Hi, as usual, late reply, but hopefully it still helps.. <div class="gmail_quote">On Mon, Oct 18, 2010 at 2:40 PM, Greg Wunder <<a href="mailto:gwunder@eoir.com" target="_blank">gwunder@eoir.com</a>> wrote: <blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"> <div> Tracing the pipeline debug messages (noted below) showed that during the first fixate_caps() call, the input/output video sizes have been fixated already. Before that in the transform_caps() calls, the video sizes range [1, 32767], until the output video size is fixated into the input video size 320x240 & then fixate_caps() is called. I couldn't know the input video size, before the output video size has been set by the pipeline application. Using GstBaseTransform, the two functions called before setcap() are: 1) trans_class->transform_caps = GST_DEBUG_FUNCPTR (gst_mosaick_transform_caps); 2) trans_class->fixate_caps = GST_DEBUG_FUNCPTR (gst_mosaick_fixate_caps); </div></blockquote>If I understand well, here you need a caps renegotiation once the proper output size is known by the transformation element. More info here: <a href="http://www.gstreamer.net/data/doc/gstreamer/head/pwg/html/section-nego-upstream.html" target="_blank">http://www.gstreamer.net/data/doc/gstreamer/head/pwg/html/section-nego-upstream.html</a> This doc appears also to be quite handy: <a href="http://cgit.freedesktop.org/gstreamer/gstreamer/tree/docs/pwg/advanced-negotiation.xml">http://cgit.freedesktop.org/gstreamer/gstreamer/tree/docs/pwg/advanced-negotiation.xml</a> But I'd suggest, if you cloned the gstreamer core, to build the corresponding manual and read it instead of this xml file. Regards </div>