[streaming] Re: Venus 2004 : which architecture ?

[Francois Meyer]

On Thu, 22 Jan 2004, Benjamin PRACHT wrote:

> Hello, here are 1 or 2 ideas about your project :
>
> - The archtecture you are panning makes  sense  to
>   me. However, be aware that you'll need  a  quite
>   recent computer tu plug the webcam in  :  you'll
>   need to make real time encoding, which  requires
>   some  cpu  power  (p4  1.5  GHz  for  real  time
>   fullscreen MPEG4 encoding).

Is there any alternative encoding option that  would
realize a compromise between quality and CPU needs ?

In fact the transmitted image will be rather  steady
and will have a good response  to  compression  (the
reason why I'd like to stream it live is because  of
the air turbulence that will really  render  like  a
real telescope view ; though, steady, the image will
be alive).

The webcam full res capability is limited to 640x480
but I would like to stick at  least  at  320x240  if
possible.


> - which way will you use to stream on the internet
>   on the servers ?

Well, that is part of my question :) I  am  open  to
any suggestion on that topic. I  am  really  new  to
streaming and I barely have a small idea of what  is
possible to setup in such a case.

> Using vlc as a udp multicast -> http  proxy  would
> make sense, in my opinion. However, be aware that,
> as far as I know, no high load test, with lots  of
> http connections have been made on vlc.  In  fact,
> we would be pleased to get some feedback  on  that
> point

I will be trying to make some test runs as soon as I
have the basic bricks to build the system.  June  is
still far, but a lot of  work  has  to  be  done  to
qualify the stuff. Your help will be REALLY valuable.

>
> - vlc is unable to command a dv  camera  directly.
>   You will need to use an external program to  set
>   the camera, then have  vlc  read  the  resulting
>   video directly on a device / fifo, and transcode
>   the result in a streamable format.  This  should
>   be possible,  but  hasn't  really  been  tested,
>   AFAIK.

Ok. The DV item is a 'cherry on the cake' option, in
case we  quickly  solve  the  main  problem.  Anyway
controlling the camcorder is not really an  issue  :
the  camcorder  is  not  intended  to  be   remotely
operated ; grabbing the stream is the only  thing  I
intend to do with vlc.

I summarize the key points of the  problem  at  this
stage and my  degree  of  understanding  of  how  to
address them :

1. grab the webcam stream ;

        Ok, no problem (I think).

2. encode the stream :

        need your help on  the  format  to  be  used
        keeping in mind the constraints I developped
        in the beginning of my message (320x240, 5
        im/s, rather steadyi, high  contrast  image,
           and no audio needed at least in  a  first
           stage...)

3. multicast the result to the server(s) :

        I think I could go through this one,  though
        your help is still welcome.

4. provide access to the stream from the internet :

        select some clients that we want to be  able
        to read the stuff, or stick to vlc ?

        according to he  above  result,  select  the
        method to provide access to the stream.

5. evaluate   the   per    user    bandwidth,    CPU
   requirements, number of servers needed ;

        this will be done once point  4  is  solved,
        getting feedback from the  first  test  that
        I'll try to setup asap.

Ok that is enough for now.

I will start to address point 1  and  3  adopting  a
generic solution for point 2 just to setup the first
tests.

I am carefully listening to your thoughts about
all that.

Thank you again and in advance.

-- Francois Meyer   (Please, no html, no MSWord attachment) 
Tel : (+33) 3 81 66 69 27   Fax : 3 81 66 69 44 
Observatoire de Besancon - BP1615 - 25010 Besancon cedex - FRANCE
**** Université de Franche-Comté ****** CNRS UMR 6091 *****


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