[GEM-dev] Re: [PD] multiple_window feature of Gem?

[Jeremy Cooperstock]

Greetings all,
  IIRC, the TOT project is using DVTS or a derivative thereof, in which 
case, the software is already multicast capable (although perhaps not in 
the base release).

  Our UltraVideoconferencing system is expected to gain multicast 
capability (hopefully for both IPv4 and IPv6) later this year and this 
would serve (at least) for DV, analog, or SDI video distribution.  Since 
our needs entail processing of the video as per the requirements of each 
receiver, and with minimal latency, DV would not be a suitable candidate 
for this purpose, given the encoding and decoding costs, so we're 
considering instead raw transmission of a bounding box region of 
segmented (i.e. background-removed) video.  In the typical case, this 
payload would fit comfortably on a 100Mbps network, although 
segmentation problems or scene discontinuities that lead to full frame 
transmission would require either compression or gigabit infrastructure.

- Jeremy

B. Bogart wrote:

> Thanks for the link, I'll take a look when I have more time.
>
> Ok so its Chromium itself that passes the texture data through the
> cluster. Indeed video would be more difficult, but with a 1Gbps
> multicast lan one should easily be able to distribute a DV stream to all
> machines... in theory! Are there multicast DV streamers???
>
> The streaming part fits very well into TOT.
>
> I've CCed Franz Hildgen and Simon Piette who are looking after the DV
> point-2-point application teleCHACHA.
>
> Franz and Simon, we're talking about pd/Gem working in a cluster
> context, where the GL context is forwarded to a number of machines that
> each processes and projects one part of the image. This is very closely
> related to the lighTWIST and pixelTANGO integration problem.
>
> Would it be possible to multicast a DV stream to all the cluster
> machines, so that each could use the stream in its portion of the final
> image?
>
> Mike Wozniewski from McGill is looking at using chromium with pd/Gem for
> a cave application.
>
> B>
>
> Mike Wozniewski wrote:
>
>> Hey.
>>
>>> I did not see a link to any in depth documentation from chromium.
>>
>>
>>
>> Check http://chromium.sourceforge.net/doc/index.html. Very 
>> comprehensive.
>>
>>> I'm not a c++ programmer so I'm not sure
>>> what it would involve to build these functions into GL wappers for Gem.
>>> I'm not sure how the functions latch onto an existing context, and how
>>> the whole thing works architecturally (what parts run on what machines,
>>> master slave connections etc..
>>
>>
>>
>> Well, from the docs, it seems that we don't have to do anything at all
>> to Gem. This is because Chromium disguises itself as the OpenGL library
>> - ie, when a GL instruction is made, Chromium intercepts and the regular
>> system OpenGL library sits idle.
>>
>>> I just wonder about performance, considering the speed of the AGP bus
>>> for texture transfers vs ethernet transport between the source and
>>> destination for the texture! especially if your talking about moving
>>> video...
>>
>>
>>
>> So according to http://brighton.ncsa.uiuc.edu/%7Eprajlich/wall/ppb.html,
>> when distributing video, the movie has to first be played in "write
>> mode", where all textures are cached onto the disks across the cluster.
>> Then subsequent playback is done in "read mode", where it's just read
>> from local disk on each machine. I see problems with this in that all
>> videos have to exist on disk first (no streaming from live cameras), the
>> first playback is going to be SLOW, and if you have many many video
>> clips this could be extremely annoying.
>>
>>> (are you guys even using video in your cave application?)
>>
>>
>>
>> Not yet. But we will eventually want to put video avatars of remote
>> participants into the world (ouch - this is not going to work with the
>> above mentioned strategy).
>>
>> -Mike
>>
>>

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