Hope this is kosher, I'm not sure if a new plugin counts as a "PATCH" or not. 
The soon-to-be-attached .tar.gz file contains the .h and .c for the plugin and a
README, which I've pasted below.  Hope it's okay to attach binary files...

From the README:

So the purpose of this plugin/element is to allow processing of a partial media
stream.

The start and end points can be set using properties (start-offset and
end-offset).  Currently only time format is supported, so start-offset and
end-offset are expressed in nanoseconds.  If unspecified, the defaults will play
the entire stream.

When a buffer arrives, the clip element checks if that buffer's timestamp is
less than the start-offset.  If so, clip sends a seek event upstream (to
start-offset), and the buffer is disposed instead of pushed.  Otherwise, clip
checks if the buffer's timestamp is greater than or equal to the end-offset.  If
so, clip sends a seek event upstream (to the stream's total duration), and the
buffer is disposed instead of pushed.  If the buffer's timestamp is between
start-offset (inclusive) and end-offset (exclusive), then the buffer is pushed
downstream.

clip will not work if the upstream element does not support seeking.

Note that if start-offset is the same as end-offset, then exactly one frame will
be sent downstream by clip.

EXAMPLE USAGE:

gst-launch-0.8 filesrc location=x 
! spider 
! clip start-offset=y end-offset=y
! pngenc
! filesink location=z

The above is a command-line tool to take a snapshot of the frame at time offset
y in file x.  Without clip, there isn't a way to use gst-launch to take a
snapshot of anything other than the first frame; developers would have to write
tricky iterate loops to perform this common operation.

Another scenario is that of a video non-linear editor, in which start and end
points are selected by the end user and a string of clipped streams are played
back or exported.