[AG-TECH] VIC problems at 25fps

[Gary Kong]

Yeah, we have experienced exactly the same thing as well under our linux 
nodes.... As you said lowering the frame rate eliminates the problem. I 
actually go even further and reduce the frame rate to 15fps and the max 
bandwidth to 500 kbps. The GUI is very responsive even with 4 cameras. These 
settings have been chosen from observations of ag sessions. The remote sites' 
fps and network bandwidth usage rarely goes above these values anyway. And 
even if they do, the perceivable video quality difference is negligable. By 
using lower video resource settings, more of the processor and network 
bandwidth can go toward the audio side, which I think is far more important 
for a good session!

Gary

On Friday 12 Mar 2004 10:54 am, Steven wrote:
> Hello I have noticed a problem with vic on our machines here in the UK. The
> problem is manifested in two ways.
>
> 1.	The GUI for the vic window on the video machine is unresponsive,
> i.e. it is difficult to access GUI buttons, etc and the window often
> doesn't redraw correctly.
> 2.	On the display machine video windows which have been expanded remove
> themselves periodically. You can also notice that there has been some
> re-ordering of the transmitted windows within the vic application.
>
> It is as if the transmission is stopped and re-started. There are no join
> or leave requests on the network during this time.
>
> With some experimentation I found that altering the frame rate that you are
> transmitting changes this behaviour quite dramatically. Changing the frame
> rate below 25fps results in a responsive GUI on the video machine and the
> windows the displayed video streams remain stable. Indeed moving the frame
> rate up to 30 fps produces a similar fix, though the GUI is slightly
> hesitant in responding. Note that with a PAL signal connected the actual
> transmitted frame rate cannot achieve greater than 25 fps.
>
> I also noted that if there is no signal connected then the displayed
> streams are not interrupted. I also noted that this has little to do with
> the data rates involved as, there is little difference from sending black
> and burst signals to sending an 'off-air' TV signal resulting in data rate
> of approximately 1.5Mbps.
>
>
>
> In have repeated this on 2 different AG rooms and both behave identically,
> though tests with the PIG on a windows XP machine using a web cam were not
> able to demonstrate this effect.
>
>
>
> A quick fix is to set the 4 transmissions to 24 fps, but I wonder if anyone
> else is suffering from the same problems or has any insights.
>
> This obviously will only affect those using PAL sources, though it may be
> interesting for someone with an NTSC or indeed SECAM source to comment when
> running at 25fps.
>
>
>
> Steven
>
>
>
> Steven Jack
>
> Videoconferencing Manager
>
> University of Glasgow
>
> Computing Service
>
> Glasgow G12 8QQ
>
> UK
>
> Tel +44(0)1413303828 Fax +44(0)1413303820
>
> Email: s.jack at compserv.gla.ac.uk