weird that you're looking at the onProgress event before appending segments, but I guess that could work if you only want to append if the video is actually playing. It could make the seekbar act odd since the video length is unknown, but that can be a problem in any case.

I agree with the opinion Adam Hart said. With a webm file, I tried to implement an example like http://html5-demos.appspot.com/static/media-source.html and then made a conclusion that its problem caused the source file I used.
If you have an arrow left, how about trying to use "samplemuxer" introduced at https://developer.mozilla.org/en-US/docs/Web/HTML/DASH_Adaptive_Streaming_for_HTML_5_Video.
In my opinion, samplemuxer is one of encoders like FFMPEG.
I found that the converted file works with mediaSource API. If you will also see it works, please let me know.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>MediaSource API Demo</title>
</head>
<body>
<h3>Appending .webm video chunks using the Media Source API</h3>
<section>
<video controls autoplay width="320" height="240"></video>
<pre id="log"></pre>
</section>
<script>
//ORIGINAL CODE http://html5-demos.appspot.com/static/media-source.html
var FILE = 'IU_output2.webm';
var NUM_CHUNKS = 5;
var video = document.querySelector('video');
var mediaSource = new MediaSource();
video.src = window.URL.createObjectURL(mediaSource);
function callback(e) {
var sourceBuffer = mediaSource.addSourceBuffer('video/webm; codecs="vorbis,vp8"');
logger.log('mediaSource readyState: ' + this.readyState);
GET(FILE, function(uInt8Array) {
var file = new Blob([uInt8Array], {type: 'video/webm'});
var chunkSize = Math.ceil(file.size / NUM_CHUNKS);
logger.log('num chunks:' + NUM_CHUNKS);
logger.log('chunkSize:' + chunkSize + ', totalSize:' + file.size);
// Slice the video into NUM_CHUNKS and append each to the media element.
var i = 0;
(function readChunk_(i) {
var reader = new FileReader();
// Reads aren't guaranteed to finish in the same order they're started in,
// so we need to read + append the next chunk after the previous reader
// is done (onload is fired).
reader.onload = function(e) {
try {
sourceBuffer.appendBuffer(new Uint8Array(e.target.result));
logger.log('appending chunk:' + i);
}catch(e){
console.log(e);
}
if (i == NUM_CHUNKS - 1) {
if(!sourceBuffer.updating)
mediaSource.endOfStream();
} else {
if (video.paused) {
video.play(); // Start playing after 1st chunk is appended.
}
sourceBuffer.addEventListener('updateend', function(e){
if( i < NUM_CHUNKS - 1 )
readChunk_(++i);
});
} //end if
};
var startByte = chunkSize * i;
var chunk = file.slice(startByte, startByte + chunkSize);
reader.readAsArrayBuffer(chunk);
})(i); // Start the recursive call by self calling.
});
}
mediaSource.addEventListener('sourceopen', callback, false);
// mediaSource.addEventListener('webkitsourceopen', callback, false);
//
// mediaSource.addEventListener('webkitsourceended', function(e) {
// logger.log('mediaSource readyState: ' + this.readyState);
// }, false);
function GET(url, callback) {
var xhr = new XMLHttpRequest();
xhr.open('GET', url, true);
xhr.responseType = 'arraybuffer';
xhr.send();
xhr.onload = function(e) {
if (xhr.status != 200) {
alert("Unexpected status code " + xhr.status + " for " + url);
return false;
}
callback(new Uint8Array(xhr.response));
};
}
</script>
<script>
function Logger(id) {
this.el = document.getElementById('log');
}
Logger.prototype.log = function(msg) {
var fragment = document.createDocumentFragment();
fragment.appendChild(document.createTextNode(msg));
fragment.appendChild(document.createElement('br'));
this.el.appendChild(fragment);
};
Logger.prototype.clear = function() {
this.el.textContent = '';
};
var logger = new Logger('log');
</script>
</body>
</html>
another test code
<!DOCTYPE html>
<html>
<head>
<title>MediaSource API Demo</title>
</head>
<body>
<h3>Appending .webm video chunks using the Media Source API</h3>
<section>
<video controls autoplay width="320" height="240"></video>
<pre id="log"></pre>
</section>
<script>
//ORIGINAL CODE http://html5-demos.appspot.com/static/media-source.html
var FILE = 'IU_output2.webm';
// var FILE = 'test_movie_output.webm';
var NUM_CHUNKS = 10;
var video = document.querySelector('video');
var mediaSource = new MediaSource();
video.src = window.URL.createObjectURL(mediaSource);
function callback(e) {
var sourceBuffer = mediaSource.addSourceBuffer('video/webm; codecs="vorbis,vp8"');
logger.log('mediaSource readyState: ' + this.readyState);
GET(FILE, function(uInt8Array) {
logger.log('byteLength:' + uInt8Array.byteLength );
sourceBuffer.appendBuffer(uInt8Array);
});
}
mediaSource.addEventListener('sourceopen', callback, false);
// mediaSource.addEventListener('webkitsourceopen', callback, false);
//
// mediaSource.addEventListener('webkitsourceended', function(e) {
// logger.log('mediaSource readyState: ' + this.readyState);
// }, false);
function GET(url, callback) {
var xhr = new XMLHttpRequest();
xhr.open('GET', url, true);
xhr.responseType = 'arraybuffer';
xhr.send();
xhr.onload = function(e) {
if (xhr.status != 200) {
alert("Unexpected status code " + xhr.status + " for " + url);
return false;
}
callback(new Uint8Array(xhr.response));
};
}
</script>
<script>
function Logger(id) {
this.el = document.getElementById('log');
}
Logger.prototype.log = function(msg) {
var fragment = document.createDocumentFragment();
fragment.appendChild(document.createTextNode(msg));
fragment.appendChild(document.createElement('br'));
this.el.appendChild(fragment);
};
Logger.prototype.clear = function() {
this.el.textContent = '';
};
var logger = new Logger('log');
</script>
</body>
</html>
Thanks.

