I cant seem to find a thread related to this so I have started my own.
8.4.3 had major problems crashing when exporting quicktimes - Ive just upgraded to 8.4.4 and get the same probelms - quicktime exports fine, then when trying to do fast export it locks up and gives fatal error - even when I have unticked the fast export box (makes no difference).
Just re-installed 8.4.2 and all works perfectly.
Mac Pro (late 2013)
Yosemite 10.10.5
3.5GHz 6-core Intel Xeon E5
16 GB 1866 MHz DDR3 ECC
AMD FirePro D500 3072 MB
Flash SSD 251GB
Have installed latest BM desktop video 10.5.2 with Ultrastudio Thunderbolt connection