hi,

both cheese and ekiga does not work with my syneus (174f:5931) webcam while 
luvcview works fine.

linux is v2.6.29-rc8-124-g5bee17f, libv4l is 0.5.9 on debian sid.

This is what cheese -v says:

Cheese 2.24.3
Probing devices with HAL...
Found device 174f:5931, getting capabilities...
Detected v4l2 device: USB2.0 UVC PC Camera
Driver: uvcvideo, version: 256
Capabilities: 0x04000001

Probing supported video formats...
Device: USB2.0 UVC PC Camera (/dev/video0)
video/x-raw-yuv 1280 x 1024 num_framerates 1
7/1 video/x-raw-yuv 1280 x 960 num_framerates 1
7/1 video/x-raw-yuv 1280 x 800 num_framerates 1
7/1 video/x-raw-yuv 1024 x 768 num_framerates 1
7/1 video/x-raw-yuv 800 x 600 num_framerates 1
7/1 video/x-raw-yuv 640 x 480 num_framerates 1
20/1 video/x-raw-yuv 352 x 288 num_framerates 1
24/1 video/x-raw-yuv 320 x 240 num_framerates 1
24/1 video/x-raw-yuv 176 x 144 num_framerates 1
24/1 video/x-raw-yuv 160 x 120 num_framerates 1
24/1 video/x-raw-yuv 1280 x 1024 num_framerates 1
[snip]

v4l2src name=video_source device=/dev/video0 ! capsfilter
name=capsfilter
caps=video/x-raw-rgb,width=800,height=600,framerate=7/1;video/x-raw-yuv,width=800,height=600,framerate=7/1
! identity
libv4l2: error setting pixformat: Device or resource busy
libv4l2: error requesting 4 buffers: Device or resource busy

I've already asked on uvc devel and Laurent comes to this conclusion after 
looking at the driver logs you'll find attached:

That's definitely the problem. After calling VIDIOC_STREAMOFF to stop
streaming, cheese doesn't close the device and opens another instance. This 
is likely a bug in cheese or libv4l2.

thanks.
riccardo