[Sugar-devel] GSoC Proposal: Multimedia Broadcasting

[Benjamin M. Schwartz]

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Eben Eliason wrote:
> On Fri, Apr 3, 2009 at 12:02 AM, Geza Kovacs <gkovacs at mit.edu> wrote:
>> Thanks for the responses. While I did consider the usefulness of
>> VNC-type remote desktop control interaction, which "Multi-point remote
>> desktop" seems to be
...
> Right. I'm actually on board with this point. I think VNC-style remote
> multi-pointer collaboration could be cool, but I, like you, also think
> there's plenty of benefit to be gained simply from the ability to
> "watch" someone else: either a single activity, or their full screen.

This is becoming very confusing.  Two points:

1.  Chris's Multi-pointer VNC is a very special, cutting-edge system.
Multiple pointers are not present in standard VNC.  Geza is right that our
toolkits and apps are not ready for MPX anyway.

2.  Standard VNC, by default has all mice controlling a single cursor, but
it can also be configured with behavior desired here.  For example, you
can launch "x11vnc -viewonly -shared", which allows many clients to
connect, but not provide any input.

Geza proposes to provide an audio stream, and a video stream that is
either from the videocamera (presumably as Theora video) or the contents
of the screen.

I think this is a really awesome proposal that would be hugely beneficial
to Sugar.  I see a few major technical difficulties to consider.

1.  Screen feeds and video feeds need different transports.  Our hardware
is not going to be capable of using Theora (or any other video codec) to
transmit the whole screen at acceptable quality, but it's also not going
to be capable of transmitting full motion video in VNC.  Therefore, we
need to use Theora for video and VNC for the screen capture.  This creates
a bit of a complex situation.  Perhaps VNC could be added to farsight as a
codec?

2. Telepathy does not currently support multi-point conferences.
Collabora is working on it, but from what I hear it's not likely to be
ready by June.  Thus, you will not be able to work entirely through
telepathy-farsight.  Farsight itself does support multi-point conferences
(I think...), but I am not sure that it has any optimization for the LAN
case, where all transmissions are essentially broadcast.  Transmitting
individual unicast streams to 30 laptops over a wireless network would be
an absolute disaster... but I assume that VNC requires the ordering and
delivery guarantees of TCP, so if you broadcast it clients will die as
soon they miss a packet.

3.  (distant third).  By default, VNC does not transmit the cursor as an
image.  Instead, it allows the client to show the local cursor.  This
makes sense, since because hardware acceleration means the cursor is often
not even in the framebuffer.  You will have to make the cursor visible
somehow, in order to act as a kind of "laser pointer".

IMHO, the proposal would be much stronger if it included solutions to
these problems.

- --Ben
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