[PD] PS3 eye, Pix_video, low latency

IOhannes m zmoelnig zmoelnig at iem.at
Thu Oct 14 10:45:16 CEST 2010

On 2010-10-14 10:09, Jean-Marie Adrien wrote:
> Hi chris
> Im glad you jumped in. Concerning the topic would the following theory
> make sense ?
> it seems that video capture and video tracking do not adress the same
> purposes :
> - video capture allows 10 frames of latency to ensure that frame
> transfer is correct to the machine for later uses (post production,
> montage). This is the major usage now of video, because of DV camescopes
> and so on.
> - whereas video tracking requires 1 frame of latency maximum, to produce

which of course is not true at all.
it's like saying that audio capture for use with real time processing
requires a latency of 1 sample.

> real time responses. This is a emergent need, that seems to be covered
> by other softwares.

1 frame can be quite long, whereas 10 frames can be way shorter.

> Im trying to crawl to the second point.
> For instance, in pidip, it seems that there is a IE1394 object that
> processes DV type signals with a long latency, like pix_video does in
> GEM, and there is another object pdp_DC1394, that would be quicker, and
> could thus interface DC uncompressed industrial cameras without sticking
> them into the DVlike process, on Linux at least.
> Does this make sense ?

in Gem you don't have different objects for different grabbing APIs.
e.g. you would use [pix_video] for grabbing from your dv1394 consumer
camera, from your analog capture card and from IDC.

> Any DC pix_video object in GEM on MAC with 1 frame of latency ?
> DC1394 available on MAC or only on LINUX ?

on OSX, Gem uses QuickTime for about everything concerned with image
acquisition (thus all the problems with OSX10.6).
so on OSX this means: if QuickTime provides support for IIDC, then you
get IIDC in Gem; if QuickTime does not support GiG-E, then you don't
have GiG-E in Gem

on linux there is no grand unified image acquisition API, so there are a
number of different backends for the various APIs (thus: Gem has
explicit support for GiG-E and IIDC cameras on linux; it only has
implicit support (if at all) for those cameras on OSX)

and finally: the old rule-of-thumb was, that you get the best latency
with analog grabber cards you put into your PCI/express slot.


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