[gst-devel] v4lsrc confusion

[Bertrik Sikken]

Thomas Vander Stichele wrote:
>>I was trying to set up a pipeline to view the video stream coming
>>from my webcam (sonix based), using a V4L(1) driver. The pipeline
>>I'm trying to use is
>>v4lsrc -> ffmpegcolorspace -> ximagesink
>>
>>Setting this up in gst-editor gives me a dialog telling me that
>>it could not set a parameter, but after dismissing this I can
>>see the webcam video stream in a window.
>>If I try this using gst-launch
>>gst-launch v4lsrc ! ffmpegcolorspace ! ximagesink
>>it gives me a similar message (from the v4lsrc module).
> 
> 
> When reporting problems, could you please paste the actual error ? It's
> more useful than a vague report on what it is, esp. when you're asking
> what the error means :)

Here's the output I get:

[root at vleermuis gst-plugins-0.8.6]# gst-launch -v v4lsrc ! 
ffmpegcolorspace ! ximagesink
RUNNING pipeline ...
ERROR: from element /pipeline0/v4lsrc0: Could not get/set settings 
from/on resource.
Additional debug info:
gstv4lsrc.c(663): gst_v4lsrc_src_link: /pipeline0/v4lsrc0:
Could not set framerate of 1.000000 fps
/pipeline0/v4lsrc0.src: caps = video/x-raw-rgb, bpp=(int)24, 
depth=(int)24, endianness=(int)4321, red_mask=(int)255, 
green_mask=(int)65280, blue_mask=(int)16711680, width=(int)352, 
height=(int)288, framerate=(double)1, pixel-aspect-ratio=(fraction)1/1
/pipeline0/ffmpegcolorspace0.sink: caps = video/x-raw-rgb, bpp=(int)24, 
depth=(int)24, endianness=(int)4321, red_mask=(int)255, 
green_mask=(int)65280, blue_mask=(int)16711680, width=(int)352, 
height=(int)288, framerate=(double)1, pixel-aspect-ratio=(fraction)1/1
ERROR: from element /pipeline0/v4lsrc0: Could not get/set settings 
from/on resource.
Additional debug info:
gstv4lsrc.c(663): gst_v4lsrc_src_link: /pipeline0/v4lsrc0:
Could not set framerate of 30.000000 fps
/pipeline0/v4lsrc0.src: caps = video/x-raw-rgb, bpp=(int)24, 
depth=(int)24, endianness=(int)4321, red_mask=(int)255, 
green_mask=(int)65280, blue_mask=(int)16711680, width=(int)352, 
height=(int)288, framerate=(double)30, pixel-aspect-ratio=(fraction)1/1
/pipeline0/ffmpegcolorspace0.sink: caps = video/x-raw-rgb, bpp=(int)24, 
depth=(int)24, endianness=(int)4321, red_mask=(int)255, 
green_mask=(int)65280, blue_mask=(int)16711680, width=(int)352, 
height=(int)288, framerate=(double)30, pixel-aspect-ratio=(fraction)1/1
/pipeline0/ffmpegcolorspace0.src: caps = video/x-raw-rgb, 
width=(int)352, height=(int)288, framerate=(double)30, bpp=(int)32, 
depth=(int)24, red_mask=(int)65280, green_mask=(int)16711680, 
blue_mask=(int)-16777216, endianness=(int)4321, 
pixel-aspect-ratio=(fraction)1/1
/pipeline0/ximagesink0.sink: caps = video/x-raw-rgb, width=(int)352, 
height=(int)288, framerate=(double)30, bpp=(int)32, depth=(int)24, 
red_mask=(int)65280, green_mask=(int)16711680, blue_mask=(int)-16777216, 
endianness=(int)4321, pixel-aspect-ratio=(fraction)1/1
/pipeline0/v4lsrc0.src: active = TRUE
/pipeline0/ffmpegcolorspace0.sink: active = TRUE
/pipeline0/ffmpegcolorspace0.src: active = TRUE
/pipeline0/ximagesink0.sink: active = TRUE
Execution ended after 1 iterations (sum 76284000 ns, average 76284000 
ns, min 76284000 ns, max 76284000 ns).
/pipeline0/v4lsrc0.src: active = FALSE
/pipeline0/ffmpegcolorspace0.sink: active = FALSE
/pipeline0/ffmpegcolorspace0.src: active = FALSE
/pipeline0/ximagesink0.sink: active = FALSE
/pipeline0/v4lsrc0.src: caps = NULL
/pipeline0/ffmpegcolorspace0.sink: caps = NULL
/pipeline0/ffmpegcolorspace0.src: caps = NULL
/pipeline0/ximagesink0.sink: caps = NULL
[root at vleermuis gst-plugins-0.8.6]#

BTW, running 'gst-launch v4lsrc ! fakesink` seems to run fine.

>>I thought v4l does not have any property to set the framerate.
> 
> v4l by itself does not.  Two types of webcams do, however, using the
> same mechanism, which is why I put it in v4lsrc for now.  (These two
> kinds are the ones handled by the pwc.ko module, and the ones handled by
> the quickcam.ko module).  I might move it out at a later point because
> there is more camera-specific stuff handled by these modules which would
> make no sense to put into v4l directly.
> 
>>I tried various combinations of setting properties sync-mode
>>and autoprobe-fps, but without success.
> 
> What type of webcam do you have ?

It's a 'sweex 100k', which consists of a sn9c101 camera controller
and a PAS106B CMOS image sensor. I'm running it with a V4L1 driver
from http://sourceforge.net/projects/sonix

>>Another, more general thing I wonder about:
>>Is it possible to have controls for v4l?
>>For example, being able to control brightness, contrast,
>>whiteness, color and hue.
> 
> Yes, this is exported through a GstInterface.  Read all about it in
> Ronald's excellent Plugin Writers Guide, available on your favourite
> GStreamer website.

Ok, thanks, I'll check that out.

Kind regards,
Bertrik


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