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

IOhannes m zmölnig zmoelnig at iem.at
Mon Jun 1 17:10:40 CEST 2009

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.


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