Develop Reference

Chrome HTML5 Video Buffering

I am using video.js to show video content. I have a program that handles the streaming requests so the source of the video tag is set to a program which serves up the requested bytes.
The issue is that Chrome is requesting the entire video, range header on the GET request:
Range:bytes=0-
What I need to happen is that Chrome requests the minimum amount of bytes in order to start playback. I understand that this could lead to a lag due to the high number of requests being made, but it's what I need :(
Does anyone know how I could limit the buffer Chrome uses for this element?
There is a similar question here: HTML5 audio/video stop buffer
I've tried setting preload to none. This works in that it prevents the initial buffering from taking place, before the user has click play. But once it starts, it requests the entire range :(((
Many thanks,
Arvy

Got it. The 206 Partial Content can be responded to with however many bytes you need to supply. The client (Chrome in my case) asks for more anyways as it didn't receive a full range the first time.
For example, here is the request header Range:bytes=1000048- This means that the client has requested the rest of the file starting at byte 1000048. The program does not need to respond with the full range, in my case I am returning only 500000 bytes, so I take the 1000048 and add 499999 to get the end byte and format the headers accordingly. Seems to work fine. Hope it helps someone.

HTML5 audio starts from the wrong position in Firefox

I'm trying to play an mp3 file and I want to jump to specific location in the file. In Chrome 33 on Windows, the file jumps the correct position (as compared with VLC playing the mp3 locally) but in Firefox 28 on Windows it plays too far forward and in Internet Explorer 11 it plays too far behind.
It used to work correctly in Firefox 27 and earlier.
Is there a better way of doing this?
EDIT: The problem doesn't even require SoundManager2. You can replicate the same issue with just the <audio> tag in Firefox. These two lines are all the code you need to reproduce it:
<audio autoplay id="audio" src="http://ivdemo.chaseits.co.uk/enron/20050204-4026(7550490)a.mp3" controls preload></audio>
<button onclick="javascript:document.getElementById('audio').currentTime = 10;">Jump to 10 secs "...be with us in, er, 1 minute... ok" </button>
Try it here: http://jsfiddle.net/cpickard/29Gt3/
EDIT: Tried with Firefox Nightly, no improvement. I have reported it as bug 994561 in bugzilla. Still looking for a workaround for now.

The problem lies in the VBR encoding of the mp3.
Download that mp3 to disk and convert it to fixed bit rate, say with Audacity.
Run the example from disk:
<audio autoplay id="audio" src="./converted.mp3" controls preload></audio>
<button onclick="javascript:document.getElementById('audio').currentTime = 10;">
Jump to 10 secs "...be with us in, er, 1 minute... ok" </button>
and it works fine for me.
So my suggestion for workaround is is to upload an alternative fixed-bit mp3 file in place of the one you are using. Then it should work in the current FFx.

I work on SoundJS and while implementing audio sprites recently ran into similar issues. According to the spec, setting the position of html audio playhead can be inaccurate by up to 300ms. So that could explain some of the issues you are seeing.
Interestingly, your fiddle plays correctly for me in FF 28 on win 8.1 if I just let it play through from the start.
There are also some known issues with audio length accuracy that may also have an effect, which you can read about here.
If you want precision, I would definitely recommend using Web Audio where possible or a library like SoundJS.
Hope that helps.

I met the same issue, and I solved it by converting my MP3 file to the CBR(Constant Bit Rate) format. Then, it can solve the inconsistent issue between the currentTime and the real sound.
Choose the CBR format
Steps:
Download and install "Audacity" (it's a free for any platform)
Open your MP3 file
Click [File] -> [Export] -> [Options] -> [Constant] (See: Converting MP3 to Constant Bit Rate)
Audacity will ask you to provide the LAME MP3 encoder
(See: [download and install the LAME MP3 encoder])
There will be no inconsistent/asynchronous issue.
Also see:
HTML5 audio starts from the wrong position in Firefox
Inconsistent seeking in HTML5 Audio player
tsungjung411#gmail.com

