Re: [GnomeMeeting-list] H261PixelEncoder : H.261 bad geometry: 320x240

[Damien Sandras <damien sandras it-optics com>]

Hi,

Le mer 07/01/2004 à 10:04, Van Duc Uy a écrit :
> Hi all,
> I use gnomemeeting-0.98.5 on Mandrake linux 9.2.
> camera is Logitech Quickcam Pro 4000. 
> 
> it's because gnomemeeting always display the picture with a
> BIG "Gray border" (as i know GM_QCIF_HEIGHT/WIDTH). 
> 
> so i want to choose another mode GM_SIF_WIDTH/HEIGHT that
> displayed at 320/240 pixels. 
> After i modified the gnomemeeting code, and rebuilt it, 
> the video can display very well without border anymore. ..
> 
> But, when i try to make a connection to another host (Netmeeting 3.0),
> at the console i saw the message :
> 
> H261PixelEncoder : H.261 bad geometry: 320x240
> Segmentation fault
> 
> and then gnomemeeting crashed.
> 
> Can anyone explain for me about the problem ?

You modified things without understanding. If it was possible to do it
so easily, it would already be a feature ;)

> why H.261 can not encoder with 320/240 pixel ?

Actually, the H.323 standard specified that at least H.261 QCIF must be
supported by endpoints. So, if you are sending SIF or QSIF, there is no
guarantee that the remote endpoint will be able to decode it. The
OpenH323 H.261 encoder, which is the vic encoder, only supports QCIF and
CIF.

> If i don't want to see the "Gray border", how can i do ?
> 

There are 2 possibilities :
- Buy a camera that supports exactly QCIF and CIF
- Modify vconvert.cxx in pwlib so that it supports image scaling.
Currently, pwlib will ask to the driver to capture in QCIF, if the
driver supports it, it will work. If the driver doesn't support QCIF,
pwlib will try the next size and surround it with borders. So it will
try QSIF, for example, and surround it with borders so that it becomes
QCIF. You could extend the methods so that the QSIF is scaled in QCIF
instead of surrounded by borders. However, that won't work with the
logitech quickcam, because when you request QCIF, the driver will itself
send QSIF surrounded by borders, without the intervention of the
library, there are thus 2 things to do :
	* extend pwlib colour converters so that they support scaling 	instead
of cropping/borders
	* fix the driver so that it fails when QCIF is asked, instead of
	adding itself the borders

Good luck!

-- 
 _      Damien Sandras
(o-     
//\     It-Optics s.a.
v_/_    GnomeMeeting: http://www.gnomemeeting.org/
        FOSDEM 2004:  http://www.fosdem.org
        H.323 phone:  callto:ils.seconix.com/dsandras seconix com