Broken Youtube thumbnails do not fire error callback

Will an image error callback fire if an image is 404, but the host returns an image anyway?
I am trying to determine on the client whether a Youtube thumbnail is valid before submitting the URL to the server. Normally you can generate a thumbnail URL without querying their API with the format http://img.youtube.com/vi/**ID**/maxresdefault.jpg
Some videos do not have high-res thumbnails, for example, this one:
http://img.youtube.com/vi/ty62YzGryU4/maxresdefault.jpg
However, a lower quality thumbnail always exists:
http://img.youtube.com/vi/ty62YzGryU4/default.jpg
Ideally I would be able to detect whether the thumbnail did load via this code snippet, which would call "done" when it loaded a valid thumbnail:
var id = "ty62YzGryU4"
var tries = 0
var thumb = "http://img.youtube.com/vi/" + id + "/maxresdefault.jpg"
var img = new Image ()
img.onload = function(){ console.log('ok'); done(id, thumb) }
img.onerror = function(){
switch (tries++){
case 0:
img.src = thumb = "http://img.youtube.com/vi/" + id + "/hqdefault.jpg"
break;
case 1:
img.src = thumb = "http://img.youtube.com/vi/" + id + "/default.jpg"
break;
case 2:
done(id, thumb)
break;
}
}
img.src = thumb
if (img.complete) img.onload()
However this is not the case -- while I see a 404 error in the console, neither the onload nor the onerror callbacks fire, and thus done is never called.
If I set img.crossOrigin = "Anonymous" the onerror callback fires... for every thumbnail, because of the accursed Cross-Origin Resource Sharing policy.
I have also tried crafting an XMLHttpRequest, but to no avail:
xmlhttp = new XMLHttpRequest()
xmlhttp.onreadystatechange = function() {
console.log(xmlhttp.readyState)
console.log(xmlhttp.status)
};
xmlhttp.open('GET', url, true);
xmlhttp.send(null);
Whether I set X-Requested-With: XMLHttpRequest or not, the readyState goes from 1 to 4 but status is always zero!
Is there any way to see if this particular image gave a 404 without using the API?

