converting jpeg to h263p and streaming over RTP

[Aleksander Dutkowski]

hi!

I have a webcam, which produces jpeg images, and I want to convert
this stream into h263p and then put it into RTP stream.
I am playing with various configurations, using of course [1] scripts,
but when adding rtph263ppay, v4l2 is crashing:

So this one works:
gst-launch-0.10 -v -e v4l2src device=/dev/video0 \
! 'image/jpeg,width=640,height=480,framerate=30/1'  \
! jpegdec  \
! "video/x-raw-yuv, format=(fourcc)I420, width=(int)640,
height=(int)480, framerate=(fraction)30/1" \
! ffmpegcolorspace \
! ffenc_h263p \
! "video/x-h263, width=(int)640, height=(int)480,
framerate=(fraction)30/1, variant=(string)itu,
h263version=(string)h263p, annex-f=(boolean)true,
annex-j=(boolean)true, annex-i=(boolean)true, annex-t=(boolean)true" \
! fakesink

but this one...
gst-launch-0.10 -v -e v4l2src device=/dev/video0 \
! 'image/jpeg,width=640,height=480,framerate=30/1'  \
! jpegdec  \
! "video/x-raw-yuv, format=(fourcc)I420, width=(int)640,
height=(int)480, framerate=(fraction)30/1" \
! ffmpegcolorspace \
! ffenc_h263p \
! "video/x-h263, width=(int)640, height=(int)480,
framerate=(fraction)30/1, variant=(string)itu,
h263version=(string)h263p, annex-f=(boolean)true,
annex-j=(boolean)true, annex-i=(boolean)true, annex-t=(boolean)true" \
! rtph263ppay \
! fakesink

... results in following error:
Setting pipeline to PAUSED ...
ERROR: Pipeline doesn't want to pause.
ERROR: from element /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: Could
not negotiate format
Additional debug info:
gstbasesrc.c(2830): gst_base_src_start ():
/GstPipeline:pipeline0/GstV4l2Src:v4l2src0:
Check your filtered caps, if any
Setting pipeline to NULL ...
Freeing pipeline ...

I'm confused, why v4l2src is crashing, as I add element to the end of
the pipe. I checked src and sink of all elements, and it looks good.