I just tried your code with another audio url here, it seemed to work and i did not experience a delay of any sort in Firefox( v29) which i did previously.
<audio autoplay id="audio" src="http://mediaelementjs.com/media/AirReview-Landmarks-02-ChasingCorporate.mp3" controls preload></audio>
I guess to jump around an audio file, your server must be configured properly.
The client sends byte range requests to seek and play certain regions of a file, so the server must response adequately:
In order to support seeking and playing back regions of the media that
aren't yet downloaded, Gecko uses HTTP 1.1 byte-range requests to
retrieve the media from the seek target position. In addition, if you
don't serve X-Content-Duration headers, Gecko uses byte-range requests
to seek to the end of the media (assuming you serve the Content-Length
header) in order to determine the duration of the media.
Hope this helps..
You could also try looking into Web Audio API for sound-effect-like playback which gives you some guarantees about the playback delays.

After testing the fiddle it is noticable that there is some issue with FF , anywho , after searching sometime , the issue is due to "Performance lag" , but the good news is that someone has found a solution to that issue , you may want to read this :
http://lowlag.alienbill.com/
a single script will solve it all.

Can I get the data of a cross-site <img/> tag as a blob?

I am trying to save a couple of images that are linked to by a webpage to offline storage. I'm using IndexedDB on Firefox and FileSystem API on Chrome. My code is actually an extension, so on Firefox I'm running on Greasemonkey, and on Chrome as a content script. I want this to be automated.
I am running into problem when I retrieve the image file. I'm using example code from the article titled Storing images and files in IndexedDB, but I get an error: the images I'm trying to download are on a different subdomain and the XHR fails.
XMLHttpRequest cannot load http://...uxgk.JPG. Origin http://subdomain.domain.com is not allowed by Access-Control-Allow-Origin.
On Firefox I could probably use GM_xmlhttpRequest and it'd work (the code works on both browsers when I'm in same-origin URLs), but I still need to solve the problem for Chrome, in which other constraints (namely, needing to interact with frames on the host page) require me to incorporate my script in the page and forfeit my privileges.
So it comes back to that I'm trying to figure out a way to save images that are linked to (and may appear in) the page to IndexedDB and/or FileSystem API. I either need to realize how to solve the cross-origin problem in Chrome (and if it requires privileges, then I need to fix the way I'm interacting with jQuery) or some kind of reverse createObjectURL. At the end of the day I need a blob (File object, as far as I understand) to put into the IndexedDB (Firefox) or to write to FileSystem API (Chrome)
Help, anyone?
Edit: my question may actually really come down to how I can use jQuery the way I want without losing my content script privileges on Chrome. If I do, I could use cross-origin XHRs on Chrome as well. Though I'd much rather get a solution that doesn't rely on that. Specifically since I'd like this solution if I get the script incorporated into the webpage, and not require it to be a content script/userscript.
Edit: I realized that the question is only about cross-site requests. Right now I have one of three ways to get the image blob, with the help of #chris-sobolewski, these questions and some other pages (like this), which can be seen in this fiddle. However, all of these require special privileges in order to run. Alas, since I'm running on a page with frames, because of a known defect in Chrome, I can't access the frames. So I can load a script into each frame by using all_frames: true, but I really want to avoid loading the script with every frame load. Otherwise, according to this article, I need to escape the sandbox, but then it comes back to privileges.

Since you are running on Chrome and Firefox, your answer is fortunately, yes (kind of).
function base64img(i){
var canvas = document.createElement('canvas');
canvas.width = i.width;
canvas.height = i.height;
var context = canvas.getContext("2d");
context.drawImage(i, 0, 0);
var blob = canvas.toDataURL("image/png");
return blob.replace(/^data:image\/(png|jpg);base64,/, "");
}
this will return the base64 encoded image.
from there you just call the function something along these lines:
image = document.getElementById('foo')
imgBlob = base64img(image);
Then go ahead and store imgBlob.
Edit: As file size is a concern, you can also store the data as a canvasPixelArray, which is width*height*4 bytes in size.
imageArray = context.getImageData( 0, 0 ,context.canvas.width,canvasContext.canvas.height );
Then JSONify the array and save that?

