Wifi is not very reliable for time sensitive stuff, the playback software would need to have a greater buffer.
I have had loads of issues playing even 720p stuff over a 802.11g lan - and thats only with video peaking at about 5 megabits - well short of the 20 that I get when benchmarking the lan most times.
Nature of the beast, either try some n wireless gear, or pull a cable for the ultimate solution, otherwise find if you can increase the buffer in the playing software.