In some scenarios it may be necessary to make adjustments to a windows computers filters (codecs).
Below is the most common tweak we make after installing the Combined Community Codec pack
If you haven't already installed the CCCP you can follow the instructions in this link
Download the attached Windows 7 Filter Tweaker
Launch on the affected PC
Click "preferred decoders"
On the left hand side of the screen under "32-bit decoders" change H.264 from "Microsoft" to "LAV Video".