I'm not sure I understand what you mean by the "right framerate".
qtdemux (and decodebin if used alone) pull the framerate from the
file. If its playing back at a weird framerate, you might want to try
re-encoding the file. Does a tool like mplayer report  a sensible and
stable framerate?

If the file is playing back at some steady framerate but not the one
you want, gstreamer *does* have some tools for dealing with that.

If you have a file encoded at a particular framerate, n, and you want
to view it at some other framerate, n', you can use the videorate
tool.

To, for example, playback a video at quarter framerate:

export GSCAM_CONFIG="filesrc location=file.mov ! qtdemux name=demux
demux.video_00 ! decodebin ! ffmpegcolorspace ! videorate !
video/x-raw-rgb,framerate=1/4 ! identity name=ros ! fakesink"

framerate=2/1 would playback at double framerate, and so on.

One thing to note is that videorate only changes the framerate and not
the duration. There might be a way to do that with gstreamer, but I
don't know of one off the top of my head. In a case where you want to
change a file's duration it's probably easier just to re-encode the
file.

A ros-centric equivalent to the videorate tool is Willow's throttle
node: http://www.ros.org/wiki/topic_tools/throttle

Sorry if I'm a bit murky on what you're wanting. Does any of that seem helpful?

_Trevor