Virtually all ports build from source at one time or another.
I've added the missing curl and pkgconfig dependencies in r94091; thank you for reporting that.
As for the mkvextract malloc error message, I don't know how to reproduce that. When I run "mkvextract" with no arguments, it correctly prints the usage message. If you have a reproduction recipe, you can post it here, however the responsibility for fixing the problem ultimately lies with the developers of mkvtoolnix, so you should report the problem to them.
