Trying to send video (from bttv interface) over network.
gst-launch v4l2src device=/dev/video1 ! xvimagesink works OK.

Using (anonymous) CVS

Sending with:
gst-launch v4l2src device=/dev/video1 \
  ! video/x-raw-yuv, width=352, height=288 \
  ! ffmpegcolorspace \
  ! ffenc_h263 \
  ! video/x-h263 \
  ! rtph263ppay pt=96 \
  ! udpsink host=10.28.1.3 port=8800 sync=false
Setting pipeline to PAUSED ...
Pipeline is live and does not need PREROLL ...
Setting pipeline to PLAYING ...
New clock: GstSystemClock

Receiving with:
gst-launch udpsrc port=8800 \
  ! application/x-rtp, clockrate=90000, payload=96 \
  ! rtph263pdepay queue-delay=0 \
  ! ffdec_h263 \
  ! xvimagesink
Setting pipeline to PAUSED ...
Pipeline is live and does not need PREROLL ...
Setting pipeline to PLAYING ...
New clock: GstSystemClock
0:00:00.200136382 32527 0x839e288 ERROR               ffmpeg gstffmpegdec.c:1852:gst_ffmpegdec_frame:<ffdec_h2630> no codec context
ERROR: from element /pipeline0/ffdec_h2630: Internal GStreamer error: negotiation problem.  Please file a bug at http://bugzilla.gnome.org/enter_bug.cgi?product=GStreamer.
Additional debug info:
gstffmpegdec.c(2243): gst_ffmpegdec_chain (): /pipeline0/ffdec_h2630:
ffdec_h263: input format was not set before data start
Execution ended after 3021593 ns.
Setting pipeline to PAUSED ...
Setting pipeline to READY ...
Setting pipeline to NULL ...
FREEING pipeline ...