I have a JW Player implementation that won't work 'locally'

Users run my HTML files locally, straight from a CD.
I want to allow them to choose a bunch of videos and create a playlist on the fly.
This works very well if I run a web server but when I run the HTML itself it fails.
The player is created (using swfobject) and all my other code runs but playerReady never fires so I can never get the current play list to add to it.
Any ideas on how I can fix this or, more likely, work around it?

If the player is created, but you're not getting a playerReady, one of two things could be happening.
There's another playerReady on the page that's catching your playerReady. Make sure that there's just one playerReady on the page.
You haven't enabled JavaScript access for Flash. The code for that would look like this:
SWFObject:
var so = new SWFObject('player.swf','ply','470','320','9','#000000');
so.addParam('allowfullscreen','true');
so.addParam('allowscriptaccess','always');
so.addParam('wmode','opaque');
so.addVariable('file','video.flv');
so.write('mediaspace');
I should also note that there are some additional Flash security restrictions because you're accessing the player from disk. Namely, you can't access both a disk source and a network source (the Internet) simultaneously.
Best,
Zach
Developer, LongTail Video

Html5 Audio plays only once in my Javascript code

I have a dashboard web-app that I want to play an alert sound if its having problems connecting. The site's ajax code will poll for data and throttle down its refresh rate if it can't connect. Once the server comes back up, the site will continue working.
In the mean time I would like a sound to play each time it can't connect (so I know to check the server). Here is that code. This code works.
var error_audio = new Audio("audio/"+settings.refresh.error_audio);
error_audio.load();
//this gets called when there is a connection error.
function onConnectionError() {
error_audio.play();
}
However the 2nd time through the function the audio doesn't play. Digging around in Chrome's debugger the 'played' attribute in the audio element gets set to true. Setting it to false has no results. Any ideas?

I encountered this just today, after more searching I found that you must set the source property on the audio element again to get it to restart. Don't worry, no network activity occurs, and the operation is heavily optimized.
var error_audio = new Audio("audio/"+settings.refresh.error_audio);
error_audio.load();
//this gets called when there is a connection error.
function onConnectionError() {
error_audio.src = "audio/"+settings.refresh.error_audio;
error_audio.play();
}
This behavior is expressed in chrome 21. FF doesn't seem to mind setting the src twice either!

Try setting error_audio.currentTime to 0 before playing it. Maybe it doesn't automatically go back to the beginning

You need to implement the Content-Range response headers, since Chrome requests the file in multiple parts via the Range HTTP header.
See here: HTML5 <audio> Safari live broadcast vs not
Once that has been implemented, both the play() function and setting the currentTime property should work.

Q: I’VE GOT AN AUDIOBUFFERSOURCENODE, THAT I JUST PLAYED BACK WITH NOTEON(), AND I WANT TO PLAY IT AGAIN, BUT NOTEON() DOESN’T DO ANYTHING! HELP!
A: Once a source node has finished playing back, it can’t play back more. To play back the underlying buffer again, you should create a new AudioBufferSourceNode and call noteOn().
Though re-creating the source node may feel inefficient, source nodes are heavily optimized for this pattern. Plus, if you keep a handle to the AudioBuffer, you don't need to make another request to the asset to play the same sound again. If you find yourself needing to repeat this pattern, encapsulate playback with a simple helper function like playSound(buffer).
Q: WHEN PLAYING BACK A SOUND, WHY DO YOU NEED TO MAKE A NEW SOURCE NODE EVERY TIME?
A: The idea of this architecture is to decouple audio asset from playback state. Taking a record player analogy, buffers are analogous to records and sources to play-heads. Because many applications involve multiple versions of the same buffer playing simultaneously, this pattern is essential.
source:
http://updates.html5rocks.com/2012/01/Web-Audio-FAQ

You need to pause the audio just before its end and change the current playing time to zero, then play it.
Javascript/Jquery to control HTML5 audio elements - check this link - explains How to handle/control the HTML5 audio elements?. It may help you!

Chrome/Safari have fixed this issue in newer versions of the browser and the above code now works as expected. I am not sure the precise version it was fixed in.