Gstreamer Missing plugins

Question

I am trying to run certain pipelines on the Command prompt for playing a video and I am often getting these errors/messages/warnings :

WARNING: erroneous pipeline: no element "qtdemux"
WARNING: erroneous pipeline: no element "playbin2"
WARNING: erroneous pipeline: no element "decodebin2"
ERROR: pipeline could not be constructed: no element "playbin".

Following are the pipelines :

gst-launch filesrc location=path to the mp4 file ! playbin2 ! queue ! ffmpegcolorspace ! autovideosink 

or

gst-launch -v filesrc location=path to the mp4 file ! qtdemux name=demuxer ! { queue ! decodebin ! sdlvideosink } { demuxer. ! queue ! decodebin ! alsasink }

or

gst-launch -v playbin uri=path to the mp4 file

or

gst-launch -v playbin2 uri=path to the mp4 file

Questions

1. I wanted to know, if I am I missing the plugins to execute this.
2. How do I know which plugin is responsible for which or found where?
3. What is the benefit of implementing the pipeline via c code.Are the missing plugins still required.
4. Is it good to install the missing plugins form the Synaptic manager or form the Gstreamer site(base,good,bad,ugly)

5. When we do gst-inspect we get output like this:

   postproc:  postproc_hdeblock: LibPostProc hdeblock filter
   libvisual:  libvisual_oinksie: libvisual oinksie plugin plugin v.0.1
   flump3dec:  flump3dec: Fluendo MP3 Decoder (liboil build)
   vorbis:  vorbistag: VorbisTag
   vorbis:  vorbisparse: VorbisParse
   vorbis:  vorbisdec: Vorbis audio decoder
   vorbis:  vorbisenc: Vorbis audio encoder
   coreindexers:  fileindex: A index that stores entries in file
   coreindexers:  memindex: A index that stores entries in memory
   amrnb:  amrnbenc: AMR-NB audio encoder
   amrnb:  amrnbdec: AMR-NB audio decoder
   audioresample:  audioresample: Audio resampler
   flv:  flvmux: FLV muxer
   flv:  flvdemux: FLV Demuxer
   

What does the x : y ( x and y mean ) ?

Answer 1

Answers,

It looks like gstreamer at your ends was not installed correctly. playbin2, decodebin2 are basic and part of the base plugins

1 Yes you may be missing some plugins

2 Use gst-inspect command to check if it is available

3 From C code you can manage states, register callback, learn more Yes missing plugins are still required

4 I guess gstreamer site would be better

5 Not sure about this one, would help if you arrange the result in a proper way