This indicates an attack attempt to exploit a Heap Buffer Overflow vulnerability in Apple QuickTime.
The vulnerability is due to insufficient validation when parsing a MP4 file with a malformed atom. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted QuickTime mp4 file.
Apple Quicktime 7.7.6 in Windows 7 and Windows Vista
Apple Quicktime 7.7.6 in OS X Mountain Lion v10.8.5, OS X Mavericks v10.9.5, OS X Yosemite v10.10 to v10.10.3
System Compromise: Remote attackers can gain control of vulnerable systems.