Watching video using VNC

Jonathan Morton chromi "at" cyberspace.org
Thu, 21 Mar 2002 17:43:42 +0000


>Is this simply because that the video in application is a
>hardware solution, or do other graphical systems bypass VNC?

It's mostly restricted to video.  However, some early 3D cards 
(specifically the 3dfx Voodoo and Voodoo2) attached inline with the 
existing video adapter, and would also show this effect.  Such cards 
are largely obsolete now, mainly because of their age.

>What about
>somebody playing a high-framerate FPS shooter on the machine
>downstairs

Provided it's a full 2D/3D card, like most modern cards, it should 
show.  The same caveat with regard to performance applies, however, 
and you will probably see a framerate drop due to VNC's interference. 
You may also need to switch on full-screen polling, since VNC does 
not catch the "frame flip" events from the 3D engine.  Additionally, 
most games switch screen resolution to play, which will cause WinVNC 
to drop the connection, and you will need to reconnect the client 
during the game.

Approximately speaking, 3D rendering is done in a "back buffer", 
which is then flipped to the front buffer for display.  At all times, 
VNC is able to see the front buffer, whether it's used for 2D or 3D 
at the time.

>Or what about somebody playing a .MOV or .MPG file using a media
>player...would VNC pick that up?

Yes, in most cases, since the decoding is largely done in software 
and pasted to the main graphics framebuffer.  DVD playback on some 
hardware might not be captured, either because hardware MPEG decoding 
is in use, or because the software player is using a hardware 
acceleration on the graphics card, which in turn is bypassing the 
framebuffer.  ATI's "Rage Theatre" chip (featured on some Rage128 and 
most Radeon cards) might be an example here, but I can't confirm the 
behaviour because I don't have a DVD drive in that machine.

>I am just trying to better understand how VNC recreates the monitor input, and
>see how many unusual applications I can apply it to!!

It's mostly about how the video hardware creates it in the first place.

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from:     Jonathan "Chromatix" Morton
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