[vlc-devel] Re: [RFC] E-learning with VideoLAN

Henri Fallon henri at via.ecp.fr
Thu Jan 9 01:01:41 CET 2003

On Tue, Jan 07, 2003, Alexis de Lattre wrote:
> I have put our ideas in a RFC document available here :
> [PDF format] : http://www.via.ecp.fr/~alexis/rapport-dla.pdf

A few thoughts about this :

 my understanding of the problem is that we must transmit and display
other than video and audio from a server to our clients. 

 This data could be in any format, which is a separate point.

 You will also want your "slide data" to be synchronized, and maybe
 the user to be able to go back, on the slides (maybe not I guess).

For the transport of the data, you could either rely on an external
protocol (ie. http) or put the data in the MPEG TS stream.

For the synchronization, an easy solution is to send "triggers" in the
MPEG stream to tell the client that it should be displaying this
slide (or this file, or whatever).

About the format, I'm not sure you should choose a format and stick
to it. You could have a generic frame within the vlc with various 
capacities (exploiting vlc's modules handling). This frame could for 
instance contain a Batik viewer, or a gecko, or a realplayer applet.

Actually if you choose to have the transport in the MPEG stream, you
just end with another decoder, with its own synchro, just as audio
or subtitles.

The difficulty with not restricting the slides to one format is finding
a way for the "synchro" to happen : in most SVG presentation you trigger
an scripted event changing the display attribute of a section, while in
html you would rather go to another file. Your slide component should
support generic events, (that you can feed to the component such as the
SVG or html engine) and a file on the server should have the timing and
the event to send.

So I guess now you need to define the format of the synchro and
a way to embed the slides in the stream (especially how to cope
with lost packets) or decide to use a "get" approach.

henri, I never mkae typos 
there's only one - http://henrisson.net/ - accept no substitutes
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