YouTube thumbnails will not fire the onerror() function because YouTube sends another base64 gif image which shows the empty video icon which has the resolution of 120X90. (this is the key to the solution)
Note that you should load the image tag with the maxresdefault image and give it or (them) a certain class, e.g. "youtube-thumb".
For info: maxresdefault 1080, sddefault 720, hqdefault 480, mqdefault 360, default 240.
According to limited experiments, 0.jpg is 480 or the best low-res image available for a video.
$(function()
{
$('.youtube-thumb').each(function(ix, it){
if($(it)[0].naturalHeight <= 90 )
{
var path = $(it).attr('src');
var altpath = path.replace('maxresdefault.jpg','0.jpg');
$(it).attr('src', altpath);
}
});
});

I know this question is a bit older but I had the same problem today and I want to give you my solution which tries all of the YouTube thumbnails from best to worst.
My "ranking" of the different options is:
maxresdefault
mqdefault -> only one besides 1) that doesn't have black borders
sddefault
hqdefault
default -> works 100%
This is my code.
function youtube_check(e) {
var thumbnail = ["maxresdefault", "mqdefault", "sddefault", "hqdefault", "default"];
var url = e.attr("src");
if (e[0].naturalWidth === 120 && e[0].naturalHeight === 90) {
for (var i = 0, len = thumbnail.length - 1; i < len; i++) {
if (url.indexOf(thumbnail[i]) > 0) {
e.attr("src", url.replace(thumbnail[i], thumbnail[i + 1]));
break;
}
}
}
}
<img onload="youtube_check($(this))" src="https://i3.ytimg.com/vi/---ID---/maxresdefault.jpg">

jquery image load() and set timeout conflict in IE

As I hover a small img, I read it's larger image attribute, and create that image to display.
The problem is that I want to set Timeout before to display the image.
And while waiting for that timeout, we suppose to already have set an src to make it load early.
For some reason it never works in IE. ie, it only triggers the load even on the second time I hover the small image. I've no idea what has gone wrong with it, I had very similar animation on the other page it has been working just fine with a timeout.
Any ideas?..
$(document).ready(function(){
var nn_pp_trail=0;
$('div.nn_pp_in').hover(function(){
var limg=$(this).children('img').attr('limg');
var img=new Image();
//img.src=limg;
img.className='nn_pp_z';
img.src=limg;
var a=(function(img,par,limg){
return function(){
nn_pp_trail=window.setTimeout(showtrail,50);
$(img).one('load',(function(par){ //.attr('src',limg).
return function(){
// alert('loaded');
window.clearTimeout(nn_pp_trail);
hidetrail();
var width=this.width;
var height=this.height;
var coef=width/313;
var newHeight=height/coef;
var newHpeak=newHeight*1.7;
var nn=par.parents('.tata_psychopata').nextAll('.nn_wrap').first();
var pheight=nn.height();
var ptop=nn.position().top-2+pheight/2-1;
var pleft=nn.position().left+90+157-1;
$(this).appendTo(nn).css('left',pleft+'px').css('top',ptop+'px')
.animate({opacity:0.6},0)
.animate({opacity:1,top:'-='+newHpeak/2+'px',height:'+='+(newHpeak)+'px',left:'-=10px',width:'+=20px'},130,(function(newHeight,newHpeak){
return function(){
$(this).animate({left:'-='+(156-10)+'px',width:'+='+(313-20)+'px',height:newHeight+'px',top:'+='+(newHpeak-newHeight)/2+'px'},200,function(){});
}
})(newHeight,newHpeak)
);
}
})(par)
).each(function(){
if(this.complete || this.readyState == 4 || this.readyState == "complete" || (jQuery.browser.msie && parseInt(jQuery.browser.version) <=6))
$(this).trigger("load");}); ;
}
})(img,$(this),limg);
window.setTimeout(a,20); //if I set 0 - it loads all the time.
//if I set more than 0 timeout
//the load triggers only on the 2nd time I hover.
$(this).data('img',$(img));
},function(){
});
});

img.src=limg;
This was the problem, in IE we need not to set src as we create an image object, but first attach load event to it, and only then set attr src, and then trigger complete with an each, eg:
img.one(load, function(){}).attr('src','i.png').each(function(){ /*loaded? then it's complete*/ });
Hope someone learn on my mistakes :-)

Thank you, this helped me a lot. I had a similar situation.
As you said: First the "load"-event, then the "src" for IE.
// This was not working in IE (all other Browsers yes)
var image = new Image();
image.src = "/img/mypic.jpg";
$(image).load(function() {
//pic is loaded: now display it
});
// This was working well also in IE
var image = new Image();
imagSrc = "/img/mypic.jpg";
$(image).load(function() {
//pic is loaded: now resize and display
}).attr('src',imageSrc);