[jitsi-users] webcam recognized but no video in Debian 7.2 (Jitsi latest nightly build)

Dear All,
I setup Debian 7.2 on my Thinkpad Z61m with external webcam (Logitech
C170) to use it with Jitsi (for internal webcam the driver is outdated
and camera is not recognized by Jitsi nb 4900)

The external webcam is instantly recognized in Debian and displays nice
video on Cheese, Skype and testing using "gstreamer-properties".

However in Jitsi using video both preview and videocalls dont work, only
black window, although under tools/options/video/devices the webcam is
selected ("Webcam C170 (dev/video1)" and the webcam LED is on.

I checked online and in the forum for background infos and paste below
the terminal output of lsusb and v4l2 -ctl --all (however the v4l2 -ctl
- --all command only lists the parameters of the internal webcam, but not
the external Logitech ?? )

Any suggestions and help is welcomed!
kind regards, MS

[this command also did not make video working:
LD_PRELOAD=/usr/lib/i386-linux-gnu/libv4l/v4l2convert.so jitsi ]

user@debian:~$ lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 002: ID 046d:082b Logitech, Inc.
Bus 001 Device 003: ID 0424:2502 Standard Microsystems Corp.
Bus 001 Device 005: ID 0a5c:2110 Broadcom Corp. Bluetooth Controller
Bus 001 Device 006: ID 0c45:627b Microdia PC Camera (SN9C201 + OV7660)
Bus 004 Device 002: ID 0483:2016 SGS Thomson Microelectronics
Fingerprint Reader

user@debian:~$ v4l2-ctl --all
Driver Info (not using libv4l2):
        Driver name : sn9c20x
        Card type : USB20 Camera
        Bus info : usb-0000:00:1d.7-5.2
        Driver version: 3.2.51
        Capabilities : 0x05000001
                Video Capture
                Read/Write
                Streaming
Format Video Capture:
        Width/Height : 640/480
        Pixel Format : 'S920'
        Field : None
        Bytes per Line: 640
        Size Image : 460800
        Colorspace : SRGB
        Custom Info : 00000002
Video input : 0 (sn9c20x: ok)
Streaming Parameters Video Capture:
        Frames per second: invalid (0/0)
        Read buffers : 2
user@debian:~$