makefile - ffdec_h264 (video decoder) GstElement not found, libgstffmpeg.so already linked, works fine from command line gcc but not from cmake -

some of lines myapp.c file

... gstelement* video_decoder; video_decoder = gst_element_factory_make ("ffdec_h264", "video_decoder_one"); assert(video_decoder); ... 

when compiled using command line gcc, compiles/ runs fine,

gcc -o app myapp.c `pkg-config --cflags --libs gstreamer-0.10 gstreamer-app-0.10 `

now wanted use cmake(like else!) , hence added fancy lines, after trying various approaches given on stack overflow... pkg_check_modules(), execute_process() etc. of them resulted in errors like

error : assertion 'video_decoder' failed

question 1 -
issue here, have included/ linked same way gcc compile command ?

so, tried check ffdec_h264 , normal gcc compile command have picked

$ gst-inspect-0.10 ffdec_h264

resulted in

plugin details:

      name:           ffmpeg            description:    ffmpeg codecs , formats (local snapshot)         filename:       /usr/lib/gstreamer-0.10/libgstffmpeg.so            version:        0.10.12         license:        lgpl         source module:  gst-ffmpeg          binary package: ffmpeg           origin url:     http://ffmpeg.org/ 

the element present in /usr/lib/gstreamer-0.10/libgstffmpeg.so

i tried confirm, hence ran pkg-config --cflags --libs gstreamer-0.10 gstreamer-app-0.10 on command line , got

-pthread -i/usr/local/include/gstreamer-0.10 -i/usr/include/glib-2.0 -i/usr/lib/i386-linux-gnu/glib-2.0/include -i/usr/include/libxml2 -pthread -l/usr/local/lib -lgstapp-0.10 -lgstbase-0.10 -lgstreamer-0.10 -lgobject-2.0 -lgmodule-2.0 -lgthread-2.0 -lrt -lxml2 -lglib-2.0

question 2 - (less priority) don't see gstffmpeg shared-object being linked pk-config above, still compilation using gcc works , code runs fine. how ?

however, same compilation/run using cmake seems not working me.

other normal stuffs, have below line in cmakelists.txt

find_library(gst_ffmpeg_libraries names gstffmpeg paths /usr/lib/gstreamer-0.10/) 

and linked it, refer find_library()

question 3-
have linked exact .so name ffdec_h264 present, why give same error of element not found. can tell me debug option dig more or might wrong here?