Hernan,
Pretty much all systems we have tested route cameras (and encoders) through a server in one way or another before the stream gets to the client. I haven't dug deep enough to determine if the server actually processes the video before sending it to the client or just routes it. It doesn't seem to matter based on our tests. As far as I can tell, with the possible exception of Pelco Endura (Avigilon is another matter due to their encoder "buffering" six frames), latencies are pretty much the same on all of the best systems +/- one frame (33ms). That appears to be the limit of our latency testing resolution. We did discover that multiple samples of a latency test yielded results within that range (33ms), so we concluded that testing was only accurate to that level. We chose to use the lowest latency from multiple samples of each encoder.
Since we're testing NVR/VMS systems, we aren't aiming to get the lowest latency possible, just the lowest latency a system can provide, with the caveat that there are many other factors we are testing for. High latency is enough to disqualify any given system but that also depends on our options. For instance, we tested Axis Q7406/Q7900, Bosch VIP X1600 XF, Sony SNT-EX154/SNT-EP154, TKH Siqura S-68 E and Verint S1808e encoders with the Genetec system to get an idea which encoders give the best picture quality, lowest latency and lowest bitrate for a given picture quality. We eliminated the Sony, TKH and Verint encoders for one reason or another. We are now testing a Geutebruck system with both the Axis and Bosch encoders. Although the Axis encoder has slightly lower latency than the Bosch in comparitive testing, we have not measured latency yet - that is scheduled for the next day or two.
Our observations have told us that each encoder has pluses and minuses. The Axis encoder has very slightly lower latency and slightly better resolution (due to its D1 capability vs. Bosch's 4CIF), while the Bosch has a slightly lower amount of noise. The Axis also tends to require lower bitrates than the Bosch - Axis' bitrate "settles down" under low/no motion conditions while Bosch, even in VBR, tends to run at, or even slightly above, any bitrate caps, even with no motion. The Axis also gets the nod during high motion (PTZ fast pan, for instance). Bosch's picture gets more macroblocking and other motion artifacting and takes longer for the picture to "settle down" after motion ceases.
Determining which encoder to specify will be difficult - we'll have to weigh many factors, including cost, rack space, redundancy, warranty and support and other capabilities to make the decision. That said, comparative testing on the IndigoVision system (IndigoVision's MPEG4 and h.264 encoders vs. the Axis and Bosch encoders), led us to conclude there is no point to specifying third party encoders if we choose IndigoVision. Their h.264 encoders provided comparable, or even superior, results to the others and were priced in the same ballpark when you factor license fees, etc. into the equation. Their MPEG4 encoders fell somewhat short in many regards.