The question is that, we have to write a pipeline which should take video as input, encode with h264 , and save it with .264 extension, and again we have to decode it, and play it
for encoding we used this:
gst-launch videotestsrc ! ffmpegcolorspace ! x264enc ! filesink location=/home/vutp/ru.264( no error at encoding)
for decoding we used this:
gst-launch filesrc location=/home/vutp/ru.264 ! ffdec_h264 ! ffmpegcolorspace ! xvimagesink(error at decoding)

Error what am getting is:
Setting pipeline to PAUSED ...
Pipeline is PREROLLING ...
ERROR: from element /GstPipeline:pipeline0/ffdec_h264:ffdec_h2640: Internal GStreamer error: negotiation problem.  Please file a bug at http://bugzilla.gnome.org/enter_bug.cgi?product=GStreamer.
Additional debug info:
gstffmpegdec.c(2729): gst_ffmpegdec_chain (): /GstPipeline:pipeline0/ffdec_h264:ffdec_h2640:
ffdec_h264: input format was not set before data start
ERROR: pipeline doesn't want to preroll.
Setting pipeline to NULL ...
Freeing pipeline ...