There are two essential (and free) utilities that will solve a host of video incompatibility problems with Apple’s QuickTime utility. They are free to download, and easy to install. CreativeTech recommends installing these on most Mac creative workstations.
Perian — Billed as the Swiss-Army knife for QuickTime. This open source plug-in for QuickTime includes a wide number of video codec files that enables your Mac to play most cross-platform video formats.
Filp4Mac WMV — Provides support for Microsoft’s Windows Media files (WMV) — one of the few video formats Perian doesn’t support. The free version allows you to play most WMV files. You can pay to unlock additional options for exporting and converting WMV files into other formats.