gst-auto-launch is an improved version of gst-launch that accepts commands.

Usage: ./gst-auto-launch <pipeline description> <list of commands>
Where each command is of the form <seconds>:<name>

Supported commands are:
  pause:
    Change pipeline state to PAUSED
  seek:
    Seek to the specified time
  null:
    Change pipeline state to NULL
  stop:
    Change pipeline state to READY
  eos:
    Send eos to the source elements
  set:
    Set properties of an object
  quit:
    Quit the event loop
  ready:
    Change pipeline state to READY
  play:
    Change pipeline state to PLAYING
  navigation:
    Send the specified navigation event name to an element in the given coords

Example:
gst-auto-launch videotestsrc ! autovideosink 0:pause 1:play +5:eos
gst-auto-launch videotestsrc ! clockoverlay name=clock ! autovideosink 0:play 2:set:clock:valignment:bottom 5:eos