[PD] webcam problem in Gem with Ubuntu Intrepid/Pd-extended 0.41.4-rc3

abonnements-olivier abonnements-olivier at heinry.fr
Mon Jun 1 18:51:56 CEST 2009

Thank you Iohannes for pointing out the low-level side-effects and
glitches/potentiality eg. hard-disk instead of a webcam. Once again,  an
experimental system (jaunty with libv4l-dev) against a stable one
(hardy) is a hard choice. 

Havent grilled any cat yet, but must be tasty!

On lun, 2009-06-01 at 17:10 +0200, IOhannes m zmölnig wrote:
> abonnements-olivier wrote:
> > 
> > and for the next session
> > echo "export LD_PRELOAD=/usr/local/lib/libv4l1/v4l1compat.so" >> ~/.bashrc
> > 
> actually i would not recommend this.
> LD_PRELOAD seriously interferes with how application linking works (and 
> is therefore usually discouraged); the sole purpose of it is to allow 
> library calls be intercepted and provided by a different backend, 
> something useful when doing debugging or swapping a backend for a single 
> application (like chromium does with openGL apps; or libv4l-compat in 
> our case).
> otoh, the only thing that libv4l compat can actually intercept is calls 
> to ioctl(), which is deep on the kernel-side. overriding ioctl for each 
> and every application is probably really not what you want.
> apart from slowing everything down (as it wraps a system call!), you 
> might turn otu seeing your harddisk as a webcam. probably nice pictures, 
> but bad data.
> (surely libv4l-devs are trying to do everything to not do any harm when 
> wrapping system calls; but they will most likely have bugs in their code 
> as everybody)
> thus the way to go, is to compile an application with native libv4l support.
> anyhow, i just wanted to point out, that people here are lately 
> suggesting a log of brute force "solutions", which might work fine but 
> nevertheless i think it would be proper to warn anybody that they might 
> just grill their cat.
> fgmasdr
> IOhannes

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