It looks like the wiretap server is not properly validating input: due to a bug, my code would occasionally try to set the number of frames of a newly created clip to 0. That causes the wiretap daemon to crash with the message:
ifffsWiretapServer: /vobs/develop/src/libMedia/vmedia/videoMedia.C:113: VideoFrame VideoMedia::operator[](int) const: Assertion `frameIdx >= 0 && frameIdx < getNbFrames()' failed.
/usr/discreet/sw/sw_wiretapd: line 38: 31567 Aborted $server_prog $*