[whatwg] HTML5 based Eduvid Slidecasting Demo

Narendra Sisodiya narendra at narendrasisodiya.com
Sun May 22 08:16:02 PDT 2011

On Sun, May 22, 2011 at 7:19 PM, Odin <odin.omdal at gmail.com> wrote:

> On Sun, May 22, 2011 at 3:03 PM, Narendra Sisodiya
> <narendra at narendrasisodiya.com> wrote:
> > infact I too want to do same..
> Cool!
> > Basically you want to send slides (via websocket or comet) and sync with
> > video..
> Yes. My old system (early Errantia) did that, using comet.
> > Here is the mistake. Sending Slides in real time has no use. Please
> > do not take me wrong. Basically in almost any conference or workshop,
> > presenter already has slides ready. So if something is ready then you can
> > directly push it to user. send video/audio in real time.
> You misunderstand :-) The slides are no problem at all, I upload them
> to the server, then when done it sends a Comet PUSH to the clients
> which tells them, a new slide resides at  """
> http://example.com/images/test-conference/14.jpg """. So that part is
> working swell.
> Also, I send the time when the slide appeared. However, the syncing to
> the video/audio is the impossible part, because there's no way for the
> browser to know where the video is in time/place **in a live
> setting**, you can very easily do this with archived video, it's just
> to read currentTime.
> We had a discussion about this, and that was why startOffsetTime made
> it into the spec:
> http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2010-May/thread.html#26342
> As you see, there are lots of buffering of video. And such, different
> people will be different places in the real time video.
> So I'm watching "live" and that's only one minute "off", whilst a
> friend is watching via wireless internet and is a full 10 minutes off
> because of his buffering etc, etc.
> In order to sync slides to the video/audio in such places (when people
> connect 10 minutes into the video and get a new currentTime = 0 at
> that time), you need a static reference point, but as of now; all time
> is still relative. Getting startOffsetTime will get us a static time
> to know when we're going to show the new slides (which will also have
> a  datetime  field for syncing).
Yes, I got your point.. I am sorry, I misunderstood your email. Also I was
not aware of problems in Live Video...

> > So , No need to send slides in real time.. Send all slides at once.. and
> > then keep on sending the configurations
> > I will also try to work on this...
> Well, for some conferences this won't work, and I already have code to
> do that live, so I don't need to send slides afterwards. Anyway, both
> ways work. But you need to know where people are in the video in order
> to sync to the slides; and that's where startOffsetTime come in.
> Alternatively you might try to control the buffers/caches, but that's
> not always possible. I've tried before, and can't really get it thight
> enough, there's too many variables, and Icecast might not be able to
> tweak itself to make a really good low latency low buffering live
> sending.
> --
> Beste helsing,
> Odin Hørthe Omdal <odin.omdal at gmail.com>
> http://velmont.no

│    Narendra Sisodiya
│    http://narendrasisodiya.com

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