As a few others have reported, the later versions of melt seem to have some issues. I couldn't get any rendering to complete with version 0.7.8 of melt either from the standard debian repositories or from debian-multimedia.org.
What I did was go to snapshot.debian.org and get the last of the 0.7.6 version from there. This version worked.
Four packages need to be installed with dpkg -i
These should then be put on hold in aptitude so they do not get updated accidentally. (Press = on the package).
The strange thing is that from what I read the issues was supposed to be fixed in the 0.7.8 release, but it seems that they are still there.