How to convert a byte stream not from the beginning into raw video frames?

[sonntex]

I use fanout device in Linux to send video to many consumers.

http://linuxgazette.net/122/smith.html

First pipeline grabs video from web camera and writes it to the fanout
device.

gst-launch-1.0 -qe v4l2src device=/dev/video0 do-timestamp=true !
video/x-raw,width=640,height=480,framerate=30/1 ! videoconvert !
video/x-raw,format=I420 ! fdsink > /dev/fanout

Second pipeline reads video from the fanout device and encodes it.

cat /dev/fanout | gst-launch-1.0 -qe fdsrc do-timestamp=true ! videoparse
format=i420 width=640 height=480 ! videoconvert ! jpegenc quality=50 !
multipartmux boundary=boundary ! fdsink > video.multipart

It works good if I start second pipeline before first pipeline. But I
should read from the fanout device at any arbitrary time. Does gstreamer
have parser, or muxer and demuxer for raw video that can do it? For
example, h264parse can parse h264 byte stream from any position of the
stream. Probably, are there any workarounds?
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